98 THE POTATO AND ITS COMMERCIAL PRODUCTS. 



jelly; and if there be not a quantity of starch in the cells, it will not burst. 

 But if the number of grains or their size be very great, the potato is broken 

 on all sides by the expansion of the little masses of jelly, and mealiness is 

 produced. 



Frost-bitten potatoes are sweet, from the spontaneous conversion of their 

 starch into sugar. The same effect takes place when potatoes sprout in 

 the spring, and they are consequently of less value as food. Potatoes 

 should be stored in the fall with a portion of earth adhering to them, or at 

 least mixed with them : this keeps them a little damp, and prevents the 

 action of the atmosphere from causing a too powerful evaporation. 



The French method of cooking potatoes affords a most agreeable dish. 

 The potatoes are peeled, piped and cut into thin slices, then thrown into a 

 frying-pan containing an abundance of hot lard. As soon as they become 

 brown and crispy, they are turned into a colander to drain, then sprinkled 

 with salt, and served up as hot as possible. 



Starches are highly hygrometic : thus, ordinary potato-starch can com- 

 bine with 3, 5, 11, and 16 equivalents of water. The starch as extracted 

 from the potato contains from 35 to 25 per cent, when kept in a damp atmo- 

 sphere, and 18 per cent, when stored in a dry place. 



It is easy to distinguish starch which contains (say) 18 per cent, from 

 that which contains 35 per cent., by placing a small quantity on a metallic 

 plate heated to 212° ; for the starch with 18 per cent, will fly about, whilst 

 that with 35 agglomerates and forms hard lumps. In fact, it is by means of 

 this property of potato-starch that large quantities of artificial tapioca are 

 made on the Continent. 



In 1859 we imported 40,185 cwt. of potato-flour from the Continent, 

 593 cwt. of potato arrowroot, 7,832 cwt. of starch, 1,524 cwt. of semolina 

 (chiefly potato), and 270 cwt.. of potato-starch gum ; making, with 588,910 

 cwt. of potatoes imported, an aggregate value for foreign potato products of 

 138,500?., exclusive of what is produced here. The imports of potatoes vary 

 considerably according to the condition of our own crop : thus, in 1855, If 

 million cwt. of potatoes were imported. 



A great deal of potato-starch is made in America. At Stowe, in 

 Vermont, there are five factories, which each consume about 20,000 bushels 

 of potatoes per annum, and 8 lb. of starch is the yield of each bushel. 



Dextrine. — This substance, which in the Board of Trade returns is with 

 great propriety termed starch gum, has been called dextrine on account of 

 its solution possessing the property of effecting the right-handed rotation 

 of the plane of polarisation by a ray of light. Dextrine is prepared 

 either by torrifying potato-starch, or by the action of heat aided by a 

 minute portion of nitric acid. The latter method yields the most soluble 

 and least-coloured product. 



In the process of breadmaking, a portion of wheat-starch is converted 

 into dextrine (torrified or gummy starch) ; of which, according to Vogel, 

 wheat-bread contains about 18 per cent. In the process of brewing, the 

 starch of the malt is converted into dextrine and sugar by the action of 

 diastase. 



