A FTER explaining the important part played by starch in plant life Uncle Paul took occasion to name some of the less familiar sources of this substance and to describe how it is used for purposes very different from that so well known to every housewife and every laundry-maid.
"All starch," said he, "whether it be derived from one plant or another, from a seed or from a root, is readily convertible into sugar either by the natural processes going on in vegetation or by artificial processes employed by man. The simplest expedient is the application of heat, a factor entering into the preparation of farinaceous foods. Let me illustrate by a few examples.
"A potato in its raw state is uneatable. Cooked in boiling water or roasted in the ashes it is excellent. What then has happened to it? Heat has turned a part of the starch into sugar, and the tuber has become a mass of farinaceous dough, slightly sweetened. We can say about the same of the chestnut. Raw it is not good for much, though at a pinch it can be eaten; cooked, it deserves all the praise we give it, and I am sure you will back me up in this assertion. Here again we have a transformation of starch to sugar by the action of heat. Beans and peas, hard as bullets when dry, and far from pleasing to the palate, are unmistakably sweetened as soon as boiling water has worked upon their starch. Our farinaceous foods of sundry sorts behave in similar manner."
"Then do we make sugar," asked Claire, "whenever we boil a pot of potatoes or chestnuts or beans? I didn't know we were so clever; but I for my part shall not put on any airs, as it isn't very hard to make a pot boil."
"Man's ingenuity has devised a more effective means than heat alone for converting starch into sugar. The starch is boiled in water and, while it is boiling, there is added a small quantity of a powerful liquid called oil of vitriol or sulphuric acid. This causes the starch to turn to syrup, after which the oil of vitriol is of course removed. It has done its office. The substance thus obtained is soft, sticky, and nearly as sweet as honey; it is called starch-sugar, or glucose, and is much used by confectioners. As I have already told you, the sugarplums and other sweets that you buy at the candy shop are in most instances the product of this ingenious process of turning starch into sugar. And so you see the humble potato furnishes you with something besides the modest dish you find every day on the table.
"But that is not the whole story. Glucose, obtained as I have described, is exactly the same as the sweet part of ripe grapes. With potatoes, water, and a few drops of sulphuric acid there is artificially produced, in enormous boilers, the same sweet substance that nature manufactures by the action of the sun's rays on the full-grown grape. Now, since grape-sugar turns to alcohol by fermenting, starch-sugar ought to undergo a like transformation. As a matter of fact, in northern countries, where the climate is too cold for the vine, alcoholic liquors are made from starch that has first been changed to sugar. Such liquors bear the generic name of potato-brandy, though all seeds and roots rich in starch may be used in the same way as the potato."
"Let us now drop the subject of potato-brandy, which I have briefly touched upon to satisfy your curiosity, and return to matters of household economy. There are various starchy substances that are much used in making soup, chief among them being the starch of potatoes, which furnishes a nourishing and appetizing dish of this sort and is our most important, least expensive, and most widely distributed food product of its kind. Many of the starchy preparations bearing pretentious names are really nothing but this, at least in part. Other forms of the same essential substance appear more rarely on our tables, their higher price causing them to be reserved for dyspeptics and convalescents. Let us consider for a moment the chief of these.
"In South America there is cultivated a large farinaceous root called manioc, which in its natural state is a deadly poison to man, but which nevertheless furnishes material for excellent bread. First the root is reduced to pulp with a grater, after which the juice is squeezed out, and with the juice goes the poison, leaving a harmless substance rich in starch and serving as the principal article of food for the poor in a country too hot for raising wheat. This farinaceous substance is sold with us under the name of tapioca. A spoonful of tapioca is transformed by the action of boiling water into a rich jelly of exquisite fineness.
"The woods and meadows of our own latitude abound in certain plants known as orchids, remarkable for their oddly shaped flowers and for the two small tubers of the size of pigeons' eggs in the midst of the fine roots of the plant. These tubers contain starch. They are gathered in eastern countries, and flour made from them comes to us under the name of salep or salop. Prepared with hot water, it furnishes a gummy jelly suitable for the use of invalids.
"Palm-trees grow only in a hot climate. The trunk of a palm is a graceful column, without branches, of lofty height, tapering but little from the bottom to top, and crowned with an enormous tuft of large leaves. One of these trees, the sago-palm, has the heart of the trunk filled with a farinaceous pith which is removed after the tree is cut down. From this pith is obtained a starchy substance known as sago and differing only slightly from potato starch.
"These strange forms of starch, which excite our curiosity but are of no great use to us, must not make us forget the farinaceous matter furnished by our own leguminous plants, lentils, beans, and peas. You know the excellent thick soup we make of dried peas, and you doubtless also know how disagreeable are the hulls of this vegetable, tough as parchment and without taste or nourishment."
"Yes," replied Emile, "if it were not for those horrid hulls, dried peas would n't be at all bad."
"The hulls, however, are got rid of by pouring the soup into a colander, which retains the objectionable part and lets through the pure pulp. But in the process a certain quantity of nutritive matter mixed with the hulls is lost.
"Invention and experiment have done away with this loss. The peas are steeped a few minutes in boiling water to burst the hulls, after which the peas are dried in an oven and then made to pass between two millstones sufficiently far apart to remove the hulls without touching their contents. Thus freed of their tough exterior, the peas are ground to powder, which goes under the name of pea starch. In similar manner are obtained bean starch and lentil starch. All these preparations are used for making soup, and all have the qualities, without the defects, of the vegetables from which they are derived; that is, they are freed from the disagreeable hulls that fatigue the stomach to no purpose.