16 BULLETIN 1265, U. S. DEPARTMENT OF AGRICULTURE 
of the peas, the character of the water used, and the length of the 
processing period. Under the conditions of these experiments, peas 
suitable for canning purposes always yielded an agreeably soft 
canned product except in those cases where lime or other chemicals 
were used. Careful scalding will not make peas of mixed grades 
equally tender. Hard peas will require longer cooking than young, 
tender ones, whether cooking is done in the scalding process or after 
putting into the can, and a precook timed to render the hard peas 
tender will overcook the younger peas with which they are mixed. 
Accomplishing uniformity in the canned product, as far as softness 
is concerned, depends upon the efficiency of the grader and processor 
rather than upon the scalder. 
The fact that the softness or hardness of the water used in the 
packing of peas and other vegetables has a very important bearing 
upon the tenderness of the product is quite well known, and Huen- 
ink and Bartow (33) have made this a matter of careful study. 
According to these workers, the presence of the chlorides and sul- 
phates of calcium and magnesium is especially important in causing 
the hardening of canned foods. Hardening due to the use of lime 
salts in some of these experiments has already been mentioned. 
The reason for the hardening of the peas and other vegetables in 
hard water seems to be the union of calcium and magnesium with 
the pectic substances of the middle lamella?, forming relatively in- 
soluble calcium and magnesium pectates. The other alkaline earth 
metals act similarly. The use of sodium carbonate and the car- 
bonates and hydroxides of the other alkali metals causes a soften- 
ing, due largely to their action upon these pectinlike materials. 
MUCILAGINOUS SUBSTANCES ON PEAS. 
Numerous writers (see reference, p. 43) have called attention to 
the presence of mucilaginous, mucous, sticky, or gummy substances 
on the surface of certain vegetables, especially peas, and have con- 
sidered scalding necessary to remove this objectionable material. 
Many years of familiarity with green peas, in the field, the kitchen, 
and the laboratory, make it difficult for the writers to understand 
how such properties should have been ascribed to fresh green peas. 
There is scarcely anything that grows in the garden that is more 
nearly free from mucilaginous or sticky substances than fresh green 
peas. Microscopic examination shows that the outer portion of the 
pea has a highly cuticularized surface, which is chemically the 
most insoluble portion of it. When the peas are shelled by vining 
machines, which are used in modern commercial canneries, the peas 
may be more or less sticky as they come from the machine, due to the 
coating with juices from the vines and pods. If allowed to stand 
for some time in large quantities, natural respiratory processes cause 
a rise in temperature, and the bacteria, which are present in the juice 
as a result of the introduction of dust during the vining process, 
begin to develop. Through the action of these bacteria, the sticky 
or slimy condition may become such as to greatly impair the quality 
of (lie peas for canning purposes. 
In home canning, on the other hand, sliminess is never encountered 
unless (lie pens have been allowed to stand in considerable quantity 
lor some time. Sliminess here indicates that bacterial action is well 
under way, and that slack methods of handling have been followed. 
