SCALDING, PKECOOKING, AND CHILLING 37 
full pack which the increase in flexibility made possible, and the 
lessened strain on cans. 
To reduce strain on cans, and get the proper vacuum, a separate 
operation, known as exhausting, is generally practiced. Exhausting, 
ordinarily, is done by heating the cans for a short time just before 
sealing. Scalding and exhausting are, therefore, the same in prin- 
ciple ; one consists of heating material before putting it into the can, 
and the other of heating after it is put into the can. The vacuum 
obtained depends on the temperature of the material at the time of 
sealing. When the scalded material is filled into the cans while hot 
and sealed immediately exhausting may not be necessary. With 
some food substances scalding may be unnecessary, if the exhausting 
is done. In many cases, if not most, one operation or the other may 
be eliminated with a saving of time and cost. 
Plunging freshly scalded material into cold water, because of the 
lowering of the temperature, makes an exhaust necessary, which 
increases the labor cost of canning. There are times, as in the 
peeling of tomatoes, when this practice is justified, but the general 
application of it to- all canned materials seems unwarranted to the 
writers. 
GENERAL SUMMARY. 
In the preparation of fresh vegetables for canning, a preliminary 
scalding, in most cases, results in a greater or less reduction in bulk, 
due to loss of turgiclity of the tissues and the expulsion of air. This 
reduction may amount to as much as 50 to> 60 per cent, as in the case 
of spinach, or to as little as 6 to 15 per cent in the case of peas. 
In general, this shrinkage permits a closer and more attractive pack. 
If care is not exercised, however, it may lead to overfilling, as with 
mature peas and lima beans, which swell during the subsequent 
processing. 
The expulsion of air from the tissues by scalding reduces the in- 
ternal strain on tin cans during processing and permits a higher 
vacuum. 
When scalding is done in boiling water, there are losses of soluble 
food materials. These may amount to as much as 16 to 30 per cent 
of the total dry matter, as in the case of spinach, or as little as 1J 
to 10 per cent in the case of string beans. When the scalding is done 
in steam, very little of such loss takes place, unless the water of con- 
densation is allowed to drip through the material. 
Neither scalding alone, nor scalding followed by chilling in cold 
water, results in a more complete retention in the finished product of 
the natural colors of the fresh vegetables than is obtained Avhen there 
is no preliminary scalding. Since scalding helps to eliminate air 
from the material, it may reduce the amount of discoloration due to 
oxidation which takes place in canned goods. 
Scalding has very little effect on the flavor and taste of vegetables 
packed in glass jars. If the scalding is in water, the product may 
not be as sweet as that not scalded. When canned in tin, the un- 
scalded product retains more of the natural flavor than that which 
has been scalded. This may be objectionable with some vegetables, 
such as spinach, but in most cases, in the opinion of the writers, the 
unscalded product is superior in flavor, 
