SOURING OF CREAM.

New Zealand Mail, Issue 1193, 11 January 1895, Page 6

SOURING OF CREAM.

The statement is often made (writes Mr E. H. Farrington, of the Illinois, U.S.A., Experiment Station) that uniformity in tho good quality of butter from Denmark is caused not alone by cleanliness in barns and dairies, but by the addition to the cream of pure culture of a ferment which develops a fine flavourin the butter. The fermentation or souring of cream is caused by bacteria. These are plants which are seen only by the aid of a powerful microscope. They multiply amazingly fast when kept at tho proper temperature. Among plants which we can see without any microscope there are certain kinds which we call weeds. If weed seeds are in the soil they grow as well as the good seed which we plant. The same thing is true of the microscopic plants, bacteria. There are some which we are as anxious to keep out of cream as we are to prevent the growth of weeds in a cornfield, and there aro others which at present are considered to be the agents in producing a fine flavour in butter. Dirt is the source of nearly all " bad " bacteria which find their way into milk, cream, and butter. If everything through which the milk passes were clean it would be a comparatively easy matter to plant a pure culture of bacteria in cream and get that ferment alone, or in large excess over all others, but, like weed seeds in the soil, w.o have to contend with "bad" bacteria, which grow up and choke the good seed and all the superior qualities thereof. If great care were taken to keep the cows clean, the milker clean, and the milk dishes clean there would bo a greater certainty of producing a high flavoured and priced butter than where cleanliness is neglected, because there are fewer " weed seeds " in clean milk and cream.

The rate at which cream ripens in ordinary practice is not often uniform,

It is influenced not only by the clean- | liness of the milker and dairyman, as mentioned above, but the weather, the temperature at which the cream is set for ripening, and the amount of fat in the cream, all influence the rapidity of souring. Hot or warm, muggy weather has a tendency to hasten souring, while a clear, bright atmosphere, as well as cold, is not so favourable for the growth of the bacteria which cause cream to sour. Since it is the milk sugar which ferments when cream sours, it is obvious that thin cream, with only 10 to 15 per cent, fat, contains more milk sugar and will sour faster than rich cream which contains more" fat and consequently less milk sugar and casein. These uncertain quantities, cleanliness, weather, and richness of cream, which all have an on the rate at which cream sours, show the value of some simple test which would indicate the amount of acidity in cream for churning. It is a w§ll-kribwn fact that after cream has soured to a certain point another kind of fermentation takes place that injures quality of the butter. A simple test that will indicate the a mount,,of acid; in cream can be used to show when creaui is sour enough to suit the standard adopted "by different men and markets. A uniformity in the sourness can thus be obtained by churning each lot of cream when the test shows a certain amount of acidity, and no lot of cream need to spoil from overripeness, as the test will show clearly when the danger point is being approached. ' CREAM TESTING WITH ALKALINE TABLETS. In following lip this line of work the writer has developed a method of cream testing; with alkaline tablets. There are certain substances which have the property of producing a different colour in acid liquids from that which they form in an alkaline solution. They are called indicators, and have long been in use by chemists. The acidity of a liquid is generally measured by observing how much of a standard alkaline liquid, whose exact strength is known, it is necessary to add to a measured amount of the acid liquid in order to produce in it a change of

colour. The indicator, which must be added to the acid liquid to be tested, shows by the change of colour just the point when sufficient alkali has been added to neutralize the acid present in the tested liquid. The greater the unknown amount of acid in the liquid, the greater will be the amount of the known alkaline liquid used. In applying this principle to sour cream a formula has been worked out by which a definite amount of solid alkali can be made into a tablet about the size of a sixpence, containing both the alkali and indicator necessary for testing the acidity of the cream in dairy and farmhouse..

The tablets can be used for testing the sourness of the cream in the following way :-7-Label several clean, small 4oz or 6oz bottles. No. 1, No. 2, No. 3. Put one tablet in each of the bottles numbered 1, two in each numbered 2, arid three in each numbered 3. Add to each bottle enough clean water to completely cover the tablets, and let them stand until the tablets are all dissolved. When the solution is complete the bottles will contain a reddish coloured liquid, the alkaline strength of •which is indicated by the number on the label of the bottle, which shows hov? many tablets were put into each of the bottles. The cream to be tested should be thoroughly mixed. Then measure 25 cubic centimeters of the cream into a glass tumbler or small dipper. If the cream is very thick, 25 c.c. of clean water may be mixed with ifc in the dish. The sourness of this cream is ascertained by adding the reddishcoloured solution of the tablets to this measured quantity of cream until it retains a pinkish colour. The pink colour does not remain permanent until the acid of the cream is completely neutralised by the alkali of the tablets. An excess of the alkali causes the colour to increase, so that the acidity of the cream is measured by adding just enough of the alkali to produce a permanent change of colour from white to pink, and no more. No further addition of the alkali is necessary, as the first change of colour indicates the point when the acid is all neutralised. The amount of alkali required to produce this change shows the sourness of the cream as indicated by this test. A change of colour may be produced in 25 c.c. of sweet cream by a solution of

one tablet. As the sourness of the cream increases, 25 c.c. of it may require a solution pf two, three, or

four tablets to change the colour. The indications are that a cream which requires a solution of five or more tablets to change its colour is too sour. The butter from such cream will be “off flavour.” The only general direction which can now be given, as applicable to nearly all cream, is to churn it when 25 c.c. of the thoroughly mixed cream will give a pink colour with a solution of three or fore tablets, comparative trials made by each person of the acidity of the cream and the flavour of the butter made from it will be the best guide to follow.