The Chemistry of Cookery

No certificate from the public analyst is demanded to establish the absence of the poison from any given sample of tapioca, as the juice of the Manihot root, like that of other spurges, is unmistakably acrid and nauseous. Sago, which is a starch obtained from the pith of the stem of the sago-palm and other plants, is prepared in grains like tapioca, with similar results. Both sago and tapioca contain a little gluten, and therefore have more food-value than arrowroot. The most familiar of our starch foods is the potato. I place it among the starch foods as next to water; starch is its prevailing constituent, as the following statement of average compositions will show: Water, 75 per cent.; starch, 18·8; nitrogenous materials, 2; sugar, 3; fat, 0·2; salts, 1. The salts vary considerably with the kind and age of the potato, from 0·8 to 1·3 in full-grown. Young potatoes contain more. In boiling potatoes, the change effected appears to be simply a breaking up or bursting of the starch granules, and a conversion of the nitrogenous gluten into a more soluble form, probably by a certain degree of hydration. As we all know, there are great differences among potatoes; some are waxy, others floury; and these, again, vary according to the manner and degree of cooking. I cannot find any published account of the chemistry of these differences, and must, therefore, endeavour to explain them in my own way. As an experiment, take two potatoes of the floury kind; boil or steam them together until they are just softened throughout, or, as we say, ‘well done.’ Now leave one of them in the saucepan or steamer, and very much over-cook it. Its floury character will have disappeared, it will have become soft and gummy. The reader can explain this by simply remembering what has already been explained concerning the formation of dextrin. It is due to the conversion of some of the starch into dextrin. My explanation of the difference between the waxy and floury potato is that the latter is so constituted that all the starch granules may