Handbook of Food Science and Technology 3

Figure 1.26
.
 Change in constituents during ripening 
1.3.4.5.
 Errors and defects 
Given the diversity and complexity of cheese processing, manufacturers 
must face the risk of errors resulting in defects in the final product. These 
defects can be classified into two categories: coagulation and draining defects 
and ripening defects.
Coagulation and drainage defects 
The growth of lactic acid bacteria plays a key role in cheese technology. 
The bacteria act as an acidifying agent, and therefore contribute to 
coagulation, drainage and the adjustment of the degree of mineralization in the 
cheese. 
The ability of milk to allow the growth of lactic acid bacteria varies with 
the origin of the milk and the bacterial species. Milk contains a number of 

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From Milk to Dairy Products 57 
natural inhibitors (immunoglobulins, lactoperoxidase, lysozyme, lactoferrin, 
nisin, free fatty acids, leukocytes, etc.) and stimulants such as growth factors 
(group B vitamins, amino acids, nitrogenous bases, small peptides, proteose 
peptones). Subjecting milk to heat treatment may destroy natural inhibitors 
and growth factors, but it can also generate growth factors such as peptides, 
amino acids, formic acid and so on. Other exogenous factors such as 
bacteriophages, antibiotics or chemical residues can inhibit the growth of 
lactic acid bacteria.
Finally, coagulation defects (longer rennet clotting time, slower firming 
rate, formation of a soft gel with reduced cheese yield) may occur in milk due 
to its physicochemical and bacteriological composition (mastitis milk, milk 
from the beginning or end of lactation) or the type of treatment it has 
undergone (refrigeration, heat treatment, etc.).
Ripening defects 
Ripening defects can be classified into three categories: 
– 
texture and swelling defects:
these defaults can be caused by processing 
(dry, oily or runny
 
rind, split in the body of the cheese, untypical number, size 
and uniformity distribution of eye in certain semi-hard cheese
,
etc.) or 
microbiological reasons (early or late blowing, off-odor); 
– 
appearance defects (crust texture, undesirable mould growth)
: these can 
be caused by fungus on the cheese surface (“blue”, “cat hair” or “toad skin” 
defects), or fungus and bacteria on the surface and inside the cheese (cheese 
rind rot, mottled appearance with flecks of orange, cream, pink, brown, white, 
red, etc.); 
– 
flavor and aroma defects
. These include: 
- 
bitter flavor
, frequently encountered in pressed, blue and soft cheeses. 
Caseins (mainly hydrophobic 
β
-casein) are responsible for the formation of 
bitter peptides by the action of residual rennet, plasmin, penicillii, 
psychrotrophic bacteria and some starter cultures that acidify the curd rapidly, 
- 
rancid flavor
, which occurs with excessive lipolysis during ripening 
causing a large amount of short and medium chain-free fatty acids to form. 
The agents responsible are certain penicillii
,
psychrotrophic bacteria, natural 
or microbial lipases (contamination, heat-resistant enzymes, starter cultures, 
etc.), 

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58 Handbook of Food Science and Technology 3 
- 
other flavor defects
including cruciferous vegetable, mushroom, potato, 
or malt odors among others. The origins and mechanisms of their formation 
are diverse and difficult to establish. 
In conclusion, the preparation of milk is an important step because it plays 
a key role in the production of cheese. With the increase in scientific 
knowledge over the past 30 years, the various stages of processing milk into 
cheese have become better controlled: the biological, biochemical, chemical, 
and physical properties of products are constantly changing, demonstrating a 
vast variety and complexity of reactions, in particular during ripening. 
However, greater understanding of the physicochemical and microbiological 
mechanisms involved in the various stages of cheese production is needed.