U.S. patent number 3,873,741 [Application Number 05/329,578] was granted by the patent office on 1975-03-25 for air regulation in the pyrolysis of wood to produce liquid smoke for the treatment of food products.
This patent grant is currently assigned to The Griffith Laboratories, Inc.. Invention is credited to Irving Melcer, Louis Sair.
United States Patent |
3,873,741 |
Melcer , et al. |
March 25, 1975 |
Air regulation in the pyrolysis of wood to produce liquid smoke for
the treatment of food products
Abstract
A method for producing a liquid smoke product to be used in
imparting a wood smoke stained appearance and a wood smoke taste to
comestibles. The method involves the controlled carbonization
combustion of wood in the presence of a regulated critical
concentration of air, the air being introduced in an amount from
about 3 to about 50 cubic feet of air for each pound of wood
burned.
Inventors: |
Melcer; Irving (Park Forest,
IL), Sair; Louis (Evergreen Park, IL) |
Assignee: |
The Griffith Laboratories, Inc.
(Chicago, IL)
|
Family
ID: |
23286063 |
Appl.
No.: |
05/329,578 |
Filed: |
February 5, 1973 |
Current U.S.
Class: |
426/650; 201/29;
426/332; 426/431; 95/188; 426/314; 426/474 |
Current CPC
Class: |
A23B
4/0526 (20130101); A23L 27/27 (20160801) |
Current International
Class: |
A23L
1/232 (20060101); A23B 4/052 (20060101); A23L
1/226 (20060101); A23B 4/044 (20060101); A23l
001/27 () |
Field of
Search: |
;201/27,34,28-30
;426/312,314,315,332 ;202/182,183,184,210 ;55/68,73 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yudkoff; Norman
Assistant Examiner: Ribando; Curtis P.
Attorney, Agent or Firm: Kegan, Kegan & Berkman
Claims
What is claimed is:
1. In the method of controlled carbonizing combustion of wood to
produce a liquid smoke product for use in imparting a
wood-smoke-stained appearance and a wood-smoke taste to comestibles
treated with said product, which method includes the steps of:
heating wood in a chamber in the presence of an oxygen-controlled
atmosphere to effect thermal decomposition of the wood and to
generate smoke,
contacting said smoke with water to provide an aqueous extract
thereof and to condense and to recover from said smoke a volatile
distillate contained therein, and
separating from said condensed volatile distillate water-insoluble
components entrained therein;
the improvement comprising providing, during heating of the wood in
the chamber, air in a concentration of from about 3 to about 50
cubic feet of air for each pound of wood carbonized;
thereby to produce in high yield a clear, readily dilutable aqueous
liquid smoke product free from carcinogenic compounds,
said liquid smoke product being further characterized by enhanced
smoke taste, smoke aroma, and food coloring capacity.
2. The method of claim 1 wherein the separation from said condensed
volatile distillate of water insoluble components entrained therein
is carried out by the steps of:
retaining the water extract of said smoke in a storage vessel in a
physically undisturbed state for a finite time period to permit
substantially complete precipitation of said water insoluble
components from said water extract to provide two distinct layers
in said vessel, said layers comprising a clear supernatant
overlying a water insoluble tar-like residue,
removing said clear supernatant from contact with said tar-like
residue, and
retaining said clear supernatant as said liquid smoke product.
3. The method of claim 1 and further comprising the steps of
recirculating said aqueous extract of said smoke in a zone of
contact with said smoke to increase in said extract the
concentration of said volatile distillate contained in said smoke,
thereby more effectively and efficiently to extract said smoke and
to provide a liquid smoke product exhibiting enhanced smoke flavor
and smoke-color-imparting capabilities when applied to comestibles
treated therewith.
4. The method as set forth in claim 3 wherein the rate of
recirculation of the water extract is in the range of from about 10
to about 80 liters of extract per pound of wood carbonized;
whereby the yield of liquid smoke product is increased, flavor and
color factors are improved, and carcinogens are eliminated.
5. The method of claim 1 wherein, during heating of said wood in
said chamber, air is provided in a concentration of from about 5 to
about 30 cubic feet of air for each pound of wood burned.
6. The method of claim 1 wherein, during heating of said wood in
said chamber, air is provided in a concentration of from about 7 to
about 20 cubic feet of air for each pound of wood burned.
7. A liquid smoke product produced in accordance with the method of
claim 1 and characterized by
improved color imparting capabilities, enhanced taste-imparting
characteristics, freedom from carcinogenic material, and
a high degree of dilutability.
Description
BACKGROUND OF THE INVENTION
The treatment of foods with wood smoke is one of the oldest means
used in food preservation. In contemporary commercial practice the
treatment with wood smoke is employed primarily for the
characteristic color and flavor which are developed.
The prior art describes many different ways of exposing the food
products to smoke or smoke media, and a widely adopted practice has
been to expose the food products directly to a smoke atmosphere
produced upon combustion of wood or sawdust. The food products,
thus exposed to the smoke, would gradually take on the usual and
desired smoky flavor and character, and the smoked appearance.
Smoke generators, or wood burning apparatus which has been used in
the past to produce the desired smoke atmosphere, have certain
inherent disadvantages the recognition of which has been a stimulus
for extensive research for more convenient and more reliable and
reproducible techniques. The smoke produced or obtained from wood
fires cannot be effectively controlled as to concentration or
density. Such a process cannot be relied upon to produce a product
of consistent quality or character due not only to the variability
in the woods used but also to the difficulty in controlling the
buring process itself and, therefore, the nature of the smoke
product produced.
Wood smoke is recognized to be a most complex chemical system
including both vapor and particulate components. Except through the
use of the most sophisticated equipment and regulatory apparatus,
the smoke obtained from wood fires cannot be controlled either as
to quality or quantity. As a result, there has been a recognized
lack of uniformity of the smoked food product produced from plant
to plant even when utilizing the "same" equipment in a direct
smoking system.
Until the advent of more modern technology, the most common methods
used in the direct smoking of food products have been the burning
of damp hard wood sawdust in a batch operation, the heating of dry
sawdust, or the burning of wood in a friction process. In any of
these techniques the food product to be treated was suspended in a
smoke house filled with the smoke or was subjected to the
electrostatic precipitation of smoke particles onto the surface of
the food product. In all of the techniques, the taste and the color
imparted to the food is a function of the specific wood used and
the technique employed, and differ from batch to batch.
In addition to the shortcomings of the techniques described above,
the smoke house used in direct smoking has major shortcomings which
have proven to be inefficient and to be undesirable for modern
production goals. Original cost investments are objectionably high
and frequent replacement of the mechanical components of the smoke
generating equipment is required. There are continuous problems in
maintaining the duct work adequately clean, and fires are not
infrequent.
From the standpoint of ecology, the smoke houses have been
notorious for creating air pollution problems. Deposits on the
walls and duct work of the physical installation as well as in the
fans and other equipment used are highly objectionable and
necessitate time-consuming and costly cleanup in order to ensure
adequate compliance with promulgated sanitation and safety
standards.
The employment of conventional direct-smoking techniques has failed
to solve the problems of guaranteeing uniformity in the smoky
flavor or in the degree of color imparted to the food product, from
batch to batch. The quality of treated comestibles has been most
difficult to control, because the properties of the smoke itself
have not been controllable. Additionally, the technique has been
overly demanding in the time required to achieve the desired taste
and color levels.
In the direct smoking methods particulate as well as vapor
components of the smoke deposit on the food products being
processed. Since it has been established that the particulate phase
of the smoke often includes carcinogenic compounds, the deposit of
such particulates on food products should be avoided.
Because of the many shortcomings and objectionable features
inherent in the direct smoking methods, other techniques have been
sought, and extensive research has been carried out in this area of
food treatment. Among the alternate proposals has been the use of a
product described as "liquid smoke," a substance which may be
defined, generally, to include liquid reagents capable of imparting
smoky hue or coloration and/or smoky flavor to a comestible exposed
to the liquid or to its vapor phase. The use of liquid smoke has
important advantages over the predecessor direct smoking
techniques. For example, this preparation is much more convenient
in use and has been considerably more effective in achieving
reproducible smoke taste and smoke coloration in the products
treated, provided adequate controls are utilized and appropriate
precautions taken. Whereas the usual direct smoking technique
ordinarily involves a batch process, it has been found feasible and
convenient to use continuous processes when smoking with the aid of
liquid smoke. The continuous processes have effected substantial
cost savings, particularly since less elaborate equipment is needed
than that called for in the prior art smoke house. Through the
installation of relatively simple and reliable controls, the need
for skilled personnel is also eliminated.
From a pharmacological viewpoint, it has been possible to eliminate
from the liquid smoke the carcinogenic hydrocarbons and other
compounds which are physiologically undesirable and which are
normal constituents of wood smoke.
Several techniques have been found useful in adapting liquid smoke
as a medium by which smoky flavor and a smoked appearance may be
imparted to meet products and other comestibles. One procedure is
to dip the food product directly into the liquid smoke. An
alternative procedure is to treat the food products with a
vaporized phase or with fine spray of the liquid smoke. In still
other techniques the liquid smoke has been subjected to a flash
evaportion step whereby the liquid product is nebulized or
vaporized to establish an atmosphere effective in the "smoking" of
the product contained in the treatment zone. Alternatively, a
controlled quantity of the liquid smoke may be incorporated
directly into the food product.
SUMMARY OF THE INVENTION
The present invention relates to an improved method and apparatus
for producing liquid smoke, and to the products produced thereby.
More particularly, the invention is directed to a process in which
wood or wood products and equivalent raw materials are subjected to
a controlled carbonizing combustion in the presence of a regulated
air supply and an aqueous extraction system, whereby there is
produced a liquid smoke having markedly improved flavor and
significantly enhanced capabilities for coloring the food products
treated therewith. Related important features of the improved
liquid smoke product of the invention are that the liquid is
readily dilutable, is produced in high yield, and is completely
free of carcinogenic materials.
It is an important practical and commercial feature of the
invention that the method is characterized by a high degree of
reproducibility so that the resulting liquid smoke products are
uniform in both their qualitative and their functional character,
and in their effectiveness in use.
It is an important discovery of the present invention that there
exists a critical relationship between the aeration level or the
amount of air used during the combustion of the wood to produce
liquid smoke, and those properties of the liquid smoke which are
significant from a commercial standpoint.
While some general studies have been made in the past to
investigate the nature of the chemical composition of wood smoke
(Pettet and Lane, A Study of the Chemical Composition of Wood
Smoke, J. Soc. Chem. Ind. 59, 114 (1940)), and while, generally,
there exist data indicating an interrelationship between the nature
of the chemical compounds contained in smoke preparations and the
conditions under which the wood is burned, none of these data have
shown the criticality of utilizing a specific, limited range of air
concentration during the combustion process.
It is a related important feature of the present invention that, in
addition to the effect of air in determining the precise chemical
compounds contained in the smoke product itself, it has been
established that the amount of air supplied during the combustion
process is a most decisive factor in establishing the "quality" of
smoke produced for use on food products.
Whereas data contained in the literature have reported an
interdependence between the chemicals contained in the smoke
combustion, these data provide little if any suggestion as to any
criticality in the relationship as it may affect the quality of
liquid smoke to be used in food processing. It is an important
feature of the present invention that there has been established a
critical airflow concentration which ensures optima in flavor, and
dilutability of the liquid smoke produced.
It is a related important feature of the invention that within the
discovered critical air concentrational range it is possible to
obtain a maximum yield of a high quality liquid smoke product.
Yet another important feature of the liquid smoke product produced
in accordance with the method of the invention is that the liquid
smoke is free of carcinogenic materials.
A related advantage of the method of the invention is that the
liquid smoke produced is carcinogen-free without any need either
for distillation or filtration, or cyclonic separation.
It is an important discovery of the present invention that the
quantity of air needed to produce an optimum liquid smoke product
is significantly less than the calculated air necessary to achieve
"total combustion" of the wood itself.
An unpredictable and surprising discovery of the invention is that
the amount of air to be used in producing an optimum liquid smoke
product is about one-sixth of the calculated air required to effect
complete combustion of the wood.
It has been established that in the pyrolysis of wood, increased
aeration produces increased masses of glowing charred wood,
promoting destructive distillation as well as establishing a highly
oxidizing atmosphere, the two effects opposing one another.
However, with increased air flow rates the contact time between the
smoke product and the hot pyrolysis zone is shortened. This latter
factor modifies the above-described effects.
It is an important feature of the invention that the process
produces a remarkably uniform commercial product which is reliably
duplicated from run to run and which has essentially constant food
flavoring and food coloring capacities.
In a preferred embodiment of the invention water circulated through
an extraction tower, and running countercurrent to the smoke
produced, is effective to extract the smoke to provide the liquid
smoke product of the invention.
It is a related feature of the invention that the water extract of
the smoke evolved during combustion may be recirculated through a
packed absorption tower further to concentrate the smoke elements
in the extract solution, thereby to facilitate the production of a
concentrate of any desired properties and strength.
DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram indicating the various functional
components utilized in the apparatus for carrying out the method of
the invention;
FIG. 2 is a perspective drawing illustrating, schematically,
smoke-generating apparatus suitable for use in practicing the
method of the invention; and
FIG. 3 is a graph illustrating the critical relationship between
degree of aeration and yield of liquid smoke product.
DEVELOPMENTAL WORK AND ANALYTICAL TECHNIQUES
The prior art includes publications which refer to the use of air
during the pyrolysis of wood. However, these references are
singularly devoid of quantitative disclosures and are inadequate to
provide sufficient information for those skilled in the art to
calculate the precise aeration level utilized. For example,
Hollenbeck U.S. Pat. No. 3,106,473 refers to the burning of wood
"with a limited amount of air," and compares that procedure with
the destructive distillation of wood carried out in the absence of
added air.
Fessman U.S. Pat. No. 3,634,108 describes a wood smoke-generating
process in which superheated steam is used in conjunction with air
enriched with oxygen or a mixture of oxygen and inert gas. In each
case the system is used directly in conjunction with the actual
food smoking operation. However, the data presented are
insufficient to permit calculation of any aeration levels achieved.
Fessman claims as a preferred concentration the use of a mixture of
oxygen and an inert gas in which the oxygen is in the range of from
about "0.5 to 5 parts by volume to 100 parts of steam by volume."
It may be deduced that the oxygen level is extremely low since the
ultimate product of pyrolysis is a "black carbon-like granulated
residue, which can be burned again in air."
ANALYTICAL PROCEDURES FOR PRODUCT EVALUATION
In the experimental work carried out which culminated in the
discovery constituting the method of the present invention, the
liquid smoke product was analyzed with respect to several
parameters including solids content, acidity, precipitable solids,
flavor, and color factor. In each case the procedure adopted was
the following:
1. Solids: an aliquot of the smoke solution was weighed on a
predried standardized circle of Wattman No. 40 paper, and then
dried for 2 hours in an oven at 105.degree. C., in a forced
draft.
2. Acidity: a 1.0 gram sample of the liquid smoke dissolved in 100
milliliters of water was titrated with standard NaOH solution to a
pH of 8.15, and calculated as acetic acid.
3. Precipitable Solids: four milliliters of water was added to a
2.0 gram sample of liquid smoke and mixed, centrifuged 10 minutes
at 2,400 rpm, and the supernatant discarded. The residue was washed
with two 5-milliliter aliquots of water, dried 2 hours at
105.degree.C. in a forced draft oven, and the weight of residue
calculated as percentage of the initial sample.
4. Flavor: a triangle testing procedure using a nine-man panel was
used. A sample of from 10 to 40 milligrams of liquid smoke was
diluted to 250 milliliters in a soup containing 1 per cent salt and
4 per cent wheat flour. The panel was then asked to identify the
odd sample on the basis of smoke flavor strength. In additional
test procedures frankfurters previously dipped in a liquid smoke
solution and processed in a smoke house were similarly
evaluated.
5. Color Factor: color evaluations were conducted on both bacon and
franks. In the bacon test 5 grams of the liquid smoke was sprayed
on a 2 .times. 2 .times. 4 inch piece of cured pork belly which had
been prewarmed by rotating for 8 minutes at a distance of 2 inches
below a 250-watt infrared lamp. The bacon was then cooked by
rotating an additional 15 minutes, after which it was chilled over
night and the fat surface evaluated for smoked appearance.
Frankfurters were dipped for 6 seconds in the liquid smoke,
processes in a smoke house, chilled, peeled and evaluated for
surface color.
The experimental investigation involved in development of the
subject invention was carried out using three different types of
smoke-generating equipment: laboratory and commercial retorts, a
meat packing house type of smoke generator, and a rotating
calciner. In the experimental work conducted, various types of
hardwood were used. These included maple board, maple and hickory
log sections, and maple and hickory sawdust. The equipment was
controlled to achieve flameless combustion in each instance so that
the ultimate solid product from the wood was charcoal rather than
ashes.
LIQUID SMOKE PRODUCED IN CHARCOAL RETORT
An externally heated retort, provided with openings for the
introduction of controlled quantities of air, was charged in each
run with 1,000 grams of dry maple clippings. One run was conducted
with no air added, and subsequent runs were carried out with
aeration levels at 0.07 cubic foot of air per pound of wood and at
0.16 cubic foot of air per pound of wood. The results are tabulated
below in Table 1.
Table 1 ______________________________________ Effect of Aeration
on Liquid Smoke Produced in a Laboratory Retort Run No. 1 Run No. 2
Run No. 6 ______________________________________ Aeration Level
0.07 0.16 0 (cu.ft./lb.) Carbonization Tem- 437-887 437-734 437-734
perature (.degree.F.) Liquid Smoke Analysis: % Solids 8.4 9.4 10.8
% Acidity 15.3 15.3 15.4 Color Factor on Slightly Darker Lighter
Bacon lighter than S-10 than S-10 than S-10
______________________________________
In order to provide a meaningful reference and a useful basis of
comparison between the liquid smoke product produced experimentally
and the commercially available liquid smoke products, the
experimentally produced products were compared with a commercial
product herein identified as S-10. This reference product is
advertised in the trade as having been produced in accordance with
the teachings of Hollenbeck U.S. Pat. No. 3,106,473. That process
involves the production of liquid smoke by burning wood in a
"limited" amount of air, the smoke being absorbed in a
recirculating countercurrent flow of water passing through a packed
absorption column. A similar process is described in Ash U.S. Pat.
No. 2,670,295. The Hollenbeck liquid smoke product is filtered
through cellulose pulp to remove carcinogenic materials, while the
liquid smoke product of Ash is distilled. Neither filtration nor
distillation constitutes a process step in producing the liquid
smoke product of the present invention.
A typical analysis of the commercial product identified as produced
in accordance with the Hollenbeck process is as follows: % Solids
8.7 % Acidity as acetic acid 9.9 % Precipitable solids 0.33
There are no data in the Hollenbeck patent indicating the aeration
level employed or the carbonization temperature.
In a commercial carbonizing run, corresponding generally to the
conditions set forth in Table 1, 40,000 pounds of wood (maple or
hickory) per retort load was processed using 258 cubic feet of air
for each 3,000 pounds of dry wood (0.086 cubic foot per pound), to
produce liquid smoke at a yield of 11.7 percent by weight
calculated on the basis of 7 percent solids in the liquid smoke
product. This yield is a significant improvement over a 6.9 percent
yield obtained in a process in which essentially no outside air was
supplied during the combustion cycle (the production of
pyroligneous acid). The increase in yield is clearly attributable
to the addition of the air.
The liquid smoke product from several retort runs was combined and
subjected to analysis, the results of which are set forth in Table
2.
Table 2 ______________________________________ Characteristics of
Smoke Product from Retort ______________________________________ %
Solids 10.6 % Acidity as acetic acid 18.8 % Precipitable solids 1.9
Flavor 2-3 times as "strong" as S-10, and somewhat harsh Color
factor on bacon equal to or slightly darker than S-10
______________________________________
As indicated above, compared to the reference standard S-10 the
liquid smoke product from the retort is, as a practical matter,
deficient in color since it was necessary to resort to a more
concentrated product in order to achieve a comparable color factor.
The product is strong in flavor but is inferior from the standpoint
of dilution characteristics since it exhibited a high concentration
of precipitable solids (tar). The smoke product, after being
allowed to settle several weeks, produced a supernatant which was
completely free of carcinogenic materials.
In summarizing the work carried out with the retort apparatus,
aeration levels up to about 0.16 cubic foot of air per pound of
wood are effective to provide an increased yield over that obtained
in the production of pyroligneous acid. However, the aeration level
achieved is inadequate to develop the other desirable properties of
a liquid smoke, that is, good flavor, good color factor, and good
durability. Since increased aeration using the retort was not
practical because of the hazard created by the presence of
explosive mixtures within a totally enclosed structure, further
experimental work was carried out using a different type of
apparatus, specifically, a packing house type of smoke
generator.
LIQUID SMOKE PRODUCED IN PACKING HOUSE TYPE OF SMOKE GENERATOR
In order to establish the effects of aeration levels higher than
those obtainable utilizing a sealed retort, a series of
investigations was carried out utilizing a packing house type of
smoke generator in which the carbonization of wood was conducted in
a continuous, relatively open system. The generator itself
constituted a 5 -foot long horizontal tube or duct which was
externally heated and contained a coaxial, variable drive screw
effective to carry and move sawdust at a rate of up to about 10
pounds per hour from a supply reservoir located at one end of the
tube to a charcoal outlet at the opposite end.
The smoke generated in this machine was drawn upwardly by means of
a fan to pass through an absorption column packed with 1.7 cubic
feet of 1-inch ceramic saddles, the smoke traveling countercurrent
to a downwardly flowing stream of water introduced at the top of
the column from a reservoir therebeneath. This technique and
apparatus are similar to those described in Ash U.S. Pat. No.
2,670,295. The vapor effluent from the column was vented through an
adjustable damper system which served to regulate the draft of a
fan assembly and, accordingly, the level of aeration occurring
during the pyrolysis of the wood.
In accordance with the preferred embodiment of the method of the
invention, the water was recycled to effect a concentration of the
desirable smoke components. The strength of the liquid smoke
preparation was also controlled by regulation of the rate and the
duration of the wood pyrolysis and by adding water to replace that
lost through evaporation.
The packing house smoke generator made feasible the use of aeration
levels as much as 1,000 to 10,000 times that possible with the
retort. While normally such levels would tend to produce open
combustion and complete ashing of the wood, by keeping the contact
time of the air and the wood, and the external heat applied at
minima, it was possible to obtain flameless pyrolysis with charcoal
as the end product. Yields of liquid smoke as a function of the
aeration level are tabulated in Table 3, for air used at the rate
of from about 160 to about 1,800 cubic feet per pound of wood. In
each experimental run carried out 10 to 15 pounds of sawdust were
used.
Table 3 ______________________________________ Effect of Aeration
Level on the Yield of Liquid Smoke Utilizing a Packing House Smoke
Generator Yield of Liquid Experiment No. Air Usage Smoke at 7%
Solids ______________________________________ (cu.ft./lb. Wood) (%
of Wood by Weight) 24-58 158 24 24-47 250 24 24-31 483 21 24-33 515
21 24-41 980 20 24-43 1820 18
______________________________________
The 18 to 24 percent yield of liquid smoke product, based on the
weight of the wood pyrolyzed, is about twice that obtained in the
sealed retort (11.7 percent yield). The data also show a decrease
in yield with increasing aeration. This decrease may be due to loss
of desirable smoke ingredients in the spent smoke discharged from
the apparatus. Accordingly, it is important that the aeration rate
not exceed the "capacity" of the equipment used.
The yield obtained from the smoke generator apparatus is also
affected by the rate of recirculation of liquid in the absorption
column. As indicated in Table 4, lower yields are achieved at
relatively low recirculation rates.
Table 4 ______________________________________ Effect of
Recirculation Rate on Yield of Liquid Smoke Using a Packing House-
Type Smoke Generator Wood Yield of Expt. Pyrolysis Aeration
Recirculation Liquid Smoke No. Rate Level Rate at 7% Solids
______________________________________ (lbs./hr.) (cu.ft./
(ml/min.) (% of Wood lb.) by Wt.) 24-38 4.2 510 380-500 11 24-31
4.1 483 1800 21 24-33 4.3 515 3000-5000 21
______________________________________
When the size of the absorption bed (packed column) is limited, the
rate at which the extracting water is recirculated has a
compensatory effect, but only up to a point beyond which there is
no further improvement. In an extension of the smoke generator
work, reported below, the size of the absorption column was
increased by a factor of about 10 (15.7 versus 1.7 cubic feet) and
the absorptive surface of the column by a much larger factor
through the use of 1/2 inch rather than 1-inch saddles. At the same
time, the carbonization rate was increased by only a factor of 5.
Under the conditions described, there were no apparent improvements
in the yield when the recirculation rate was increased from about
3,500 to about 52,000 milliliters per minute. The results indicate
that the absorptive surface of the column was more than adequate to
accommodate the pyrolysis rate employed. The larger scale runs
carried out with the smoke generator apparatus are summarized in
Table 5 below.
Table 5
__________________________________________________________________________
Production of Liquid Smoke Utilizing Packing House-Type Smoke
Generator Experiment 24-75 24-83 24-92
__________________________________________________________________________
Sawdust: Total Usage, lbs. 80 110 130 Rate, lbs./hr. 7.4 5.5 5.9
Temperatures (.degree.F.): Smoke, 4 inches above Bed 290-330
287-330 290-340 Smoke, 18 inches above Bed 254-275 260-280 250-285
Smoke, entering Column 178-222 168-214 160-215 Liquor, exiting
Column 101-113 81-101 87-108 Aeration, cu.ft./lb.: 167 222 211
Liquid Recirculation, ml/min.: 6000 6000 6000 Yields: Charcoal, %
of Sawdust 34 39 33 Liquid Smoke, % Sawdust 32 32 33 Liquid Smoke,
ml at 7% Solids 11,815 15,960 19,400
__________________________________________________________________________
The most significant practical effect apparent from the large-scale
runs is that the yield of the smoke product was significantly
higher, being about 33 percent as opposed to 20-24 percent for the
smaller scale runs. It is believed that this increased yield
reflects a more efficient absorption of the smoke components by
full strength liquid smoke as compared with water. It will be
appreciated that in the smaller scale experimental runs most of the
time of the run is utilized in building up the strength of the
starting absorption fluid (water), while in the longer duration
runs this period is relatively shorter and a larger fraction of the
extraction time utilizes a liquid extractant which already includes
a relatively significant fraction of the water soluble smoke
components.
The liquid smoke products of run 24-75 and of run 24-83 of Table 5
were combined, aged one week to permit the settling of suspended
tars, and then retained as liquid smoke product lot 24-89. A
similar settling procedure was carried out with the liquid smoke
product of Experiment 24-92 of Table 5, and the final supernatant
product identified as lot 24-97. Lots 24-89 and 24-97 were analyzed
to provide the data set forth in Table 6 below in which the
properties of the product are compared with the S-10 standard.
Table 6
__________________________________________________________________________
Analysis of Laboratory Prototypes of Drenching Liquid Smoke Lot
24-89 Lot 24-97 Reference S-10
__________________________________________________________________________
% Solids 8.0 7.0 8.7 % Titratable Acidity as Acetic Acid 7.2 8.3
9.9 % Precipitable Solids (1 + 2 dilution with water) 0.11 0.10
0.33 Flavor - Soup Test 67% 80% 100% Color Factor on Bacon Darker
Darker Standard than S-10 than S-10
__________________________________________________________________________
The several effects of high aeration readily apparent. Color factor
is built up to such a value that as little as 7 percent of solids
in the smoke product provides a coloring capacity which exceeds
that of the S-10 standard which has about 8.7 percent of solids.
Since a liquid smoke preparation having 7 percent solids is
completely suitable as a commercial product, the 7 percent solids
product is used as a basis for comparisons in calculating yields,
in the work reported herein.
Other effects of extremely high level aeration include the
following:
1. A reduction in flavor as compared with the reference S-10. This
is believed to be attributable to volatilization or oxidation and
removal of smoke components, particularly acid components and
phenols, such products being known to impart an acrid or medicinal
taste to liquid smoke. A tempering of the flavor of the final
product in the respect indicated is believed to be a desirable aim,
since the product thus produced may be conveniently used even when
only a mild smoky taste is desired.
2. A reduction in precipitatable solids. It is believed that this
is due to an elimination of "cracking" or solubilization of tars
which ordinarily occurs when little or no air is used. Again, this
feature is believed to be desirable in a commercial liquid smoke
product.
3. Freedom from carcinogenic hydrocarbons. A sample of the lot
24-89, after settling for one week and being decanted from the
insoluble tars, was found to be completely free of carcinogenic
hydrocarbons, e.g. benzpyrene. This important beneficial effect is
believed to be due to the insolubilizing effect of the air on tars,
which then permits ready removal of the tar-carried carcinogens as
a water insoluble fraction.
Upon comparing the data developed in the experimental work carried
out with the sealed retort with the data from the packing house
smoke generator, it may seem that each desirable property of the
liquid smoke product is enhanced by increasing the aeration level.
Such improvement would appear to hold true for yields as well as
for flavor and color. However, further investigative work, in an
aeration region or zone intermediate the very low aeration of the
retort and the exceedingly high aeration of the packing house smoke
generator, provided results which were not only unpredictable, but
which were completely unexpected. Specifically, an important
element of the subject invention is the discovery that there exists
a critical aeration level in which the liquid smoke product yield
is markedly superior to that achieved either at extremely low
aeration rates (below 3 cubic feet of air for each pound of wood
burned) or high aeration rates (above about 50 cubic feet of air
for each pound of wood burned). Moreover, it has been discovered
that the higher yields obtainable in this relatively narrow
intermediate aeration zone are achieved without sacrificing the
other desirable properties of the liquid smoked product.
Surprisingly, it has been discovered that by carrying out the
controlled combustion of the wood at an aeration rate within the
limit defined, one can achieve an optimum balance between all of
the desirable smoke properties on one hand and the yield on the
other.
LIQUID SMOKE GENERATION USING A COMMERCIAL CALCINER
A commercial calciner was used as the means of conducting a series
of runs to explore the effect of aeration rates intermediate those
obtainable through the use of the sealed retort and the packing
house smoke generator. A style "D" calciner manufactured by the
Bartlett-Snow Company proved to be eminently suited for this work.
Like the packing house smoke generator, the calciner included an
elongated tube (6 inches in diameter and 7 feet long) which was
heated externally to carbonize sawdust passing from a feeder at one
end of the tube to a charcoal discharge outlet at the other.
However, whereas the packing house smoke generator used a screw or
auger as the means for propelling the sawdust through the
combustion tube, in the commercial calciner the entire tube was
rotated. The rate of feed of the sawdust into the tube, coupled
with the specific inclination of the tube with respect to the
horizontal, regulated the rate at which the sawdust passed through
the calciner.
Drawn through the calciner by means of an exhaust fan, the flow
rate of the air was controlled by an adjustable damper positioned
ahead of the fan. An accurate record of the volume of air passing
through the tube was provided by means of a calibrated rotameter.
The air was metered as it entered the apparatus at the charcoal
discharge port. The air entering the apparatus passed over the
pyrolysis zone and carried with it the smoke generated in the
calciner, the smoke being drawn past the sawdust input end of the
apparatus and into the duct work connected to the absorption
column, all as indicated schematically in FIG. 2. In the particular
embodiment of the apparatus used, the absorption tower was 2 feet
in diameter and packed with 1/2 inch ceramic saddles to a height of
about 5 feet, representing a volume of 15.7 cubic foot of packing.
Countercurrent circulation and recirculation of water through the
packed column effected an absorption of the smoke, in a manner
similar to that described with reference to the packing house smoke
generator. The spent gases exited from the column past a damper and
a fan and were, thereafter, exhausted to atmosphere. Absence of
significant exhaust smoke indicated substantially complete smoke
absorption in the column.
The principal parameter studied utilizing the commercial calciner
was aeration, which was explored in the range of from about 8 to
about 45 cubic foot of air per pound of wood processed. Other
operating variables were maintained essentially constant from run
to run, and were as follows: Wood used Hickory, maple (8-15%
moisture) Wood feed rate 23 - 36 lbs/hr. Wood processed per run 105
- 300 lbs. Calciner rotation rate 9 rpm (Maximum) Calciner pitch 1
inch per linear foot Dwell time of wood in calciner 6 - 7 minutes
Pyrolysis zone temperature 345 - 600.degree. F. Temperature of
smoke leaving calciner 160 - 238.degree. F. Temperature of smoke
entering absorp- tion column 141 - 194.degree. F. Temperature of
recirculating liquid smoke 78 - 127.degree. F. Recirculation rate
3,000 - 53,000 ml/min.
For each run the temperature was at the lowest level at the start
and climbed to the highest point as equilibrium was reached,
generally within 1 hour. Similarly, the recirculation rate of the
liquid smoke was lowest at the start and increased gradually
throughout the run, correlated with a build-up in the liquid
volume, which provided an increasing head of pressure to pump and,
hence, an increased pumping rate. Variation in pumping rate had no
appreciable effect on the results obtained since, as earlier
demonstrated, the liquid smoke yield was the same whether the
pumping rate was deliberately held to its low initial value or
allowed to climb to its highest rate.
The various effects of adopting the "intermediate" aeration level
(about 100 times that in the retort and about one-tenth of that in
the smoke generator) are described in the following paragraphs, the
principal variable or parameter affected being the overall yield of
the liquid smoke product as indicated in the data of Table 7, and
as depicted schematically in the graph of FIG. 3. The aeration rate
in the calciner was varied from between about 9 cubic feet of air
per pound of wood processed to about 34 cubic feet of air per pound
of wood processed. Maximum yields were obtained at about 10 cubic
feet of air for each pound of wood processed.
Table 7
__________________________________________________________________________
Effect of Aeration Level on the Yield of Liquid Smoke Using a
Calciner
__________________________________________________________________________
Run Number 10 6 13 9 14 15 8
__________________________________________________________________________
Aeration Level, cu.ft./lb. Wood 33.4 34 19 17.5 9.1 9.1 10.7 %
Yield of Liquid Smoke (7% Solids) 40.2 44.9 52.9 65.9 76.8 81.8
83.8 % Yield of Charcoal 55.1 52.3 48.0 32.4 24.5 26.4 31.0 %
Residual Volatile in the Charcoal* 59.4 60.3 63.2 39.7 30.0 30.6
54.8
__________________________________________________________________________
*Measured by heating the charcoal 7 minutes at 950.degree. C. to
drive of residual volatiles without burning the charcoal.
As also clearly indicated in the data developed, at the aeration
levels utilized with the calciner the yields of liquid smoke
obtained were significantly greater than the yields obtained
utilizing other equipment and methods. For example, the calciner
yield of liquid smoke was about 12 times that achieved under
conditions producing pyroligneous acid, about seven times that
obtained utilizing the very limited aeration of the retort, and
three times that obtained utilizing the excessive aeration of the
packing house smoke generator. These marked differences are
differences in kind rather than in degree.
Within the aeration range investigated utilizing the commercial
calciner, highest yields were achieved at the lower aeration
levels, possibly because a lower aeration rate permits more
thorough heating and more complete carbonization of the wood. This
is evidenced by a decreased yield of charcoal and lower residual
volatiles in the charcoal. At higher aeration levels it was
necessary to restrict and to limit the heat applied in order to
reduce the danger of open combustion and accompanying ashing of the
wood.
In order to learn what effect the extent of pyrolysis or
carbonization might have upon the quality of the liquid smoke
produced, a series of runs was carried out at a fixed aeration rate
but with different extents of heating to produce 3 different levels
of pyrolysis, each correlated with different yields of liquid smoke
and charcoal. The results obtained are set forth below in Table
8.
Table 8
__________________________________________________________________________
Effect of Degree of Pyrolysis on the Yield and Quality of Liquid
Smoke Run Number 14 17 16
__________________________________________________________________________
Processing Conditions and Products: Aeration Level, cu.ft./lb. 9.1
8.3 8.5 % Yield of Liquid Smoke (7% Solids) 76.8 60.3 39.3 % Yield
of Charcoal 24.5 33.4 63.5 % Residual Volatiles in the Charcoal
30.0 47.1 74.1 Analysis of the Liquid Smoke: % Solids 8.6 6.9 5.1 %
Acidity as Acetic Acid 8.3 7.6 5.7 % Precipitable Solids 0.56 0.15
0.02 Flavor (% of S-10) 133 100 80 Color Factor on Bacon Much
Darker Comparable darker than to S-10 than S-10 S-10
__________________________________________________________________________
Based upon the results tabulated above, it is evident that, with
essentially a fixed rate of aeration, the more thorough the
carbonization of the wood, the higher the yield of liquid smoke
product and the greater the strength of that product, for a given
volume of circulated water. A comparison of the properties of the
three liquid smoke products indicates that, with increase in
carbonization, the solids content, acidity, flavor and color factor
increase. However, precipitable solids undergo a disproportionate
increase as the treated wood nears complete carbonization. This is
undesirable and can be dealt with by diluting the liquid smoke with
water to reduce its strength to the commercially desired 7 percent
solids level. During the dilution step a portion of the
precipitable solids is thrown from solution and discarded, to yield
a final product comparable, in soluble tar content, to the S-10
commercial reference product.
There being no deleterious or objectionable properties or effects
experienced other than indicated above, it is concluded that
complete wood carbonization is a desirable goal of the overall
process, since it affords maximum yields of liquid smoke
product.
The importance of using water as a reactant or extractant in the
liquid smoke generating process was brought out by conducting a run
in which no water was charged to the reservoir of the apparatus and
in which the recirculation pump was left "off." In this work, the
results of which are tabulated below, the generated smoke was
condensed in a tortuous network of pathways or channels in the
packed column and was recovered as a smoke condensate in the
reservoir below. Processing parameters were held fixed, as shown,
with an aeration level of about 45 cubic feet per pound of wood
used, to provide a liquid smoke product yield of 65.5 percent and a
charcoal yield of 35.2 percent, indicating good carbonization. The
properties of the liquid smoked product itself are indicated in the
analysis set forth in Table 9.
Table 9 ______________________________________ Analysis of Liquid
Smoke Made by Condensation ______________________________________ %
Solids 13.0 % Acidity as Acetic Acid 14.0 % Precipitable Solids 2.8
Flavor 500% of S-10 Color Factor on Bacon Darker than S-10
______________________________________
It is evident that both solids and acidity are significantly
increased as compared with the product in which water was used and
recirculated in the packed column. Additionally, the precipitable
solids were found to be at an exceedingly high level, almost 20
times that found in run No. 17 summarized in Table 8. The total
solids were about twice as high, and the flavor level about five
times as great. Finally, and very significantly, a sample of a
product decanted and allowed to settle for 1 week and analyzed for
carcinogens was found to contain about 27 parts per billion of
benzpyrene.
The results obtained in the experiment described point out a
heretofore unrecognized effect of the use of water in conjunction
with the liquid smoke generating process and suggest important
interactions between the liquid smoke and the water in the
absorption column. Specifically, restriction of the aeration to the
pyrolysis zone and elimination of the effective interaction between
smoke condensate and the air introduced into the system results in
the loss of many of the potential benefits of aeration. Exceedingly
high (objectionable) flavor, poor dilutability of the liquid smoke
product, and significant concentrations of carcinogens result. The
investigation suggests that an important part of the effect of
aeration takes place in the absorption column through interaction
of the air with the recirculating liquid smoke.
In order better to compare the smoke condensate (without water
circulation) with the water-absorbed liquid smoke product earlier
described, the former was diluted with water to provide a strength
comparable to the latter. After settling out the precipitated tars
and other insoluble materials, the clear supernatant liquid smoke
layer gave the following analysis.
Table 10 ______________________________________ Analysis of Diluted
Smoke Condensate ______________________________________ % Solids
6.9 % Acidity as Acetic Acid 7.9 % Precipitable Solids 0.1 Flavor
200% of S-10 Color Factor on Bacon Slightly lighter than S-10
______________________________________
While dilution with water was effective to precipitate the bulk of
the "soluble" tars, to provide a product of generally good
dilutability, the high flavor level of the condensate contributed
to a high residual level in the water-diluted product. Moreover,
the color factor content of the latter was low, indicating
deficient color factor production in the original condensate,
probable due to the absence of air interaction as previously
discussed.
The process of the invention is remarkably effective in eliminating
carcinogenic substances from the final liquid smoke product. A
composite sample made by pooling aliquots of the liquid smoke
produced in runs 8, 9, 12, 14, and 15, after allowing the products
to settle for at least 1 week, was examined as a product
representative of the method of the invention. Relevant conditions
of the representative runs were: aeration levels in the range of 9
- 21 cubic feet of air per pound of wood, charcoal yields of from
about 24 - 32 percent (indicating good carbonization), and liquid
smoke yield of from about 63 to about 84 percent. The supernatant
liquid phase was analyzed for benzpyrene, and a second analysis was
carried out on the settled or precipitated tar sample. The results
obtained are significant and conclusive. Whereas the supernatant
liquid product was found to contain 0 parts per billion of
benzpyrene, the tar sample was found to contain 665 parts per
billion. These data support the conclusion that with proper
aeration and recirculation a carcinogen-free liquid smoke product
can be readily prepared, any carcinogens originally present in the
combustion product being effectively separated by the settling out
of the insoluble tars or residues. The latter were found to amount
to from about 7.4-13.6 percent by weight of wood carbonized.
A second composite sample of the calciner-produced liquid smoke
product was prepared by combining the products of 12 individual
calciner runs, allowing 1 week of settling, and then decanting the
supernatant from the precipitated tar residues. The data of Table
11 show the analysis of this lot (No. 26-74) and permit comparison
with the product from the packing house smoke generator (lot
24-86), Table 6, and with the commercial, reference product
S-10.
Table 11
__________________________________________________________________________
Comparison of Calciner-Produced Liquid Smoke to Other Smoke
Products Calciner Liquid Smoke Smoke Range of Pooled Generator
Individual Smoke Liquid Smoke Reference Runs Lot 26-74 Lot 24-89
S-10
__________________________________________________________________________
% Solids 5.1 -8.6 8.2 7.9 8.6 % Acidity as HAc 5.7 -9.9 8.3 7.2 9.9
% Precipit. Solids 0.02-0.56 0.31 0.11 0.33 Flavor (Soup Test)
80-133% 100% 67% 100% Color Factor, Comparable- Darker Darker
Standard on Bacon and much darker than S-10 than S-10 Franks
__________________________________________________________________________
While the calciner-generated liquid smoke product has some
properties which are quite similar to that of the commercial
product S-10, the former exhibits a significantly improved color
factor. As compared with the product from the packing house smoke
generator, the calcined smoke clearly shows the effect of decreased
aeration, namely increased flavor and somewhat increased
precipitable solids. A commercially significant difference is the
improved yield achieved through the utilization of the lower
aeration rate of the calciner.
The present invention establishes the existence of a critical range
of aeration in which the desired properties and characteristics of
commercial liquid smoke are materially enhanced. The present
invention has made possible improved flavor, greater dilutability,
improved color factor content, a complete absence of carcinogenic
material, and increased yields. While the principal work was
carried out using hickory and maple sawdust as the raw materials,
tests carried out indicate that hardwoods such as oak, birch,
beech, and others will serve equally well. It will be appreciated
that a controlled oxygen atmosphere may be used in place of raw
air.
The improved liquid smoke product of the invention represents a
marked advance over not only pyroligneous acid but over other prior
art products as well, including commercial liquid smoke
preparations made using unknown but obviously insufficient levels
of aeration. Finally, the present invention has established a
critical range of aeration which ensures the production of a
commercial product markedly superior to that obtained either at
lower aeration levels or at higher aeration levels.
It will be appreciated that when using different processing
equipment there may be some variation in the precise aeration rate,
etc. which will provide the maximum yield of improved liquid smoke
product. However, in view of the clear teachings of the present
disclosure, and recognizing the criticality in aeration rate as set
forth herein, those skilled in the art will be able, through simple
trial runs, to select the appropriate values for each controlling
parameter involved. Such selection of the optimum aeration rate and
other variables for any particular apparatus will be feasible
without any demand upon or exercise of the inventive faculty.
* * * * *