By methods similar to those just given the cause of the common and costly cheese fault known as “sweet flavor” has probably been found. This investigation was demanded by the occurrence in some of the best-conducted factories of outbreaks of the trouble which most thorough cleansing and scalding fail to overcome. It is believed that these attacks result in annual loss to the State of at least $10,000. The trouble is of obscure origin and is peculiar in its development, manifesting itself in flavors of varying intensity and character, from a faint sweetness to a well-marked fruity smell and taste, and seeming to appear and disappear without rule or method. This made study more difficult than in the case of well-defined troubles; but its manner of development in the cheese indicated some living germ as the cause; so the attempt at solution of the problem was made from that standpoint.
By cultural methods, study was made of the flora of good and poor cheeses; that is, the various forms of plant life existing in these cheeses were separated from each other and their forms, actions and effects noted. These forms of life were mostly bacteria and yeasts; and, contrary to the usual rule, it was the latter which finally seemed to demand attention.
Yeasts are plants a little higher in the scale of life than bacteria, a little larger but still microscopic, and differing from bacteria in their mode of reproduction, which is by budding of a new cell from an old one rather than by division of an old cell into two new ones of equal size. Their most characteristic action is the formation of alcohol and carbon dioxide; which makes them indispensable in brewing and bread making.
In good cheeses almost no yeasts were found, but in the sweet-flavored cheeses sometimes half of the germs present were yeasts; and they were always found where the sweet flavor was noticed. Yeasts have not been recognized, hitherto, as a cause for such cheese faults; but their presence in such numbers cast strong suspicion upon them; which actual work proved to be well founded, for pronounced cases of sweet flavor developed in cheeses made from pure milk inoculated with the yeasts; and the vat in which the cheese was made became contaminated so that, without further intentional inoculation, sweet-flavored cheese was produced where none had been known before. As yeasts have hitherto played minor parts in dairy investigations, no classification of those found has yet been made, nor has the exact flavor due to each one been determined. Further study is being given to the subject.
Rusty Spot in Cheddar Cheese.
Not a flavor.
Rusty spot is not a flavor trouble, as spotted cheeses of this kind may be all right in taste and smell. The spots, however, are offensive to the eye and render the cheese salable only at a reduction in price, if at all. From the Station investigations, continued for nearly two years, along much the same lines as the flavor studies but with a little more definite guide in color than in taste and smell, some direct knowledge has been gained, though not as definite as could be desired along preventive and remedial lines.
Cause and
conditions.
The rusty spots are colonies of minute plants, bacteria, growing on the walls of the air spaces within the cheese. The trouble usually appears in May, often does little harm during the middle of the summer and generally disappears in October. In cheese made with a high acid content the moisture content of the air spaces within the cheese is low, and without abundance of moisture the germs make little growth; hence the spots are too small to be noticed. The marked influence, on the germs of rusty spot, of this slight variation in the character of the cheese probably accounts for the unexpected appearance and disappearance of the spots from cheeses of an occasional day’s make in infected factories.
Cure.