A study of the types of bacteria surviving a long-term period of storage
Date
1938
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Abstract
The chief reason for storing butter in cold storage is to ensure a supply of good butter throughout the year. Most butter goes into storage in May, June and July, the season of the year which is best suited to cream production because of the freshening of the majority of the cows at this time, also the succulent condition of the pasture. Under normal conditions the bulk of butter in storage is taken out within nine months. Only in exceptional cases is butter held in storage over one year, and when this is done it is usually accompanied by a great sacrifice in quality and price.
In order to justify storage and to have the storing of butter fulfill the purpose for which it is intended, the butter must be protected against agents and conditions which cause it to deteriorate in quality. By deterioration in butter is meant any change in flavour that will tend to make it less valuable. The chief conditions injurious to the quality of butter in storage are air, light, heat and humidity.
Air and Light: It is a well known fact that prolonged exposure to air damages the flavour of butter and the changes brought about are believed to be due chiefly to oxidation. This oxidizing action is intensified in the presence of light. This fact can easily be proven by placing a sample of butter in direct sunlight and it will be found to rapidly acquire an oxidized or tallowy flavour and appearance. The tendency in storage is usually toward a tallowy character which begins on the surface and progresses toward the centre of the package.
Heat intensifies every type of butter deterioration. It hastens oxidation and the action of bacteria and enzymes; it also favours mold development, and chemical activity. Butter that is intended for prolonged storage should be stored at a temperature of zero degrees Fahr, or lower. At higher temperatures its keeping quality is jeopardized and the poorer the quality the more rapid will be the deterioration with age. It not only assists in flavour deterioration, but the mold spots must be removed which means a lot of labour and loss of butter in the scraps. In commercial cold storages the air is dry, but when butter is removed from such a storage moisture frequently condenses on the surface. When such butter is held for a few days at temperature above freezing, mold may develop and cause serious loss. Thus storage at temperatures above freezing should always be in a dry atmosphere if possible.
Storage does not improve the quality of butter, rather the flavour tends to deteriorate with age. The deterioration is usually retarded and only very gradual at the low temperatures of commercial cold storage.
The exact changes responsible for the development of specific flavour defects have not been determined in the great majority of cases. It is assumed with reasonable certainty, however, that rancidity and tallowiness are due to the cleavage of the butterfat, rancidity to hydrolysis through bacterial or enzymatic action, or both, and tallowiness to oxidation through chemical means. Butterfat, on account of its relatively high percentage of the lower fatty acids, especially butyric, readily produces a strong odour characteristic of these acids upon slight hydrolysis. Most other fats contain relatively small amounts of the lower fatty acids and a larger amount of the higher acids, such as palmitic and stearic which are less susceptible to hydrolysis. Fishiness in butter was first thought to be due to bacterial decomposition but now is supposed to be the result of the hydrolysis of lecethin, forming trimethylamine.
The work done for this thesis was to find out what types of bacteria had survived for six years, rather than to determine any specific defect that they might have caused. The sample of butter worked with had been kept in commercial cold storage for a period of six years and it was found that it had developed a tallowy appearance during this time.
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Unspecified
Department
Dairy Science
Program
Dairy Science