ESTIMATION OF MOISTURE IN CHEESE.

New Zealand Journal of Agriculture, Volume XL, Issue 3, 20 March 1930, Page 197

ESTIMATION OF MOISTURE IN CHEESE.

METHODS RECOMMENDED BY THE DAIRY SCIENCE ASSOCIATION.

The introduction of the manufacture of standardized cheese in New Zealand has made the chemical analysis, of cheese a question of major importance. The opportunity was therefore taken at a recent inaugural meeting of the New Zealand Dairy Science Association to discuss the various methods of analysis in.use in the dairy factories and gradingstores, with the object of finally formulating a method which could be adopted as a standard. As a result of the discussion, and partly on the basis of the figures submitted by Dr. F. H. McDowall, of the Dairy Research Institute (N.Z.), the following' procedure was drawn up and approved by the meeting. ' r ' .

SAMPLING.

The distribution of the three chief constituents of cheese viz., casein, fat, and moisture throughout a cheese, or throughout the cheeses from one vat of milk, is not uniform, due both to actual variations in the composition of the cheese as taken from the press, and also to the differences in the rate of loss of moisture by evaporation in the curing-room. It is therefore not possible to obtain a representative sample of the make of cheese from a vat by taking one plug from one of the cheeses with a trier. It was agreed that in order to avoid excessive plugging of cheese analysis should if possible be carried out on only one plug of cheese, and that the errors in sampling should be taken into account in a consideration of the analytical results. It was the opinion of the meeting that the standard position of sampling as adopted by the Dairy Division for use in the grading-stores should also be recommended for adoption in the. dairy factories— i.e., at a position on the circumference of the cheese one-third of the distance from one end. Not less than 1 in. of the cheese should be returned to the plug-hole.

Figures were quoted showing that a cheese - plug rapidly loses moisture on exposure to the open air, and it was agreed that plugs should be placed, immediately they were drawn, into a tightly corked sample tube or bottle. The tube should be kept in a cool place, away from sunlight, in order to prevent evaporation from the plug on to the side of the tube, and also running of fat. .. .

PREPARATION OF SAMPLE.' • It was unanimously agreed that a homogeneous sample could be prepared most satisfactorily from a plug of cheese by grinding rapidly to a paste in a glass or porcelain mortar, with subsequent cutting into small lumps with a knife and a spatula, and immediate transference back to the sample tube or bottle. For an accurate determination of the figure for fat in water-free solids it is essential that a homogeneous sample should be used for fat and moisture determinations after preparation of the homogeneous sample. It should be- kept in a wellcorked bottle. ■ -

A sample so prepared is somewhat difficult to introduce into an ordinary Babcock milk-testing bottle. When such bottles are being used the sample may be prepared by cutting the cheese plug into very thin strips, which are thoroughly mixed before the removal of a portion for determination of fat. The cutting should be carried out rapidly, and during the process Of cutting and filling into the bottle the cheese should be handled by means of forceps. ESTIMATION OF MOISTURE. • The moisture estimation is best carried out in wide flat dishes of nickel or aluminium. Tall dishes of the type used for butter-analysis are not so desirable, since they do not permit free circulation of air over the surface of the cheese, and a longer time is required for complete removal of moisture.

In cases where dishes of approximately equal weight are used the dish must be counterpoised exactly before each estimation. A quantity of about 5 grammes of cheese is suitable. It is considered preferable to weigh approximately 5 grammes for the analysis, and to use a table for calculation of the results from the loss in weight. Such a procedure involves admittedly two subtractions of figures as well as the noting of weights, instead of the method now in common use, where 5 grammes of cheese are weighed out and the figure of moisture content per cent, is obtained by a direct multiplication by 20 of the figure for loss in weight. The association considers that the loss in weight due to evaporation in adjusting the weight to exactly 5 grammes may often lead to inaccurate results.

It is important that the temperature and time of heating be carefully controlled. The greater portion of the moisture should be removed from the cheese at a temperature near the boiling-point of water, in order to prevent occasional loss of fat and curd through spitting. Where only one oven is available heating should be carried out at ioo° C. (212 0 F.) during hours, and the temperature should then be raised to 115 0 C. (239-240 0 F.). The heating should be continued at this temperature for 4-5 hours. It is important that the time of heating should not be either too long or too short. In the one case the loss of weight is greater than that due to evaporation of free moisture from the cheese, and if the heating is not adequate free moisture will not be completely removed. It is not difficult to obtain results which agree closely, but the results may not represent accurately the moisture - content of a cheese if the time and temperature of heating have not been carefully controlled.

An alternative method, where an electric thermostatic oven is available, permits heating of the sample overnight. The samples are heated for 15 hours at 103° C.' In this case preliminary heating at a lower temperature is not necessary, since. spitting is not liable to occur at 103° C.

After heat treatment the dishes should be allowed to cool before being weighed. The dried cheese solids take up moisture slowly from the air. Hence it is advisable to transfer the dishes from the oven to a desiccator during cooling.

In places where electric power is available the association recommends the use of the Hearson thermostatic electric oven, which permits

the accurate control of temperature. Ovens made from an electric hotplate and an oven compartment of galvanized iron are not considered suitable.

When the Hearson oven is being used to its maximum capacity the time of heating as above defined may not be sufficiently prolonged, as the dishes cover most of the holes in the oven-trays and prevent escape of water-vapour by restricting the natural circulation of air. Under such circumstances the perforated iron trays should be replaced by wire netting trays. —N.Z. Journal of Science and Technology.