454 Part IV: Milk
be consumed directly as a beverage or used for the
manufacture of a wide range of products. Gravity
creaming and butter manufacture have been used
since prehistoric times, but gravity creaming has
been largely replaced by centrifugal separation of the
fat since the development of the cream separator by
Gustav de Laval in 1878. Gravity separation is still
used to prepare reduced-fat milk for the manufacture
of Parmegiano-Reggiano cheese. The physics of fat
separation by gravity or centrifugal separation and
the process of demulsifying milk fat to butter or but-
ter oil will be described briefly later in this chapter.
Creaming (fat separation) is undesirable in many
dairy products (e.g., liquid/beverage milk, concen-
trated milks) and is prevented by a process known as
homogenization (the commonly used valve homog-
enizer was developed by Auguste Gaulin in 1905).
Homogenization prevents creaming by reducing the
size of the fat globules and preventing their agglom-
eration (clustering) by denaturing a particular minor
protein, cryoglobulin (type M immunoglobulin).
The casein micelles are physicochemically stable
but can be destabilized by a number of processes/
treatments, which are exploited for the production of
new dairy products. The most important of these are
limited proteolysis and acidification, which are used
in the production of cheese, fermented milks, and
functional milk proteins. The mechanism and conse-
quences of proteolysis and acidification will be de-
scribed briefly. Thus, the three main phases of milk,
that is, fat, casein, and the aqueous solution (whey)
can be separated easily.
Milk is remarkably heat stable and can be steril-
ized by heat in standard or concentrated form, or
dried to produce a wide range of dairy products. The
principal processes and the resulting product fami-
lies are summarized in Table 20.1. All these families
of dairy products contain many products, for exam-
ple, it is reported that about 1400 varieties of cheese
are produced worldwide.
In addition to the above considerations, milk is a
rich medium for the growth of a wide range of micro-
organisms. While this is exploited in the production
of a range of fermented dairy products, it also means
that milk can harbor microorganisms that may cause
spoilage of products, or may present health risks to
the consumer. Largely for the latter reason, very little
milk is now consumed in the raw state, the vast
majority being heat treated sufficiently severely to
kill all pathogenic and food-poisoning bacteria.
In this chapter, several of the main processes used
in the modern dairy industry will be discussed, and
the relationships between the biochemical properties
of milk and the processes applied explored.THERMAL PROCESSING OF
MILKINTRODUCTIONThe most common process applied to most food
products is probably heat treatment, which is princi-
pally used to inactivate microorganisms (e.g., bac-
teria, yeasts, molds, and viruses) associated with
foodborne disease, food poisoning, or spoilage. Sec-
ondary objectives of heat treating food include inac-
tivation of enzymes in the tissue or fluid which
would otherwise negatively influence product qual-
ity, and effecting changes in the structure of the
food, e.g., through denaturation of proteins or gela-
tinization of starch.
A wide range of thermal processes is commonly
applied to milk today, as summarized in Table 20.2.
The most widely used thermal process for milk is
pasteurization. In 1864–1866, Louis Pasteur, the
famous French scientist, discovered that the spoil-
age of wine and beer could be prevented by heating
the product to around 60°C for several minutes; this
process is now referred to as pasteurization. The his-
torical development of the thermal processing of
milk was reviewed by Westhoff (1978).
Although pasteurization was introduced to im-
prove the stability and quality of food, it soon be-
came apparent that it offered consumers protection
against hazards associated with the consumption of
raw milk (particularly the risk of transmission of
tuberculosis from infected cows to humans); devel-
opments in the technology and widespread imple-
mentation occurred early in the 20th century. The
first commercial pasteurizers, in which milk was
heated at 74–77°C for an unspecified time period,
were made by Albert Fesca in Germany in 1882
(Westhoff 1978). The first commercially operated
milk pasteurizer (made in Germany) was installed in
Bloomville, New York, in 1893 (Holsinger et al.
1997); the first law requiring pasteurization of liquid
(beverage) milk was passed by the authorities in the
city of Chicago in 1908.
Many early pasteurization processes used condi-
tions not very different from those proposed by