THE HARD CHEESES 207 
may be only sufficient to make the cheese a little “off” in flavor 
but still passable, or-it may be so great as utterly to ruin the 
cheese and make it a total loss. Some of these faults have been 
traced to their sources and will be considered under the following 
heads: 
Swelled Cheese-—This is, perhaps, the most common fault. 
It is due to the development of a considerable quantity of gas 
which fills the curd full of holes and causes it to swell and lose 
its shape. Sometimes the holes are extremely numerous and 
small, and sometimes they are fewer but of larger 
size. In any case they are undesirable. Even 4 fre : 
good cheeses are apt to show some gas holes, °Y0 2 
but so few as to do no special injury. Some- 0 aS 
times the gas is so abundant as to cause the 
cheese to burst, in which case it is completely partite 4 using 
ruined. Between these extremes are all kinds of B. Sha fw 
intermediate grades. The development of the 
gasis accompanied by an unusual fermentation and an unpleasant 
taste and smell. The cause of the trouble is the development of 
gas-producing bacteria. Several different species are known 
which have this power of developing gas in great quantities in 
the ripening cheese (Fig. 42). Most of them, perhaps all, belong 
to the type which has been referred to in Chapter XI as Bact. 
aerogenes type. As pointed out in that chapter, the different 
varieties of this type vary much in the amount of gas they pro- 
duce; sometimes the quantity is very slight, sometimes it is 
extraordinarily large; and it is easy to understand how different 
strains and different quantities of bacteria will produce grades 
of gasiness in cheeses. 
Bitter Cheese-—The development of a bitter taste is one of 
the common troubles of cheese-makers. Sometimes this defect 
will involve the whole output of a cheese factory and cause 
heavy losses for a considerable period. Two different causes 
have been determined upon as responsible for the trouble. In 
ona 
C 
