The literature of cheese-making contains reference to more than 500 names for varieties of cheese. Many of these can be thrown readily into great groups or families in which there are variations in unessential detail without modifying the characteristic texture and flavor of the product. Many varietal names are attached to the product of single factories or factory groups. Such varieties frequently differ only slightly in size or shape, or in stage of drainage or of ripening, from widely known varieties or other similar local forms. The descriptions recorded for such varieties commonly emphasize minor differences in manipulation without showing differences in essential factors. Vessels of particular size are prescribed to be made of wood, earthenware, or of a special metal. These details specify the exact size and shape of hoops, the use of particular styles of cutting or breaking instruments and of certain stirring tools, the material and construction of mats and draining racks.

The descriptions themselves are very commonly inadequate. The variable factors in cheese-making are fat-content of the milk, acidity, temperature of setting, amount of rennet, time allowed for curdling and the method of draining the curd. The differences in practice lie, with few exceptions, in the amount or intensity of particular factors, not differences in kind or quality of treatment. Such contrasts are quantitative, not qualitative. A great number of combinations is possible by small variations of these factors.

Varieties selected as types of groups give marked contrasts in character, but comparison of large numbers of forms shows that almost every gradation from group to group can actually be found. Within groups frequently the same physical results in texture and flavor can be obtained by combinations or adjustments of factors for the purpose of offsetting or counteracting the effects of one change in practice by the manipulation of other factors. In ripening, an equally large range of practices makes possible the development of very different qualities in mature cheeses from the same lot.

Only a few of the large number of described varieties have obtained even national importance; fewer still are known outside the country of origin. In spite of the success of special products when properly advertised, the largest place in the market is clearly accorded to the standard forms which are widely known.

104. Basis of classification.—A series of these widely known forms has been chosen as typical of groups in a system of classification adapted from the French of Pouriau. No completely satisfactory scheme of classifying all of these varieties has been devised. The grouping proposed here is based on the principles of curd-making already discussed together with consideration of the ripening processes to be discussed with each group. The factors that actually influence the quality of the final product are separated as completely as possible from non-essential operative details.

The common use of the terms "soft" and "hard" cheese is based on the single arbitrary fact of texture. The term "semi-hard" cheese may be conveniently applied to a miscellaneous group of unrelated families which are intermediate in texture between such soft forms as NeufchÂtel or Camembert and really hard cheeses like Cheddar or Parmesan. Although these terms are not made the main basis of the proposed grouping, their application to sections is indicated. Classification based on the essential facts of manufacture is, however, really helpful.

Such a classification brings together series of products in which there is essential similarity in the final output, however great the differences in manipulation. It does not consider all varieties and specialties. Some of these groups are important enough to demand special mention.

105. Processed cheeses.—Cheese of any group may be run through mixing and molding machines and repackaged in very different form from that characteristic of the variety. In such treatment, the texture and appearance may be so changed as to give the effect of a new product. Substances (such as pimiento) are added to change the flavor. Or the product may be canned and sterilized with equally great change of flavor and texture. One thus finds Club made from Cheddar; Pimiento from Cream, NeufchÂtel or Cheddar; similarly olive, nut and other combinations are made. The possible variations are numerous.

106. Whey cheeses.—Several products bearing cheese names are made from whey. These take the forms of the recovery of the albumin and casein separately or in a single product, and the recovery of the milk-sugar either alone or with the albumin. Whey cheeses have been especially developed by the Scandinavian people, although some of them have their origin in the south of Europe. Certain of these varieties are produced on a limited scale in America.

There are a number of forms fairly widely known that are difficult to place in this scheme of groups. Among these are Caciocavallo, Sap Sago.

107. Soft and hard cheeses.—Another commonly used classification makes two groups: (1) soft cheeses; (2) hard cheeses. In such a classification the semi-hard group presented here is included with the soft cheeses. Some cheeses of this group are soft in texture. This is correlated with high water-content, high fat-content or both together.

108. Relation of moisture to classes.—In this classification the water-content reflected in the texture of the cheese assumes first place. To carry the analysis somewhat further by showing the correlation between water-content and certain factors, a tabulation of well-known varieties of typical groups is presented (Table III). In this table the series of typical dairy products are first arranged according to water-content of the final product. Approximate limits of percentages of milk-fat are also given, because milk-fat frequently affects texture to a degree almost equal to water. Column 4 gives the period within which the more quickly perishable cheeses are usable, and the length of the ripening for the more solid forms. The correlation between water-content, texture and the time of keeping is clearly shown for most varieties.

TABLE III

The soft cheeses are quickly perishable products. Bacteria and molds find favorable conditions for growth in products with 45 to 75 per cent of water. If such growth is permitted, enzymic activities follow quickly with resultant changes in appearance, texture, odor and taste. Refrigeration is necessary to transport such cheeses to the consumer, if properly ripened. Trade in these forms may continue throughout the year in cool climates and in places where adequate refrigeration is available. Practically, however, outside the large cities this trade in America is at present limited to the cold months; inside the large cities much reduced quantities of these cheeses continue to be handled through the year.

In the stricter sense, the soft group of cheeses falls naturally into two series: (1) the varieties eaten fresh; and (2) the ripened soft cheeses. Those eaten fresh have a making process which commonly involves the development of a lactic acid flavor by souring, but no ripening is contemplated after the product leaves the maker's hands. In the ripened series, after the making process is completed, the essential flavors and textures are developed by the activity of micro-organisms during ripening periods varying in length but fairly well-defined for each variety.

In contrast to the soft cheeses, the hard kinds are low in water-content, ripen more slowly and may be kept through much longer periods. They retain their form through a wider range of climatic conditions. They develop flavor slowly and correspondingly deteriorate much more slowly. Such cheeses are in marketable condition over longer periods. In their manufacture the cooking of the curd takes a prominent place.

109. Relation of heat to classes.—The close relation between the heat applied and the product sought forms the basis of a striking series of graphs (Fig. 12, page 78). These show the changes hour by hour in the heat relation during the making process of a series of widely known forms, each of which is chosen as typical. In some of these forms, heat is applied but once to bring the milk to the renneting temperature typical for the variety. Subsequent manipulations are accompanied by a steady fall in temperature. In other forms, the curd when solid is specially heated or "cooked" to bring about the changes characteristic of the variety. These contrasts are clearly brought out by the graphs which represent practices well recognized for the varieties. The detailed process for these groups is considered in succeeding chapters.