21: 



HISTORY OF THE VEGETABLE KINGDOM. 



menting beer, Tliis addition occasions fully as 

 speedy a fennentation as leaven, and it is not 

 nearly so apt to give the bread a sour flavour. 

 About tlie end of the 17th century the bakers of 

 Paris began to substitute yeast for leaven. The 

 practice was discovered, and declaimed against. 

 The faculty of medicine, in 1668, declared it pre- 

 judicial to the health; and many years elapsed 

 before the bakers were able to convince the pub- 

 lic that bread raised by means of yeast is better 

 than that fermented by leaven. Barm is now 

 employed in preference to leaven in every civil- 

 ized country. In this country the yeast used 

 by bakers is made artificially, chiefly from pota- 

 toes. The process, according to Dr Thomson, is 

 nearly as follows : A certain quantity of salt is 

 dissolved in water, the temperature of which va- 

 ries, according to circumstances, fi'om 70° to 100°. 

 Yeast is mixed with this water, and then a por- 

 tion of flour is added, but always less than is ul- 

 timately employed in forming the finished dough. 

 The mixture is covered up, and set apart in a 

 warm place. Fermentation begins to be evident 

 in about an hour. The sponge, so the imperfect 

 dough is called, begins to swell up in consequence 

 of the evolution of carbonic acid -gas. This gas, 

 being confined by the adhesive nature of the 

 gluten, heaves up the sponge to twice its original 

 bulk. Being no longer capable of containing 

 this pent up gas, it bursts, and subsides. This 

 alternate rising and falling of the sponge might 

 be repeated a great many times ; but unless the 

 baker stops it after the second, or at the utmost 

 the third dropping of the sponge, the bread inva- 

 riably proves sour ; he therefore, at this period, 

 adds to the sponge the remaining quantity of 

 flour, water, and salt, and incorporates these new 

 materials with the sponge by a long and labori- 

 ous course of kneading. After this the dough is 

 left to itself for a few hours, during which time 

 it continues in a state of acti\'8 fermentation, 

 diffused through every part of it. It is then 

 subjected to a second, but much less laborious 

 kneading, in ordes to distribute the imprisoned 

 gas as equally as possible through the whole 

 dough. It is now weighed out into the portions 

 requisite to form the kinds of bread desired. 

 These portions are shaped into loaves, and set 

 aside for an hour or two in a warm situation. 

 The fermentation still goes on, and gi'adually ex- 

 pands the mass to double its former bulk. They 

 are now put into the oven and Ijaked into loaves. 

 The mean heat of the oven is about 448°. This 

 heat immediately stops the fermentation; but 

 the gas ah-eady generated is swelled out by the 

 heat, and gives the loaf its characteristic vesicu- 

 lar structure. When bread is taken out of the 

 oven it is lighter than when put in, from the 

 evaporation of a portion of moisture during the 

 baking. A portion of the starch, also, is con- 

 verted into sugar. 



Kye. 



Rye ( sccale cereale). This 

 grain has an appearance some- 

 thing intermediate between 

 wheat and barley. The ear is 

 bearded, and the stem tall and 

 slender. Eour species of this 

 plant are enumerated, secale 

 mllosum, orientale, creticum, and 

 cereale. The last only is cul- 

 tivated in Britain. The rais-, 

 ing of rye was formerly much 

 more practised in this country 

 than at present. Two centu- 

 ries ago rye flour, either alono 

 or mixed with wheaten flour, 

 formed the common bread of 

 this country. Now this mix- 

 ture is onlj' partially used. At 

 present rye is cultivated by 

 our farmers principajly that they may draw from 

 it a supply of green food for their flocks. For 

 this purpose the plants, which are sown in No- 

 vember, are eaten early in the spring, before they 

 begin to spindle, which they will do towards the 

 end of March. After this stage of the gi'owth 

 has taken place, the succulent quality of the 

 blade is impaired, it becomes coarse and harsh, 

 and is no longer agreeable to animals. When 

 rye is left to ripen its seeds, these are, for the 

 most part, applied in this country to purposes 

 distinct from human food ; the principal use to 

 which the grain is put being the prepai-ation of 

 a vegetable acid, to be employed by tanners in 

 an operation which they call raisin ff, and where- 

 by the pores of the hides are distended, so as to 

 dispose them the more readily to imbibe the tan- 

 ning principle of the oak-bark, which is after- 

 wards applied. Rye, when parched and ground, 

 has been recently used as a substitute for coffee. 

 It would be difiicult, however, to convince any 

 one accustomed to the use of this grateful beve- 

 rage, that the grain of home production is ever 

 hkely to take place, at least to any extent, of 

 the fragrant Mocha bean. In fact rye contains 

 neither the aromatic nor stimulating properties 

 which render cofl'ce so grateful. 



Rye straw is useless as fodder, but foi-ms an 

 excellent material lor thatching, and is so suit- 

 able for stuffing horse-collars, that saddlers wiU 

 usually pay for it a very good price. 



The secale cereale, which is said to be a native 

 of Candia, was introduced into England many 

 ages ago. There are two varieties of this species, 

 occasioned more probably by difference of cul- 

 ture than by any inherent variation in the plants ; 

 one is kno^vn as winter, and the other as spring 

 rye. 



It was formerly usual to bow rye together 

 with an early kind of wheat. The harvested 

 grain, thus necessarily intermixed, was termed 

 meslin, from miscellanea ; it also obtained the 



