During the height of the season, it may not be possible to convert all
the tomatoes directly into ketchup, in which event the surplus may be
made into pulp. The first part of the operation is identical with that
already described. The concentration is carried just far enough so that
subsequently by slow heating for spicing it will give the proper
consistency when made into ketchup. A standard has not been fixed, but
tentatively it has been proposed that it be at about a specific gravity
of 1.035. The concentration may be carried further and water added at
the time of the final cooking, but when this is done, the resultant
product does not have the same smooth consistency that is obtained by
using the thinner pulp. Heavy pulp is made for the purpose of
economizing in cans, but experience has shown that economy does not
always follow. The higher the concentration, the higher the acid
content, and this may attack the enamel and metal with resulting bitter
flavor and frequent pinholes. Some manufacturers who prepare their own
pulp carry the concentration between 1.030 and 1.033. The method of
obtaining this density is to use flasks graduated to hold 500 or 1000
grams of water at 200 degrees F., fill them with the hot pulp and weigh
at once. For each flask there should be a proper counterpoise, and the
balance be sensitive and weigh in grams. If the 1000-gram flask be used,
the specific gravity will be the same as the weight of the pulp. With a
valve funnel the flask may be filled level full and the weight taken in
less than thirty seconds. For cold pulp, a similar flask is used, but
graduated at 60 degrees F. and after filling, the flask is set in a
sling and whirled a few times to free it from bubbles, filled again to
the level, and then weighed. For pulp of a specific gravity of less than
1.037, this gives fairly concordant results, but the errors increase
rapidly the higher the concentration. The same methods may be employed
on ketchup. Recently, W. D. Bigelow has improved the apparatus by using
a copper flask and adding a handle by which the flask may be submerged
in the kettle to take the sample and thus prevents the entrance of air.
The use of flasks of any size is described in Bulletin No. 3, National
Canners’ Association.
The use of the specific gravity method only partly solves the question
of standardization. Two pulps each of 1.035 may vary considerably in
what the chef terms body and there is no method of accurately measuring
this factor or expressing it. Pulp made by draining will be lighter in
weight with the same body, and that from skins and cores will be rough
or have the appearance of separating into small flakes or lumps. The
specific gravity bears a close relation to the soluble solids, and as
these do not have a constant ratio to the fiber in whole fruit, and as
the ratio is further disturbed by drainage and in the use of trimmings,
it is obvious that the method will not give an exact standard.
Pulp should be filled into gallon or five gallon cans as hot as possible
and sealed at once. The practice followed by some manufacturers is to
steam the cans first, then depend upon the heat in the pulp to
sterilize. The cans are allowed to stand hot for forty minutes, then
cooled. The other practice is to give the hot cans a process of about
twenty minutes for gallons, forty minutes for five gallons, and then to
cool. Cooling is essential to retain color and flavor, as prolonged heat
causes “stack burning,” producing a brownish color and a bitter taste.
The highest grade pulp can not be held in barrels for the reason that
the heat is retained too long. Stack burning will take place in glass if
the packages are not allowed to cool well in the air before being
stored, though the changes are not so marked as in the tin.