PRINCIPAL METHODS IN USE FOR PULPING
The chief methods in use for preparing the tomatoes for the cooking
kettle are: first, cold pulping; second, hot pulping; third, crushing
without cycloning.
Cold Pulping
The cold pulping method is probably the most common, and requires less
equipment than the hot method, with results that are considered by many
packers just as good, if the pulp machine is operated by a careful man
who will not feed it too fast, and who will keep it clean. Sometimes,
with this method, the tomatoes are run through a crusher before pulping,
and sometimes not.
Care of Cyclone
It is important that the outlet from the receiving box under the cyclone
be directly from the bottom, and not from the side of the box near the
bottom. The box must drain completely so as not to leave any tomato
juice lying in it to ferment. A tapering enamel lined receptacle which
drains itself completely is best to use under the cyclone.
The steam hose should be turned into both the cyclone and receiving box
several times during the day to arrest growths of micro-organisms, and
clean out adhering tomato fiber. It is particularly important to do this
just before the noon hour, as considerable fermentation can take place
in the cyclone during that hour if it is not cleaned out beforehand.
Hot Pulping
By the hot pulping method the tomatoes are conveyed, usually by means of
a series of “flights,” or a bucket conveyor, to “breaking tanks” which
are arranged above the cyclones. These “breaking tanks” hold about 1000
gallons, and are usually constructed of cypress. At the bottom of the
tank are open brass steam pipes running horizontally in four directions.
These pipes are about two feet in length, and are open at the ends so
that the steam comes directly in contact with the tomatoes. The tomatoes
are conveyed direct from the sorting belt to the “breaking tanks,” and
as soon as the brass pipes are covered the steam is turned on full and
the breaking up process begins. It usually takes about 30 minutes to
break up the tomatoes, and they are then cycloned. The tank should have
a concave bottom and large outlet, preferably 3 inch, so that the broken
up tomatoes can be let out of the tank easily. Iron pipes should, of
course, be avoided, as the acid of the tomato attacks the iron,
producing an iron salt which is apt to discolor the product,
particularly if it is to be used for catsup, and this dissolved iron
comes in contact with the tannic acid of the spices. This will be
discussed further under the manufacture of catsup.
Some packers object to brass and copper coming in contact with the
tomatoes on account of the slight amount of copper which goes into
solution by the action of the tomato acid. In the case of the “breaking
tank,” however, the few short brass pipes offer a very small surface to
the action of the tomato acid, and the amount of metal dissolved would
be negligible. These brass pipes can be plated with tin if it is desired
to avoid contact with brass altogether, and this is frequently done.
Advantages Claimed for Hot Pulping
Those who use the hot pulping method like it for a number of reasons. In
the first place, the tomatoes are brought to a boil while they are still
whole, and this eliminates any chance of fermentation due to the
crushing of the tomatoes before they are cooked. By bringing the
tomatoes to a boil quickly, that is, as soon as the washing and sorting
is completed, any incipient fermentation is arrested immediately. As the
tomato juice is near the boiling point when it is cycloned and delivered
to the cooking kettles, no multiplication of yeasts, bacteria, etc. can
take place between the sorting and the final condensing, unless the
juice is allowed to cool considerably at some point between the
“breaking tank” and the cooking kettle.
Another advantage claimed for the hot process is that the pulp of the
tomato is more completely separated from the seed and skin than when the
tomatoes are pulped cold, and therefore the tomatoes will give a
slightly larger yield of pulp. It is also claimed that a better color
can be obtained by the hot pulping process, as the color cells of the
tomato lie in greatest abundance directly next to the skin, and by
making a clean cut separation of the skin from these color cells by
boiling in a “breaking tank,” none of this color will be lost in the
pumice during the cycloning. Although this argument does appear
reasonable, I have failed to see that tomatoes which are pulped by the
hot process give any better color than those which are pulped cold.
The hot process is also liked where the tomatoes are to be manufactured
directly into catsup or tomato soup, as the “breaking tank” can be
filled up to a certain mark with the boiling tomatoes and that gives the
measure of tomatoes for the catsup or soup batch, and no other measuring
devices for this purpose need be employed.
Objections to Hot Process
The chief objection to the hot process is that it requires a lot of
additional tanks for breaking the tomatoes, which are entirely dispensed
with when cold pulping is used. The tanks are not only an additional
expense to the equipment, but require one or two operators to tend to
them, and they take up a lot of room, and consume a lot of steam. No
seed can be saved from tomatoes which are pulped hot, as the cooking
either kills the germ or renders it impotent. Quite a few canners save
the seed from cold pulped tomatoes, and the revenue from it proves to be
a profitable item.
As to whether the slightly increased yield to be obtained by the hot
pulping method, and the decreased danger of multiplication of yeasts and
bacteria, more than compensate for the advantages to be obtained by the
cold process is a question which the individual packer must decide for
himself.
Crushing
Crushing the tomatoes without cycloning them is a very good method where
the tomatoes are going to be made into pulp or puree, as the finishing
machine will convert the crushed cooked tomatoes into a very smooth
product. Where catsup is to be made direct from the tomatoes, however,
cycloning is to be preferred to crushing. If the final product is to be
soup, cycloning is necessary. This will be discussed further in the
chapters on catsup and soup.
When a crusher is used it takes the place of the cyclone or pulp
machine, although it performs an entirely different kind of an
operation, and the tomatoes go through exactly the same process as in
cold pulping, except that instead of removing the seeds and skins from
the tomatoes before cooking, the tomatoes are chopped very fine and
conveyed to the cooking kettles—seeds, skin and all. It is obviously
somewhat harder to gauge the finishing point of a batch of pulp where
the skins and seeds are present, however a little practice largely
eliminates this difficulty, and there is always the method of
determining the specific gravity by weight to fall back on. The seeds
and skins will not interfere with making the specific gravity test as it
is usually carried out in the cook room with a large copper flask, small
trip balance, and set of weights.
Conveying to Kettle
If the plant is so arranged that the pulped or crushed tomatoes can be
conveyed to the cooking kettles by gravity, that is an advantage, as it
does away with a pump and someone to tend to it, and the fewer the
pumps, the better; however, in most plants it is necessary to pump the
pulped or crushed stock into the cooking kettles. Unless the plant
consists of several floors and the tomatoes start at the top and come
out as finished pulp at the bottom, or the plant is built on a terraced
plan, as one plant is in Indiana, which is built on the side of a hill,
it is necessary to do a certain amount of pumping. An ordinary pump will
not do, as there would be contamination by iron, and considerable
rusting, while the pump was idle, of those parts of the pump with which
tomato juice comes in contact, this rust to be carried along with the
tomato juice the first time the pump is used again. The rotary pump
constructed partly of bronze or nickel is very good for this purpose,
and offers as little opportunity for metallic contamination as any pump
does.
The pipe used for the conveying of this tomato stock should by all means
be enamel lined. Enamel lined pipe, if properly made, will last for many
years without chipping or cracking. Just how long it will last on the
average I cannot say, but I have often taken down lines of enamel lined
pipe that have been in use for several years, and it looked practically
as good as new. The flanged pipe with flanged fittings is better than
that with the ordinary screw ends, as it makes practically a continuous
white tube without any pipe threads in which molds, yeasts, and bacteria
can lodge and multiply.
Wooden troughs are still used in many plants for conveying tomato juice
and pulp, but they are a relic of the old days, and have no place in the
modern pulp or catsup plant. Wooden troughs are hard to keep clean, they
mold very quickly after they become damp, they are open to contamination
from ceilings and roofs which aren’t always in good condition, and they
are usually wasteful. It will pay any packer who still uses even a few
wooden troughs to invest in enamel lined pipe. Wooden pipe is also
unsanitary for this purpose, as mold grows in it and clings so tightly
to the porous, damp surface that it cannot possibly be flushed out.
Value of Pumice
This chapter, which deals principally with cycloning, seems to be a
fitting place to discuss the value of the pumice which comes as a waste
product from the cyclone. Although it has been repeatedly demonstrated
by chemical analysis that this pumice or tomato waste is a valuable
by-product, every time the question has come up of its utilization and
preparation into a salable product or products, the decision has been
that the expense involved would be too great to make it pay. This
by-product is profitably handled in Italy, producing an oil of
commercial value, and an oil cake which is used for stock feed; however,
the conditions in Italy and in this country are very different. In the
Parma district of Italy there are forty factories very close together,
and little expense is involved in bringing the waste to a central point
where enough of it can be had to keep a drying outfit and an oil press
or oil extraction outfit busy. Labor is also very cheap and plentiful,
and there is a ready market for the product, the oil being used as a
soap stock, and the oil cake finding ready sale as a stock feed. In this
country, however, there is not enough waste at even one of the largest
plants to pay for the operation of a drying outfit and the pulp plants
are so scattered that hauling or shipping charges to a central point
would be expensive. Furthermore, labor is scarce and expensive.
That quite a little labor is involved in the preparation of the waste is
soon discovered by a little experimenting. As the waste ferments quickly
it must be handled as produced, or preserved in some way, which would be
a questionable operation, as the oil cake is used for stock feed. As the
skins are practically valueless, they must be separated from the seeds
in which all the value lies. This separation can either be carried out
in the moist state by a gravity separation in water, in which the seeds,
being heavy, sink, and the skins float; or by the use of a fanning mill
after drying, in which case the dried skins, being very light, are blown
out. Before drying either the seeds alone or the unseparated waste, the
excess moisture must be pressed out with a hydraulic press. The pressed
product must then be broken up and put through a steam or hot air dryer
of the rotary, cylindrical type. After the seeds are dried to a 10 per
cent moisture basis they must then be ground, and the oil extracted
either by pressure, or by dissolving it out with a chemical agent, such
as carbon tetrachloride. The oil cake which remains would then be sacked
for stock feed.
This briefly gives an idea of the labor involved, and the difficulties
surrounding the situation. It may be successfully worked out some time,
but will require close co-operation from a number of large pulp plants
which are near each other to be a success. Some plants are giving the
waste to farmers if they will haul it away, and I know of one farmer who
has for years fattened a bunch of hogs cheaply during the tomato season
in this way. It is a queer thing, though, that most farmers turn up
their noses at the idea.
The seed, when dried to a 10 per cent moisture basis, contains about 23
per cent protein and from 20 to 25 per cent of fat. After the fat is
extracted the protein in the cake will run close to 30 per cent.
In a test made by the U. S. Department of Agriculture the ground cake
ran 37 per cent in protein, which puts it in about the same class with
cottonseed meal. They also refined some of the oil and are of the
opinion that it has the qualities of an edible oil.
If a factory uses the cold pulping method the most profitable way to
handle the pumice is to ferment it and then separate the seed and dry
it, and use it for planting the following season. Care must be taken,
however, to keep out undesirable strains and varieties foreign to the
one which is being grown.