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9. _____, the butter must be worked vigorously to ensure even distribution of the salt. The working of the butter also influences
the characteristics by which the product is judged – aroma, taste, keeping quality, appearance and color. Working is required to obtain
a homogenous blend of butter granules, water and salt. During working, fat moves from globular to free fat. Water droplets decrease
in size during working and should not be visible in properly worked butter. Overworked butter will be too brittle or greasy depending
on whether the fat is hard or soft. Some water may be added to standardize the moisture content. Precise control of composition is
essential for maximum yield. The finished butter is discharged into the packaging unit, and from there to cold storage.
E x e r c i s e T w o
. Mark whether the statements below are true or false:
1. Milk fat is comprised only of triglycerides.
2. The triglycerides (98 % of milk fat) are of diverse composition with respect to their component fatty acids.
3. The globule membrane is comprised of surface active materials: phospholipids, glycolipids, and lipo-proteins.
4. Many milk products hardly ever foam.
5. Fats tend to spread over the air-water interface and destabilize the foam.
6. Disruption of the fat globule by interaction between the fat globule and air bubbles is frequent.
7. Milk fat is essential for the formation of stable whipped products.
8. When cream is beaten air cells form more slowly partly because of lower viscosity.
9. Churning does not occur at hot temperature.
10. If beating continues the fat clumps increase in size.
The background science of butter churning
The fat globule
Milk fat is comprised mostly of triglycerides, with small amounts of mono- and diglycerides, phospholipids, glycolipids, and
lipo-proteins. The triglycerides (98 % of milk fat) are of diverse composition with respect to their component fatty acids;
approximately 40 % of which are unsaturated fat firmness varies with chain length, degree of instauration, and position of the fatty
acids on the glycerol. Fat globules vary from 0.1 – 10 micron in diameter. The globule membrane is comprised of surface active
materials: phospholipids and lipoproteins, Fat globules typically aggregate in three ways: flocculation, coalescence, partial
coalescence.
Whipping and Churning
Many milk products foam easily. Skim milk foams copiously with the amount of foam being very dependent on the amount of
residual fat – fat depresses foaming. The foaming agents are proteins, the amount of proteins in the foam are proportional to their
contents in milk. Foaming is decreased in heat treated milk, possibly because denaturated proteins produce a more brittle protein layer
at the interface. Fats tend to spread over the air-water interface and destabilize the foam; very small amounts of fats (including
phospholipids) can destabilize a foam.
During the interaction of fat globules with air bubbles the globule may also be disrupted (this is the only way that fat globules
can be disrupted without considerable energy input). Disruption of the fat globule by interaction between the fat globule and air
bubbles is rare except in the case of newly formed air bubbles where the air-water interfacial layer is still thin. If part of the fat
globule is solid, churning will result, hence the term "flotation churning" – from repeated rupturing of air bubbles and resulting
coalescence of the adsorbed fat.
In spite of the above comments on the destabihzation of foams by fat, milk fat is essential for the formation of stable whipped
products which depend on the interaction between fat globules, air bubbles and plasma components (esp. proteins).
When cream is beaten air cells form more slowly partly because of higher viscosity and partly because the presence of fat causes
immediate collapse of most of the larger bubbles. If most of the fat is liquid (high temperature) the fat globule membrane is not
readily punctured and churning does not occur at cold temperature where solid fat is present, churning (clumping) of the fat globule
takes place. Clumps of globules begin to associate with air bubbles so that a network of air bubbles and fat clumps and globules form
entrapping all the liquid and producing a stable
foam.
If beating continues the fat clumps increase in size until they become too large and too few to enclose the air cells, hence air
bubbles coalesce, the foam begins to "leak" and ultimately butter and butter milk remain.
E x e r c i s e T h r e e
. Choose the best phrase from the given below to fill each of the gaps:
So by modifying the cooling program
;
The more violent the cooling process
;
heat treatment
;
Before churning
;
low-melting fatty
acids
;
the other hand
;
In the former case
;
to their surface by adsorption
;
If cooling is rapid
;
A soft milk fat
;
is always subjected
;
The
consistency of butter
.
Crystallizing of the milk fat during aging
1. _____, cream is subjected to a program of cooling designed to control the fat so that the resultant butter has right consistency.
2. _____ is one of its most important quality-related characteristics, both directly and indirectly, since it affects the other
characteristics – chiefly taste and aroma. Consistency is a complicated concept and involves properties such as hardness, viscosity,
plasticity and spreading ability. The relative amounts of fatty acids with high melting point determine whether the fat will be hard or
soft. Soft fat has some content of 3. _____ and at room temperature this fat has a large continuous fat phase with a low solid phase,
i.e. crystallized high-melting fat. 4. _____, in a hard fat, the solid phase of high-melting fat is much larger than the continuous fat
phase of low-melting fat is much larger than the continuous fat phase of low-melting fatty acids.
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