H.—34.

(g) Starters for Butter (W. J. Wiley, G. A. Cox, and H. R. Whitehead).—Starters are not used in New Zealand with the object of " ripening " the cream, as it is well established that butter from ripened cream deteriorates in cold storage. Some factories, however, which receive sweet cream add a small proportion of starter (about 0-5 per cent.) to the pasteurized and chilled cream and hold overnight at a low temperature before churning to improve the flavour of the butter. There is no development of acidity in the cream under these conditions, although the resultant butter has a somewhat " brighter" flavour than if made from sweet cream alone. Experiments carried out during the year showed that there is an appreciable development of diacetyl in the cold cream and that it is this diacetyl which brightens the flavour of the butter. The diacetyl is produced in the cold cream by the action of Str. cremoris in the starter, and not by the betacocci, which at higher temperatures are responsible for the production of diacetyl in starters. It follows that there is no necessary relationship between the flavour and aroma of a starter grown in the usual manner at 21° C. and its ability to produce diacetyl at low temperatures. A single strain of Str. cremoris can be as effective as a good mixed butter-starter. The rate of production of diacetyl by starters at 21° C. has also been studied. Typical mixed cultures of Str. cremoris and betacocci produce diacetyl rapidly during their period of logarithmic growth rate. After reaching a peak value the proportion of diacetyl falls rapidly, and about 90 per cent, is destroyed in about twelve hours. This somewhat unexpected phenomenon has hitherto escaped the attention of workers interested in butter cultures. Examination of " ripe " starters twenty-four hours or more after inoculation gives no indication of the rapid formation followed by equally rapid destruction of diacetyl, which has occurred within the first twenty hours or so. No explanation of the phenomenon is forthcoming at present. It has been shown, however, that the betacocci are primarily responsible. Pure cultures of betacocci when grown in milk at 21° C. do not produce any appreciable quantities of diacetyl over long periods of time. When grown in milk acidified to pH 4'2, however, they produce and destroy diacetyl in a similar manner to the mixed butter cultures. (A) Land Cress Taint in Cream, and Butter (F. H. McDowall).—During the spring months of the dairying season trouble is frequently experienced in butter-factories through the presence of land cress taint in cream. The trouble is very prevalent in the east coast districts of the North Island, but each year it appears to become more widespread in other districts. The plant (Coronotus didymus) ■is an annual which germinates in open soil conditions. It is particularly in evidence, for example, in young grass, or in areas around a gate that have been trodden bare of grass during the winter. The taint is often difficult to detect in cold cream, but is accentuated by the pasteurization process. During the year under review some attention has been given to a study of the problem. Steam distillation of the plant, and extraction of the steam distillate with petroleum ether, yielded 0-02 per cent, to 003 per cent, (based on the undried material) of an essential oil with an odour strongly reminiscent of cress. The main constituent (at least 70 per cent, to 80 per cent, of the oil) has been identified as benzyl cyanide, but there are also some unidentified "constituents, one or more of which contain sulphur. While both the oil and artificial benzyl cyanide have an odour somewhat resembling land cress taint, they do not give the true land-cress taint when added to cream or butter. It was shown that the vacreator could remove a considerable portion of the cress oil or artificial benzyl cyanide added to cream. With natural cress tainted cream, however, great difficulty is experienced in effecting any improvement. Now that some idea has been gained of the nature of the tainting substances it is proposed to work with naturally tainted creams, and to study the relationship of time of consumption of cress by the cow and quantity consumed to degree of taint in the milk and cream. For this purpose arrangements have been made with the Grasslands Division of the Plant Research Bureau for the seeding of an area with land cress so that adequate material will be readily available. (i) Hardness of Butter (R. M. Dolby).—The body of butter is an important characteristic from the point of view both of its " standing up " qualities and of its spreading capacity. The estimation of body by subjective methods is unreliable even when samples are compared at accurately controlled temperatures, as the observer is frequently influenced as much by the texture as by the firmness of the butter. A method involving measurement of the properties is therefore necessary for comparing different samples of butter. An instrument designed by Dr. Scott Blair, of the National Institute for Research in Dairying at Reading, has been used to make a preliminary survey of the effect of various factors on the hardness of butter." While the method used is open to criticism on some points, notably that the readings are affected to some extent by crumbliness as well as by the hardness of the butter, it has given useful indications in this survey. It was found that the most important factor influencing the hardness of butter was the rate of cooling the cream after pasteurization. The more rapidly the cream is cooled the harder the butter. Variations in churning temperature produced much smaller differences. Variations in wash-water temperature produced very little effect, but there was a slight tendency for the hardness to be increased where warmer wash-water was used. The amount of working of the butter had surprisingly little effect on the hardness. Overworking tended to make the butter slightly softer, but the difference largely disappeared after the butter had been stored for some time. Cold storage for four or five months at 15° F. was found to produce a slight increase in the hardness of all the butters examined. A striking feature of the results was that seasonal and even daily variations were greater than variations produced by the different methods of treatment. Butter made in the early spring was very soft. The hardness increased rapidly as the season advanced, reaching a maximum about December, and declining again in the later months.

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