506 FOOD PRESERVATION 
and histological studies made on poultry stored between temperatures 
of —9 and —13° C. below freezing. These birds were frozen hard. 
There was no loss in nutritive value but a change in flavor was detected 
after nine months. Chemical changes which were observed were 
thought to be due to enzymic rather than bacterial causes. The aerobic 
bacteria decreased in the muscle during storage as the period lengthened. 
Above freezing, different lots were stored at 29.3° C. at from 7.2 to 
12.8° C. and at 0° C. Bacteria in muscles and skin increased at all 
three temperatures but the increase was smaller as the temperature 
approached 0° C. The amino and basic nitrogen increased at the 
expense of protein nitrogen. 
Pressure. Hite, Giddings and Weakley (1914) studied the effect 
of pressure on bacteria in canned fruits and vegetables. The bacteria 
which caused spoilage of sweet, ripe fruits could be destroyed by pres- 
sure. One hundred thousand pounds for ten minutes stopped the fer- 
mentation of grape juice. Apple juice which was subjected to 60,000 
to 80,000 lbs. for thirty minutes remained sweet. These authors kept 
apple juice which had been subjected to 90,000 to 120,000 lbs. for five 
years. Inconsistent results, however, were secured with blackberries 
and raspberries. Tomatoes also gave such results. The work indi- 
cates that more study is necessary to overcome some of the difficulties 
of the process in its application to food preservation. Bridgman (1914) 
found that egg white became somewhat stiffened when it was exposed 
to 75,000 lbs. per square inch for thirty minutes at 20° C. Larson, 
Hartzell and Diehl (1918) found that a direct pressure of 6000 atmos- 
pheres would kill non-spore forming bacteria when applied for fourteen 
hours. It required 12,000 atmospheres for the same length of time to 
kill the spore formers. This has much significance in the sterilization 
of foods by this method since the spore formers cause much of the trouble 
in spoilage. In an atmosphere of COz2 50 atmospheres for 1.5 hours 
killed non-spore formers. 
Canning. Appert in 1802 first showed that foods could be pre- 
served if they were sterilized and kept in hermetically tight containers. 
This discovery stimulated the use of the process and it spread rapidly 
to various parts of the world. Bitting (1917) has shown the extent of 
the canning industry. For the year 1914, 103,765,923 cases of canned 
food products were put up. These were valued at $258,798,036. He 
states that the United States is not only the largest producer but also 
the largest consumer of canned foods. The future of this industry 
seems very bright and each day sees a new type of food preserved by 
this method. 
