Between 3% and 6% of the rennet added to the cheese milk is retained in the
curd. This is influenced by the pH at whey drainage; with increasing pH, a smaller
amount of rennet is retained in the curd. Very little coagulant survives the high cooking
temperatures used for Swiss-type cheeses. In the initial stages of maturation,
αs1-casein is degraded by rennet. The amount of intact αs1-casein is related to the
firmness of the cheese. If the level of primary proteolysis is excessive, off-flavors due
to bitter peptides can occur. β-Casein and αs1-casein are both hydrolyzed by rennet
in vitro. In Cheddar and Dutch-type cheeses, only αs1-casein is completely degraded.
In the cheese environment, the β-casein peptides liberated are different from the
rennet specificity, suggesting that plasmin and bacterial proteinases are responsible
for the hydrolysis.1