■202 ON THE DIFFERENT METHODS OF MAKING AND 



channel between two pans inside each other, or between a false 

 and true bottom, into which cold water or broken ice can be 

 introduced. The deep cans are only suitable for such covmtries 

 as Sweden or America, where a very low temperature can be 

 reached by the application of ice, of which more anon. 



The antiquity of the separation of cream from milk might 

 indicate in this age something like 2ii'oficiency in the art. Never- 

 theless the best method is far from being settled, and the various 

 ones practised have each its advocate, hrmly asserting the 

 superiority of that particular mode. Opposite practices thus 

 increase confusion to the beginner, and this state of matters will 

 not be much altered until manipulators have a much better idea 

 of milk constituents, and the laws and circumstances which 

 affect them. A short explanation of some of the leading prin- 

 ciples may tend to establish a clearer road through the labyrinth 

 of theories, ideas, and written and itn written practice. Cream 

 rises on account of its specitic gravity, being less than the sur- 

 rounding milk, the difference, however, being so slight that a 

 very sluggish upward movement is given to the globules, — so 

 much so that some of the smaller and more dense never rise at 

 all. Sometimes even, from a difference of composition and 

 consequent opacity, large ones may not rise ; but the best 

 portion always rises first and is highest coloured. Colour, 

 flavour, and quality lose, but keeping qualities improve, with 

 each successive skimming. But undue skimming, — say after 

 48 hours at 60°, — will deteriorate the quality, so as to do more 

 tlian compensate for the small increase of quantity thus gained. 



I'ats expand and contract more than water with alterations 

 of temperature, and the greatest difference of the specific gravity 

 of milk and cream exists when hot, the least when cold. And 

 as fat — the jirincipal constituent of cream — swells more with 

 heat, and shrinks iQore with cold, than water, — the principal 

 one of milk, — it is evident that in an unvarying temperature 

 cream will rise more readily luider the influence of a high one. 

 The colder the milk the slower the rise ; because there is less 

 difference in the specific gravity of the milk and cream, and also 

 because the milk, then more dense, will obstruct it. This is 

 illustrated in tlie making of whey butter, when a temperature of 

 170° is resorted to ; because the difference of the specific gravity, 

 caused by the greater swelling of the cream than the water of 

 the whey, raises the former in a very short time. At half the 

 temperature — 85° — the difference being less, four times as long 

 is required to bring up all the cream that will rise. 



It has been observed by Professor Arnold that fat expands 

 twice as much as water with the same increase of temperature, — 

 from 60° to 130°. But in the ten degrees between 40° and 50° 

 water only expanded one-tenth of the ten between 80° and 90°; and 



