Allen Paul W. Industrial Fermentations

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FOOD PRESERVATION PROCESSES 211

cold storage food and fresh food as there is between condensed milk

and fresh milk. We can sum up the situation by saying that a normal

phenomenon happens to foods under normal conditions while an ab-

normal action is sure to follow when the food ia placed under abnormal

conditions. There is no commoner illustration of this than the fact

that milk under normal conditions spoils because of the lactic acid fer-

mentation of Bact. lactis acidi but when the same milk is held at low

temperatures the lactic acid fermentation disappears and in its place

there may occur other kinds of decomposition of a less harmless nature

than the changes caused by the lactic acid organism.' However, this

viewpoint does not argue against cold storage or any other kind of

food preservation. The economic situation demands that cold storage

be more and more extensively practiced. As population becomes

denser fluctuations in production and consumption of food are bound

to become more extensive.

In the preservation of eggs, meat, and dairy products we have

perhaps the greatest problems of cold storage. But with the bacteriolo-

gist it is not a question of advocating a decrease in the practice of cold

storage, but of solving the problems of cold storage and counteracting

the weak points in the practice. We have in this subject a good

illustration of how the science of a process follows many years behind

its practical application. For instance, cold storage of dairy products

to a considerable extent began in 1876 but studies concerning this

practice were not carried out until recently.

"There are many commercial illustrations of the problems resulting

from a few degrees difference in the storage of food but there is none

more unique than that worked out by Thorn in connection with Cam-

embert cheese. He showed that the flavor of Camembert cheese is

probably due to the associative action of Odium lactis and P. camem-

berti and that the change of a degree from the storage temperature

would allow one organism or the other to forge ahead of its associate

and spoil the cheese.

Cold may act as a preservative in two different ways, either by

retarding growth or by actually bursting the bacterial cells. To explain

how cold or in reality the absence of heat energy retards growth would

be to explain the mechanism of growth in general. This is on the

border line of our present knowledge or probably considerably over

the border, however, Kruse gives a few ideas on this subject. He

says that growth in bacteria is a combination of syntheses and that

these syntheses result in the formation of cell substance out of common

food materials. This is well illustrated by the assimilation of carbon

dioxide by the nitro-baoteria in the absence of light and chlorophyll

and by a similar process of certain sulphur bacteria. The process

and the mechanism of syntheses is not understood but our recently

acquired knowledge of fermentation indicates that the building up

of protoplasm, that is, growth, is due to the power of particular

enzymes'. Assimilation and dissimilation may have the same mech-

anism. Kruse says that it would be unwise not to consider these

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possibilities. For years the idea was considered unacceptable that

the phenomena of dissimilation occurred within the living cells through

a special enzymatic material formed by the cells and which could not

be isolated because of its delicate nature. In recent years

, however,

the zymase of alcoholic fermentation and the enzymes of lactic acid

and acetic acid fermentations have been isolated.

If we accept this explanation of the mechanism of growth it be-

comes easy to see how low temperatures are preservative but it would

follow according to this theory that the lower the temperature the

less the growth for any particular organism. This may be true.

The multiplication of B. coli at different temperatures illustrates

very well how bacteria have a certain temperature range within which

they grow.

The generation time of B. ooli according to Russell is as follows:

46 degrees

35 "

26 "

20 "

16 "

10 "

TABLE

113 degro

104 "

95 "

86 "

77 "

68 "

60 "

50 "

VI.

88 F.

20 minutes

172 "

22 "

26 "

96 "

120 "

14 bra. 20 minutes

Many bacteria have a range of growth much narrower than the coli

group and when we consider that some bacteria grow at temperatures

between 70 and 80 degrees C, a temperature which coagulates albumin

and a minimim) temperature of above 30 degrees C. then we can

appreciate that there are also organisms which grow best at tempera-

tures below zero.

In the case of most bacteria there is a destruction of bacterial cells

when the storage temperature is low enough to freeze them as the intra-

cellular fluid in freezing expands and bursts the cell walls. The amount

of preservation due to this phenomenon is not considered so very

important.

The three different temperatures which are largely used in storing

dairy products are 10° C. for storage of milk and oream which cannot

be frozen; 0° C. for frozen milk, a product shipped somewhat in

Europe; and —9° C. for storage of ice cream and butter. Tempera-

tures below —9° C. are used mainly experimentally.

The effect of freezing milk on oreaming, churning, and upon the

quality, according to Hills and Kirby, is very slight. In freezing

.milk the fat freezes out at first and remains in the liquid portion ac-

pording to Farrington. He says that when about 25% of the milk is

frozen the fat content of the liquid portion rises about .5%. On the

other hand, the casein, milk sugar, and ash was not separated to any

great extent by freezing. Marshall erays that milk and butter must not

be frozen in order to stop bacterial growth completely but that enzymic

FOOD PRESERVATION PROCESSES 213

action does not neoessarily stop when milk or butter are frozen.

Deterioration of these products may take place slowly although these

products are frozen.

In 1895, a patent was taken out by a Swedish engineer for frozen

milk for shipment, and according to some reports the practice was

very successful. Frozen milk was shipped from Gothenburg to London

in large pine barrels containing about 1200 lbs.

Siegfeld analyzed samples of this frozen milk and found the upper

portion of the block contained 8.45% fat, the lower portion 2.11%

fat, and that the total solids increased toward the center of the cake.

Ice cream manufacturers keep their ice cream below —9" C. in

order to maintain its stiffness. The ice cream hardening room is kept

at —32° F. as nearly as possible, although the moving in of new

batches of ice cream has a tendency to raise the temperature a degree

or two.

In the cold storage of fruite it is essential that the conditions of

temperature, ventilation, and moisture be adapted to the fruit stored.

Practically all fruits have special kinds of microorganisms which

they must be protected against. Wrapping fruit is a special protection

against spread of fungi in, a storage cellar and will help to prevent

wilting.

It is impossible to prevent the process of ripening in fruite but it

is possible to slow it up. The best temperature at which to hold the

cellar is that just above what causes freezing of the fruit.

The same factors which must be regulated for fruit must also be

regulated for vegetables. However, different vegetables have their

special temperatures and humidity conditions at which they should be

Btored. For instance, squash should be stored at 50° F. while potatoes

are stored best near the temperature of freezing.

The storage of apples for shipment has grown to enormous pro-

portions in recent years' due to better knowledge of the factors of

storage and to better shipping f acilities.

H. J. Ramsey says, "For a proper understanding of the behavior

of apples in storage it must be kept clearly in mind that the apple, like

all fruits', is a living organism and that its life cycle, which begins in

the blossom, ends under natural conditions in the death and dec^y of

the fruit. The function of cold storage is primarily to retard these life

processes."

It should be added further that as the life cycle of the apple pro-

ceeds after maturity of the fruit there is less and less resistance to

the attack of molds, yeasts, and bacteria. By many 32° F. is con-

sidered the most favorable temperature at which to store apples'.

The organisms attacking apples in storage are both parasitio and

saprophytic.

The practice of freezing meat for its storage and shipment was

originated by Tellier, a Frenchman, according to Melvin. He says:

"The only South American countries exporting refrigerated meats

are Argentina and Uruguay. The large exporting establishments are

214 INDUSTRIAL FERMENTATIONS

situated mostly on the River Plate, and the frozen and chilled meats

are in most cases loaded directly into the ocean steamers. The export

trade in refrigerated meats owes its beginning and development to the

invention by a French engineer, Charles Tellier, of a system for pre-

serving fresh meats by refrigeration during the time required for the

ocean voyage from South America to Europe. The pioneer steamship

in this trade, Le FrigorifiqiLe, constructed with refrigerating facilities

according to the Tellier system, made a successful trial voyage with

fresh meat from Rouen, France, to Buenos Aires in 1876. In the fol-

lowing year this vessel and Le Paraguay began the transportation of

frozen meat from Argentina to Europe under the respective manage-

ment of two French firms, the Tellier and Jullien Companies, which

were given a five-year monopoly by the Argentine Government."

Preservation o£ Chickens by Cold Storage.

M. E. Pennington in U£D.A. Yearbook (1907) says:

"Although it is impossible to obtain exact statistics on the subjeot,

it is estimated that approximately from 75 to 90 per cent of all the

poultry produced in the United States is, for a longer or shorter period,

preserved in cold storage. While the number of ducks, turkeys, and

geese is by no means small, ohickens, of course, are greatly in the

majority, and from the appearance of the cold-storage warehouses in

our large oities it would seem to be almost a matter of routine that

every chicken intended for market should sojourn there for a certain,

or rather an uncertain time.

"The storage of eggs for preservation by cold is almost exclusively

confined to the early spring and summer, .since at this time they are

most plentiful. The placing of chickens in cold storage, on the con-

trary, may oocur at almost any season, the large poultry raiser killing

the birds of the age desired and shipping them to the warehouse, to be

sold when the market is most lucrative. At certain seasons, however,

practically clean sweeps will be made in the country adjoining large

cities of all the birds suitable for market, so that for weeks afterward

it is impossible to purchase fresh chiokens. This is most apt to occur

in the case of stewing and roasting ohickens in early summer, when the

broilers are well advanced and it is desirable to weed out all un-

profitable laying hens and superfluous cocks. Hence, in the early

summer the purchaser of any except broiling fowls is very likely to get

those which nave been in storage.

Temperatures Used in Cold Storage of Chickens.

"It is generally conceded that the freezing of the fowl should be

as prompt as possible, therefore some warehouses place the chickens

for a few hours at —10 degrees F. (—23.33 degrees C), transferring

them, when frozen, to a temperature of about 16 degrees F. (—9.44

degrees C.) for permanent storage. Others use the latter temperature

FOOD PRESERVATION PROCESSES 215

exclusively, while there are those who prefer 18 degrees to 2z degrees F.

(—7.78 degrees to —5.55 degrees C). The New Zealand Department

of Agriculture supports the latter view, and its report states that

such delicate tissues and small bodies as are found in the case of

chiokens lose their bloom and contract when kept at 15 degrees F. or

below. However, it must not be forgotten that the birds so.stored are

far more carefully handled and selected than are the promiscuous lots

shipped to our storage warehouses. De Loverdo advocates —5° F.

(—20.6 degrees C.) for freezing and 15 degrees F. (—9.44 degrees C.)

for maintenance, though he states that in consequence of such rigorous

temperatures the tissues contract and lose their elasticity.

Method of Thawing,

"Another factor in the final condition of the salable cold-storage

fowl is the method of thawing. If the bird direotly from the freezer

be exposed to air at the usual temperature there is likely to be a

condensation of moisture on the outer surface and a consequent de-

generation of the tissue and often a growth of molds. Hence, it is

necessary to thaw in a current of dry, cool air if thip method be

adopted. The most common practice is simply to place the birds in a

vessel of water at room temperature. An appreciable amount of water

is absorbed by the dried meat, thereby adding to the prioe received,

since it is sold by weight and, to the householder at least, the chicken

is sold in a thawed condition. Acoording to the warehouse men the

best results are obtained when the frozen birds are packed-in small

pieces of ice and more than twenty-four hours allowed for thawing.

Appearance of Chickens Stored for Varying Periods.

"While conducting certain investigations concerning the changes

taking place in foodstuffs when preserved by cold, it has been necessary

to examine a number of chickens stored for periods varying from a

few days to several years. Contrary to the statements generally made

by the trade, there have been noted marked differences between fresh

and cold-storage chickens, which differences are apparently progres-

sively dependent upon the time of storage. Even after very short

periods oi storage in a solidly frozen condition, microscopic examina-

tion reveals changes in the muscle fibers."

In discussing a chicken stored for three years M. E. Pennington

says:

"The most striking difference between this chicken stored for three

years and those stored for shorter periods or those which are fresh

is this pronounced inflexibility and the general green tint of the pkin.

The whole appearance of the bird was unpleasant in the extreme. Hie

odor was not that of putrefaction, but was of a sharp, penetrating,

unpleasant character having a biting property, which suggested the

effect of acrolein on the eyes and nostrils. While this was plainly de-

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INDUSTRIAL FERMENTATIONS

tected in the unopened bird, the muscles and the viscera gave it far

more distinctly, and a decided increase in its intensity was noticed

while the study was progressing.

"The texture of the p>in was such that its original oharacter

would have never been surmised. Every partiole of elasticity had

vanished and its appearance was that of dirty, green, wrinkled parch-

ment. The feather papilla were seen only as rather darker areas.

Where the sVin was stretched over the bones it was exceedingly thin

and with very little pressure would crack. This fact is illustrated by

the bare breast and the projecting appearance of the leg bones, the

qirin having split on the breast and being ready to split over the folded

joints.

The eyeball was much sunken, while the comb and gills had

practically disappeared.

Muscles and Internal Organs.

"In the case of ohickens which had been in storage three years

the

changes in texture and color of both muscles and fat were especially

striking. There was a very marked drying out, particularly of the

muscles of the upper breast, so that the larger portion of them had

become as parchment-like in character as was the skin and might

easily have been mistaken for the skin

itself.

Below this yellow-tinged

dried area the breast musoles presented almost a rust red. The gradual

paling of the thin muscle as noticed in the fresh chicken was entirely

wanting. On the inner part of the thigh, the soft salmon pink of the

fresh muscle was replaced by colors varying from a deep brown to

bluish red, and there was no trace of the original color to be dis-

tinguished. Between these muscles the bands of shrunken fat were of a

deep brown orange color. No feature of the entire chicken was more

striking by comparison with the fresh fowl than this change in the

color of the fat.

"There was also noticed in this chicken, unlike those which had been

previously studied, a very distinot indication, by the discoloration of

the abdominal wall, that the viscera had not been removed.

"Clipping through the hardened fibers of the pectoralis major

and exposing thereby the pectoralis minor, its fibers were seen to be

almost, if not quite, as dried out as were those of the outer muscle."

The Preservation of Fresh Caught Fish During Transportation.

M. E. Pennington says: "As a general rule the dominant fish in a

market are produced comparatively near by. The catch of the Atlantic,

for^ example, stays almost entirely east of the Alleghenieff, except that

which is canned or otherwise preserved, which, of oourse, goes all

over the country and is exported. The Gulf and the Lakes and the

Mississippi supply the interior and ship but little over the eastern

range. The Pacific coast, on the other hand, sends two staple varieties

of fish throughout the country, namely, halibut and salmon. These

fish are sent (on express schedule) across the continent in carload lots,

FOOD PRESERVATION PROCESSES 217

paoked in fine ice, and constitute, with red snapper from the

Gulf,

most of the salt-water fish supply of the interior. The distribution

of Pacific salmon and halibut extends also to the Atlantic coast cities,

which are heavy consumers. For some of our fish we are sending to

Canada. Smelts, lobsters, and salmon come to us in quantity from

Canadian waters, as does also much of the "winter caught" fresh water

fish. The latter are obtained by cutting a series of holes through the

ice,

stringing gill nets from hole to hole, and pulling the nets up through

the holes to remove the catch. This fishing is done when the tem-

perature is below the freezing point, sometimes at 40 degrees below

zero,

Fahrenheit, and the fish are, therefore, frozen almost immediately

upon their removal from the water. They are boxed and held on the

ice until hauled by teams to refrigerator cars and so shipped to cold-

storage plants in cities. The unparalleled freshness of low temperature

weather frozen fish, even after months of storage, is a strong argument

for the installation of fish freezers as near the source of production

as possible.

"The eastern coast markets carry the following staple varieties,

which may be had the year around:

STAPLH VABIETIHS OF FISH.

Salt-Water

Fish

Bluefish

Cod

Pollock

Porgies

BOUD

Flukes or flounders Salmon, western

Haddock

Hake

Halibut

Herring

Mackerel

Sea bass

Smelts

Shad

Weakfish

Whiting (silver hake)

Fresh-Water Fish

Ciscoes (lake herring)

Lake trout

Whiteflsh

German oarp

Buffalo oarp

"It must be remembered that winter fishing is of but small mo-

ment. Most of the fishermen tie up when winter comes and do not

ply their trade until spring. Fortunately for the stability of tie

markets, but even more fortunately for the supply of food, the prac-

tice of freezing the excess summer catch and holding it at temperatures

close to zero Fahrenheit until winter time, has become so general that

from October 1 to April 30,- which mark the limits of the storage-

stocks season, we have a continuous course of fish in excellent order

from the warehouse to the market to be disposed of, generally, at

lower prices than the fresh-caught article.

"The foreign-born population in the congested areas of our large

cities are not prejudiced in favor of certain varieties; provided the

price is within their means the name of the fish is a secondary matter.

And if the fish is palatable the fact that it is hard frozen does not

weigh against a low price. Consequently, we find hard-frozen whiting

and other plentiful fish selling for a few cents a pound in inland

towns as well as on the coast, when the shops in the residence districts

are charging double the price for the same article thawed to simulate

218 INDUSTRIAL FERMENTATIONS

fresh-caught fish and sold as fresh, a condition directly traceable to

the ignorance of the consumer."

III.

Food Preservation by Drying.

Preservation of food by drying is one of the most primitive

methods of preserving. Nevertheless, its importance in modern food

preparation is being more and more emphasized due to the fact that

the natural flavors of many fruits and vegetables are best retained

by this method of preservation. With the coming of knowledge of

vitH.minp.fl and food accessories, there seem to be additional ad-

vantages gained by this method. The variety of food which can be

successfully dried has been greatly enlarged in the^ last few years

and efficiency of drying apparatus has been greatly increased. Some

of the food products which are speoially adapted to drying are:

(1) Apples

(2) Peaohes

(3) Berries at 126° F.

(4) Cherries

(5) Apricote

(6) Pears

(7) Com between "milk" and "dough" stage

(8) Eggs

(9) Milk

(10) Buttermilk.

In differentiating between dried and evaporated fruit Caldwell

says:

"The terms 'dried fruit' and 'evaporated fruit' are popularly

used to designate all fruits preserved by reduction of their moisture

content to such a point that spoilage does not ocour. In the trade

the term 'dried fruit' is applied to any produot in which moisture

reduction has been brought about by exposure of the fresh material to

the heat of the sun, while products made by driving off the surplus

moisture by the use of artificial heat are known as 'evaporated' fruits,

less frequently as dehydrated or desiccated fruits. While the pro-

cesses of sun drying and drying with artificial heat in evaporating

devices are widely different, the differences in the quality of the prod-

ucts

obtained are relatively slight, it is possible to apply both processes

to any of the fruits ordinarily dried, and the extent to which one or

the other method is employed in preserving any given fruit is de-

termined by the climatic conditions prevailing during the period in

which the drying must be done. By reason of the possession of an

exceedingly favorable combination of dry atmosphere, continuous sun-

shine, and practical absence of rain or dew during the drying season,

California has developed sun drying on a large scale and is the only

State which has done so."

Caldwell further says: "The purpose in view in drying any food

material is to reduce its moisture content to such a point that the

FOOD PRESERVATION PROCESSES 219

growth of organisms therein, will no longer be possible, and to do

this with a minimum of alteration in the food value, appearance, and

palatability of the product. The necessity for avoiding -changes in

physical appearance and chemical composition, other than actual

loss of water, puts very definite limitations upon the means which

may be employed to bring about drying and makes an understanding

of certain principles a prerequisite to successful work."

Concerning tiie type of evaporator to be used in drying fruit Cald-

well says: "The kiln evaporator is designed especially for the handling

of apples in large quantities, and iff more widely used for that purpose

than all others combined, but it is not well adapted to the drying of

«=7

4*w£w-

'•—A section through, the-tunnel drier.

After OaldwtU in TJAJ)A, Bulletin 1HL

Fia. 83.—The prune tunnel evaporator.

other fruits. For thin reason, the building of a IHIn evaporator in a

district which is devoted-to general fruit growing would be ill advised.

The prune tunnel evaporator, on the other hand, is a general-purpose

evaporator which may be employed for drying other materials as well

as apples and is consequently better fitted to the needs of a farm or

community which may have occasion to dry peaches, prunes, berries,

or other fruits. For this and a number of other reasons, which will be

pointed out in a subsequent section, a tunnel or modified tunnel drier

should be built wherever a community drying plant is needed.

The Kiln Type.

"Cast-iron, hard-coal furnaces are universally used in apple kilns

throughout the Eastern States. These furnaces have a grate of 5 to 8

!20

INDUSTRIAL FERMENTATIONS

iquare feet and are capable of supplying heat for a standard 20 by

JO foot kiln. Such furnaces are of very heavy construction, weighing

.,500 to 1,800 pounds, and consequently they maintain a fairly uni-

orm temperature with only occasional attention from the fireman.

The products of combustion pass through sheet-iron pipes arranged in

ows under the floor and finally into the chimney.

After Russell

VJ3J)J..

Bulletin

1131.

Fia. 34.—Plant of a oommeraal-siae drier in perspective. The arrangement

the trays ia Bhown in one compartment. The aide roof on the right is not

wn.

"Several individual kilns constitute a drying plant. As it is

iessary to have enough drying capacity to keep the machinery and

p employed, the number of kilns in a plant varies, but economic

^derations would generally forbid the construction of a plant

ing less than four kilns, since installations of power-driven equip-

it in a smaller plant would be almost as expensive as in a four-

plant. A plant of this size is large enough to keep the operators

y, and plants larger than this increase the fire risk without add-