organism can no longer grow. With other proteases from the rennet, they
release free amino acids (principally glutamic acid and leucine in Ched-
dar) and peptides which contribute to the cheese flavour. In some cases
this can give rise to a flavour defect: casein proteins contain a high
proportion of hydrophobic amino acid residues such as leucine, proline
and phenylalanine and if they are degraded to produce peptides rich in
hydrophobic residues, the cheese will have a bitter taste.
The lipolytic and proteolytic activities of moulds play an important
role in the maturation of some cheeses. In blue cheeses such as Stilton,
Penicillium roquefortii grows throughout the cheese. It can grow at
reduced oxygen tensions, but aeration is improved by not pressing the
curds and by piercing the blocks of curd with needles.P. camembertiiis
associated with surface-ripened soft cheeses such as Camembert and Brie.
The keeping qualities of cheese vary with the type but are always much
superior to those of milk. This is principally the result of the reduced pH
(around 5.0 in Cheddar), the low water activity produced by whey
removal and the dissolution of salt in the remaining moisture. Under
these conditions yeasts and moulds are the main organisms of concern.
The latter are effectively controlled by traditional procedures to exclude
air such as waxing or by modern refinements such as vacuum packing.
9.7 Fermented Vegetables
9.7.1 Sauerkraut and Kimchi
Most horticultural products can be preserved by a lactic acid fermenta-
tion. In the West the most important commercially are cabbage, cucum-
bers and olives, although smaller amounts of others such as carrots,
cauliflower, celery, okra, onions, sweet and hot peppers, and green
tomatoes are also fermented. In Korea fermented vegetables known as
kimchi are an almost ubiquitous accompaniment to meals. More than 65
different types of kimchi have been identified on the basis of differences in
raw materials and processing. Cabbages and radishes are the main
substrates but garlic, peppers, onions and ginger are often also used.
Surveys have shown its importance in the Korean diet, variously reporting
kimchi to comprise 12.5% of the total daily food intake or a daily adult
consumption of 50–100g in summer increasing to 150–200 g in winter.
Sauerkraut production is thought to have been brought to Europe
from China by the Tartars. Like a number of other traditional fermen-
tations, the commercial process is technologically simple (Figure 9.9),
but involves some interesting and complex chemistry and microbiology.
Usually where sauerkraut is produced commercially special cabbage
cultivars are grown. These tend to have a higher solids content than
normal and so minimize production of liquid waste during processing.
336 Fermented and Microbial Foods