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Theories of Churning

Theories of Churning
Course

food science (fcn123)

52 Documents
Students shared 52 documents in this course
Academic year: 2020/2021
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Sam Higginbottom University of Agriculture, Technology and Sciences

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Theories of Churning

What is churning?

Churning refers to the process of agitation of cream at a suitable temperature until the fat

globules adhere with each other forming larger and larger mass and leading to almost

complete separation of fat and serum

Theories of churning butter

There are three main theories on the churning of cream into butter:

1. Fisher and Hooker’s Phase-Reversal Theory (1917):

According to this theory, churning is a process of phase reversal, i., changing an oil-in- water type emulsion (such as cream) to a water- in-oil type emulsion (such as butter). Agitation of cream in the churning process causes coalescence and clumping of fat globules until eventually the ratio of the surface area to the volume of fat units becomes so small that it can no longer contain all the buttermilk in stable form. The fat-in-water emulsion then suddenly breaks, yielding butter grains (consisting of an emulsion of water-in-butter- fat) and free buttermilk.

Drawback:

Butter is not a true water-in-fat emulsion. Microscopic studies reveal that a proportion of fat globules in butter are still intact in the worked butter.

2. Rahn’s Foam Theory :

According to this theory, the presence of foam/froth is essential for churning. It also postulates that there is a ‘foam-producing’ substance present in cream (and milk) which gradually solidifies as the cream or milk is agitated.

Foam is created during the churning period. The fat globules, due to surface tension effects, tend to concentrate and clump on the foam bubbles. The foam-producing substance assumes a solid character and the foam collapses. The fat globules then coalesce and butter is formed.

Drawback:

Foam formation (i., the presence of air) is not required in some continuous butter-making processes.

3. King’s Modern Theory:

According to this theory, the true explanation of what takes place during churning appears to lie midway between the first two theories.

The modern conception of the mechanism of the churning process may be summarized as follows:

(i) In cooled cream at churning temperature, the fat is present as clusters (clumps) of fat globules; and within each globule it is present partly in solid and partly in liquid form.

(ii) Churning breaks up the clusters and causes foam/froth formation. The globules become concentrated to some extent in the film around the air bubbles in the foam and are thus brought into close contact with each other.

(iii) The movement of the globules over one another in the foam film and the direct concussion between them causes a gradual wearing away of the emulsion-protecting surface layer of the phospholipid-protein complex.

The globules then adhere together to form larger and larger particles. Eventually these particles become visible as butter grains (granules). As the granules form, they enclose some of the air from the foam. The fat in the granules is still mainly in globular form.

(iv) The working of butter grains causes the globules to move over one another. Under the effect of friction and pressure, some of them yield up a portion of the liquid fat. Others are broken up during working. Finally there is enough free liquid fat present to enclose all the water droplets, air bubbles and intact fat globules.

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Theories of Churning

Course: food science (fcn123)

52 Documents
Students shared 52 documents in this course

University: Sam Higginbottom University of Agriculture, Technology and Sciences

Was this document helpful?
Theories of Churning
What is churning?
Churning refers to the process of agitation of cream at a suitable temperature until the fat
globules adhere with each other forming larger and larger mass and leading to almost
complete separation of fat and serum
Theories of churning butter
There are three main theories on the churning of cream into butter:
1. Fisher and Hooker’s Phase-Reversal Theory (1917):
According to this theory, churning is a process of phase reversal, i.e., changing an oil-in-
water type emulsion (such as cream) to a water- in-oil type emulsion (such as butter).
Agitation of cream in the churning process causes coalescence and clumping of fat globules
until eventually the ratio of the surface area to the volume of fat units becomes so small that
it can no longer contain all the buttermilk in stable form. The fat-in-water emulsion then
suddenly breaks, yielding butter grains (consisting of an emulsion of water-in-butter- fat) and
free buttermilk.
Drawback:
Butter is not a true water-in-fat emulsion. Microscopic studies reveal that a proportion of fat
globules in butter are still intact in the worked butter.
2. Rahn’s Foam Theory :
According to this theory, the presence of foam/froth is essential for churning. It also
postulates that there is a ‘foam-producing’ substance present in cream (and milk) which
gradually solidifies as the cream or milk is agitated.
Foam is created during the churning period. The fat globules, due to surface tension effects,
tend to concentrate and clump on the foam bubbles. The foam-producing substance
assumes a solid character and the foam collapses. The fat globules then coalesce and butter
is formed.
Drawback:

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