Be this as it may, we must free our minds from all suppositions which might qualify the exactness of the principles upon which our new process is founded, or cause any doubt in the minds of our readers as to the possibility of its application and the benefits to be derived from its adoption. § I.—On the Conditions which cause Variations in the Nature of the Organized Products existing in Infusions. We have proved by experiment, in the preceding chapter, that a few minutes’ boiling renders liquids, and more especially wort, absolutely free from liability to change when in contact with pure air, that is, air which contains none of the germs of organisms that are continually floating about in the atmosphere. What is true in the case of wort is equally so in the case of all organic liquids; there is not a single one that could not be rendered inaccessible to any subsequent change if it were brought, first of all, to a suitable temperature, which would vary with the nature of the liquids. Amongst them there are some which, like vinegar, lose their tendency to change after having been rapidly raised to a temperature of not more than 50° C. (122° F.); others, like wine, require a greater heat. Wort, to which no hops have been added, should be subjected to a temperature of not more than 90° C. (194° F.); milk to about 110° C. (230° F.).[21] It is easy to show that these differences in temperature, which are required to secure organic liquids from ultimate change, depend exclusively upon the state of the liquids, their nature, and, above all, on the conditions that affect their neutrality, whether towards acidity or alkalinity; for it is not difficult to observe that the least changes in these respects lead to considerable variations in the temperatures which we must employ.[22] We could adduce many examples of this. The only difference between the nature of must and that of wine is caused by fermentation. We may say the same thing of wort and beer, and, better still, of new milk and sour milk. Must, to be secured from change, requires a much higher temperature than wine does; similarly, wort requires a much higher temperature than beer. Milk must be heated to about 110° C. (230° F.), as we have just stated, but sour milk would require 20° C. or 30° C. (36° F. or 54° F.) less. Wine, when fresh, ceases to be liable to change after it has been brought to a temperature below 100° C. (212° F.); it requires a temperature of more than 100° C. in the presence of carbonate of lime.