Ketchup is defined in the Federal food standards as the clean, sound
product made from properly prepared pulp of clean, sound, fresh, ripe
tomatoes, with spices, and with or without sugar and vinegar.
The solid matter, or total solids, in ketchup varies from less than 12
per cent to over 37 per cent. This means that the product varies from
a substance having barely sufficient tomato added to give color and
taste, to a rich, heavy tomato ketchup. The variation of total solids
in any one brand is, of course, less, but large differences are not
unusual. Three bottles of one brand showed a solids content varying
from 12 per cent to 16 per cent, and seven of another brand varied from
32 per cent to 37.2 per cent.
The amount of solids in a non-preservative ketchup should be not
materially less than 28 per cent. It is necessary to have a rather high
solid content for ketchup of this kind, so that it may keep after being
opened on the consumer’s table.
The variation in the insoluble solids is comparable to that in the
total solids. The values for a number of samples examined in this
laboratory ranged from .9 per cent to 2.3 per cent. As the insoluble
solids come from the tomato pulp the amount of insoluble solids is to
that extent an indication of the amount of tomato pulp used in the
manufacture of the ketchup from whole tomato pulp. The consistency of
the ketchup is dependent chiefly on the amount of insoluble tomato
solids present.
The ash usually varies from 2 per cent to 4 per cent, owing to the
different amounts of salt, which varies in general from 1½ to 3 per
cent.
The acidity ranges from .4 to 2.3 per cent. The acidity is one of the
most important factors in preventing the growth of bacteria and yeasts
in the ketchup after being opened. In order to secure the best results
the ketchup should have an acidity of over 1 per cent (expressed as
acetic acid) and an acidity of 1.25 per cent or higher adds to the
keeping quality of the ketchup after the bottle is opened. An increase
in acidity will necessarily require an increase in the amount of sugar
in order to secure the proper flavor; or, vice versa, an increase in
the sugar will necessitate an increase in acidity. In some ketchups
about one-half of the acidity is due to the citric acid of the tomatoes
and the remainder to the vinegar added in manufacture. With ketchups of
exceptionally high acidity, the proportion of citric acid to total acid
may be much less than this. There may be considerable difference in the
acidity in ketchup of the same brand due to variations in manufacture.
The sugar present in the ketchup is derived both from the pulp and
from the added sugar. In ketchup ranging from 12 to 30 per cent total
solids, from 9 to 22 per cent of the solids may consist of sugars.