THEORY OF CHURNING. 305 



out, of salt butter is always clear and transparent, while the 

 liquid squeezed out of fresh butter is usually milky. 



By warming to a temperature near the melting point of the 

 fat considerable quantities of water can be mixed with butter. 

 In the preparation of " pickled " butter advantage is taken of 

 this fact to add large amounts of salt by working in warm brine. 

 Butter treated in this way does not lose its water easily, as an 

 emulsion of fat and water is thus produced. 



Storch has shown that by the action of certain micro-organisms 

 such a condition (of the proteins ?) is produced, that large amounts 

 of water are retained and cannot be worked out. In this case 

 an emulsion is produced, which contains large numbers of veiy 

 minute water globules. These butters are designated " thick," 

 and are rare in England. 



Theory of Churning. — Several theories have been put forward 

 to account for the phenomenon of churning. Thus, Fleisch- 

 mann holds the view that the globules of fat in milk are in a 

 superfused condition, and that churning is simply the phenom- 

 enon of solidification ; with the recognition of the fact that the 

 globules are solid at low temperatures this view is untenable. 

 Soxhlet holds that churning consists in the rupture of a solid 

 membrane, which he believes exists round the fat globules ; as 

 the existence of such a membrane is disproved, this view cannot 

 be accepted. Storch attributes churning to the gradual rubbing 

 off of a semi-solid membrane of " mucoid substance," and this 

 hypothesis has much to recommend it ; the whole of the evidence 

 points to the existence of a layer, which is not solid, round the 

 fat globules. As previously stated, the author cannot reconcile 

 Storch's theory that this layer consists of " mucoid substance " 

 with known facts ; but it appears very highly probable that there 

 is a layer, the composition of which is for the present purpose 

 immaterial, round each fat globule. As it is improbable that 

 this layer is elastic, the effect of the impact of one fat globule 

 on another will be to squeeze out the layers between them, and 

 bring the globules within the sphere of each other's attraction. 

 In this way nuclei will be formed, which will, on continued 

 churning, increase in size ; as the nuclei get larger and larger, 

 the resistance, owing to fluid friction on their surfaces, wUl 

 gi'adually bear a smaller and smaller proportion to the force 

 tending to bring them to the surface, and, at a given moment, 

 the butter will "" come." This theory is in accord with all the 

 known facts. By microscopical examination of cream during 

 churning the formation of nuclei of irregularly shaped masses 

 of fat globules is noticed. As an irregular mass will occupy a 

 greater apparent volume than a sphere, the transformation of 

 spherical globules into irregular nuclei should be attended with 



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