Milk-and-Dairy-Products-in-Human-Nutrition-FAO

Chapter 3 – Milk and dairy product composition 65
The earliest milk products were developed to conserve the principal constituents
of milk in periods of surplus production. For example, nomadic people in Outer
Mongolia process most of the milk they obtain in the short summer season into
fermented milk, butter, and dried fermented milk products, some of which have
very long or indefinite shelf-lives and can be used in the winter when fresh milk is
sometimes unavailable (Orskov, 1995). Milk products are also easier to transport
than liquid milk, a major consideration for nomadic herders; it is common for a family
of herders in Outer Mongolia to move 6–12 times a year (Orskov, 1995). Milk
products are also a means of diversifying the diet for these people. Milk products
can also reach more distant markets: in some parts of the world, there has been a
recent increase in demand for gourmet products from various milks (Holand et al.,
2002). Products can be tailored to meet consumer demands and attract a higher price
than raw milk.
A fascinating account of the history of cheese-making is given by Fox and
McSweeney (2004). The authors report that coagulation of milk by the in situ production
of lactic acid was probably accidental, as lactic acid bacteria have the ability
to grow in milk and produce enough acid to lower the pH of milk, causing the milk
proteins to coagulate. Similarly, the use of rennets to coagulate milk may also have
initially been accidental: before the development of pottery (~5000 BC), milk was
commonly stored in bags made from the stomachs of slaughtered animals. Enzymes
(chymosin and some pepsin) in the stomach tissue would have caused the milk to
coagulate on storage. People would then have come to realize that the shelf-life of
the curds could be extended by dehydration or by adding salts.
Figure 3.3 shows the dairy commodity tree, a symbolic representation of
the flow from a primary commodity to various processed products derived
from it, together with the conversion factors from one commodity to another.
For example, the extraction rate 14 for butter from whole milk is 4.7 percent,
while it is 93 percent for butter from skimmed milk (first level processing). The
skimmed milk can be converted into a range of products (second level), including
skimmed-milk cheese (extraction rate 18 percent) and fresh whey, evaporated
skimmed milk (extraction rate 40 percent), condensed skimmed milk (extraction
rate 36 percent) and dry skimmed milk (extraction rate 10 percent). Some of
these products can be further processed to give further products (third level),
such as processed cheese from skimmed-milk cheese. When you consider that the
products formed can vary with milk source (cow, buffalo, goat etc., although not
all products are possible with all milks) and the large range of varying products
present within some of these categories (e.g. cheese), an idea of the vast number
of dairy products available is obtained. However, the majority of published
research concerns cheese and fermented milk products, with particular emphasis
on the microbiology of these products.
Table 3.7 shows the composition of some of these products, excluding cheese.
14 Extraction rate relates to processed products only and indicates, in percent terms, the amount of
the processed product concerned obtained from the processing of the parent/originating product, in
most cases a primary product.