Butter and Butter Products 213some bakery and confectionery products in
which a harder fat is required. Fractionation
of milk fat to produce high - and low - melting
fractions has addressed this problem to some
extent. Unlike other processes employed by
the edible oil industry to modify the physical
properties of fats and oils, such as interesteri-
fi cation or hydrogenation, fractionation has
minimal effect on the valuable milk fat fl avor.
Fractionation of milk fat is normally
carried out by dry fractionation only, that is,
fractionation from the melt, without additives
such as solvents or detergents. The molten
AMF is slowly crystallized under controlled
conditions to the desired temperature to crys-
tallize out milk fat stearin (hard) and olein
(soft) fractions. The crystallized fraction is
harvested using special fi lters as the specifi c
temperature is reached. The fi ltrate is then
cooled to a lower temperature to crystallize
another fraction, which is harvested, and the
process continues. Fractionation of milk fat
typically starts with a milk fat with a soften-
ing point (milk fat melts over a wide tem-
perature range) of 33 ° C (91.4 ° F) and
produces a hard fraction with a softening
point around 43 ° C (109.4 ° F) and a soft frac-
tion with a softening point around 21 ° C
(69.8 ° F); a second soft fraction with a soften-
ing point below 10 ° C (50 ° F) also may be
collected (Burgess 2001 ). The melting prop-
erties of the milk fat fractions differ depend-
ing on how they are obtained, that is, cooling
rate, agitation, and number of steps employed
in the fractionation process (Kaylegian
1999 ).
The selectivity of crystallization and effi -
ciency of separation is lower in the dry crys-
tallization process than when solvent is
added. Triacylglycerols have a tendency to
form solid solutions, which greatly reduces
the effi ciency of separation; hence, crystal-
lization conditions for milk fat, with its high
content of triacylglycerols, must be carefully
managed to minimize their formation. Nucle-
ation is the fi rst step, and it occurs when the
melted milk fat becomes supercooled, i.e.,this creates an emulsion with small air
bubbles as the dispersed phase, which is dif-
fi cult to separate. After heating, the oil is held
at the temperature for a short time to allow
the proteins to aggregate before being
pumped into the concentrator. Several sepa-
rators may be operated in series to concen-
trate the butter oil and remove the separated
sedimented solids. After concentration, the
oil is heated to 90 ° C to 95 ° C (194 ° F to
203 ° F) and further dried in a vacuum dryer
before packaging.
Refi ning
AMF may be refi ned for various purposes by
polishing, neutralization, fractionation, and
plasticizing.
Polishing
Polishing produces a clear, shiny (or bright)
product. It entails the addition of water
(20% to 30%) to the oil leaving the fi nal
concentrator, a short holding period, and
then separation out of the water with
removal of water - soluble solids, mainly
protein (desludging).
Neutralization
Free fatty acids (FFA) contribute a distinctive
fl avor to dairy products but their content
must be controlled to prevent adverse fl avor
development during storage. Neutralization
of the FFA in AMF may be carried out by
mixing dilute sodium hydroxide (8% to 10%
weight/weight depending on FFA content)
into the oil. After holding for a short period,
hot water is added (20% to 30%) and the
saponifi ed FFA fraction is separated out in a
centrifugal separator along with the aqueous
phase. This process is not permitted by some
countries.
Fractionation
The physical properties of milk fat make it
unsuitable for many applications, especially