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B R E
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altered by acids. Accordingly the heft practicaldyers have employed acids and tin in their at-tempts to fix this beautiful colour. (See thearticle Dyeing.)
Bread is a light porous fpungy fubftance, pre-pared by fermentation and baking from the flourof certain farinaceous feeds, efpecially wheat,and is the principal fuftenance of man in thetemperate regions of the Northern hemifphere.
It is not likely that the unprepared grains ofwheat were ever the habitual food of man; forby maftication the gluten that they contain coa-lefces into a tough elaftic mafs, equally un-palatable and indigeftible. We read howeverof corn being fitted for ufe on fudden emer-gencies merely by parching, and this was pro-bably the fimplelt and earlieft method of con-verting it into human food. The next advancewas to pulverize the grains in a mortar or handmill, to feparate the coarfe bran from the finerparticles, and by the addition of water or milkto form thefe latter into a tough pafte, whichbeing rolled into flat thin cakes was renderedeatable by toafting on a hot ftone or plate ofmetal. The Romans in the early period of theirrepublic, and alfo the Carthaginians, appear,like the modern Italians , to have confumed theircorn pincipally in the ftate of polenta or furmety,in which the wheat undergoes no further pre-paration than being boiled till the grains are•fwollen confiderably and are become tender. Byall thefe methods the molt prefling obj edition tothe ufe of wheat, namely, its forming a toughglutinous mals during maftication, was com-pletely got rid of, the action of fire alone, or offire combined with water, producing the necef-fary change in the.gluten with which this fpeciesof corn abounds. Still however it was deftituteef that peculiar lightnel's and flavour which itacquires when converted into bread, properlyfpeaking, by a flight degree of fermentation.
The flour of wheat is compofed of fecula orftarch, and a gluten exadtly refembling in itsproperties and compofition the gluten of blood,together with a fmall proportion of faccharinemucilage. When kept dry, and at a tempera-ture not exceeding that of boiling water, itappears incapable of undergoing any fpontaneouschange, and continues in the ftate of a fineimpalpable powder, but if mingled graduallywith a fufficient quantity of water to form athin tenacious pafte, and expofed for a day ortwo to a warm air, the procefs of fpontaneousdecompofition begins to fhew itfelf. The colourof the mafs becomes yellow, the flat fub-nau-
feous fmell becomes acidulous and fenfibly pun-gent, and the bulk is fomewhat increafed, owingto the difengagement of fmall bubbles of car-bonic acid gas: thefe figns of fermentation pre-fently becomes more and more apparent, andthe pafte pafles rapidly into the putrefadfiveftate, exhibiting the ufual figns of this fpeciesof decompofition, modified however by theacetous fermentation which takes place at thefame time.
This change appears to be certainly begunand principally carried on by the gluten; al-though the panary fermentation, as it has beencalled, is fuppofed by many chemifts to be pro-duced by the contemporaneous action of threediftindt fermentations, to which the three ele-ments of wheaten flour are refpedtively fubjedt.They imagine the vinous fermentation to takeplace in the faccharine mucilage, the acetous inthe ftarch, and the putrefadtive in the glutenat the fame time, and from the modification ofeach by the others, they confider that peculiaraction to originate which converts pafte into,bread. Againft this opinion however the fol-lowing objedtions may be urged. In the firftplace, the quantity of faccharine mucilage is foextremely fmall as to produce no fenfible effecton the whole mafs, and what little there isprobably pafles immediately into the acetousfermentation. Secondly, the temperature thatis required for bread-making is confiderablylower than that at which ftarch diflolves inwater, and where this is the cafe no alterationwill take place, even in a long courfe of time:this is clearly fhoxvn by the ufual procefs offtarch-making, in which the bruiled wheat isfermented for feveral days in large vats, in orderto deftroy the gluten, after which the ftarch isprocured by fimple depofition from the wafh-ings of the refidue. So eflential is the prefenceof gluten to the preparation of bread, that itsperfedtion is almoft exadtly in proportion to thequantity which it contains of this ingredient.Hence wheat yields the beft bread, becaufe itis compofed of a larger proportion of glutenthan any other grain, and hence rice, millet andoats are incapable of being converted into breadbecaufe they contain little or none of it. Infurther confirmation of this it may be remarkedthat if the gluten of wheat (procured by Amplewaffling as defcribed under the article Gluten )-be incorporated by careful kneading with rice-flour, a fermentable cohefive pafte is thus pro-duced, from which perfedt bread may be madein the ufual manner. It would be a curiousenquiry, and one of no fmall importance to the