Tomato pulp is the fleshy portion of the tomato separated from
skins, cores and seeds by means of a fine mesh screen and suitably
concentrated by evaporation.
During recent years great improvements have been made in the
manufacture of tomato pulp and in the quality and appearance of the
product. The care exercised in the selection of the raw material and in
all steps of the manufacture of tomato pulp has been greatly increased.
This is equally true of pulp marketed in small cans to be used as soup
stock in private homes and of the pulp sold in larger containers for
the manufacture of soup and ketchup. The large buyers of pulp have
determined the grade or quality which gives them the best results in
the manufacture of other products and the degree of concentration
which they can use most economically. It is now customary, therefore,
for large sales of pulp to be made on specifications, and it is
impracticable to comply with such specifications without carefully
controlling the manufacture of the product. The raw material must be so
selected and the manufacturing operations so controlled that the color
and flavor of the finished product is conserved. This is discussed
briefly on page 7.
If he desires to sell under specification, the manufacturer must comply
with his contract with respect to specific gravity, and he cannot
greatly exceed the specific gravity specified without substantial
sacrifice in cost of manufacture. It is therefore economical to
determine the specific gravity of the product as accurately as
practicable (see p. 51) and also to adopt methods of manufacture
that will control as closely as possible the specific gravity of the
finished product.
Beginning on page 33, methods are given for the determination of
specific gravity under various conditions of manufacture and sale,
and on page 50 is given the method for the determination of specific
gravity of the cyclone juice or partly concentrated pulp which this
laboratory has suggested as an aid to determining the volume to which
the product should be evaporated to secure the desired specific
gravity. This method has been used by a number of pulp manufacturers
and found to be relatively convenient and practicable. It might be
used to better advantage and to considerably greater profit if more
help were employed—and some times more competent help—in determining
specific gravity and controlling the point at which evaporation should
stop.
The importance and economy of accuracy in the determination of specific
gravity is not fully appreciated by all, though some of the larger
manufacturers are now giving much attention to that subject. This
matter is discussed on page 50.
There is included in the bulletin beginning on page =13= a detailed
description of the Howard method for the microscopic examination
of tomato products, and following that a detailed statement of the
chemical and physical methods employed in this laboratory for their
examination. Such methods are only of value to those trained in
laboratory work. They are included here because the laboratory receives
many requests for these methods from chemists employed by manufacturers
of pulp. Men who are employed only for the tomato season find special
need for such information.
Our correspondence brings many inquiries regarding the percentage of
solids in pulp of different specific gravities, and also regarding the
relative values of pulp of different specific gravities. In Table 10
(p. 59) there is given in parallel columns the specific gravities of
pulp of different degrees of concentration and corresponding percentage
of solids, and it is a simple matter to calculate the volume which the
same pulp would make if concentrated to any other specific gravity.
This calculation is explained on page =54=—in discussing the point
at which to stop evaporation to secure pulp of any desired specific
gravity.
This bulletin supersedes Bulletins 3 and 7, and also contains material
which has appeared in several trade-paper articles prepared in this
laboratory. These articles are extensively quoted and some of them
are printed almost in full. Dr. F. F. Fitzgerald was the co-author of
most of these publications and did much of the work on which they were
based. He is therefore entitled to a substantial share of the credit
for the material in this bulletin.