On food and cooking the science and lore of the kitchen ( PDFDrive ) 1008

for energy, and produce carbon dioxide gas
and alcohol as by-products of that
metabolism. The overall equation for the
conversion that takes place in yeast cells is
this:
C6H12O6 2C2H5OH+2CO2(1moleculeof
glucosesugaryields2moleculesofalcohol
plus2moleculesofcarbondioxide)
Inmakingbeerandwine,thecarbondioxide
escapesfromthefermentingliquid,and
alcoholaccumulates.Inmakingbread,both
carbondioxideandalcoholaretrappedbythe
dough,andbothareexpelledfromthedough
bytheheatofbaking.
Inanunsweeteneddough,yeastsgrowon
thesingle-unitsugarsglucoseandfructose
andonthedouble-glucosesugarmaltose,
whichenzymesintheflourproducefrom
brokenstarchgranules.Asmallamountof
addedtablesugarinadoughwillincrease
yeastactivity,whilealargeamountdecreases
it(seesweetbreads,p.546),asdoesadded


salt.Yeastactivityisalsostronglyaffectedby
temperature:thecellsgrowandproducegas
mostrapidlyatabout95ºF/35ºC.
Inadditiontoprovidingcarbondioxidegas
toinflatethedough,yeastsreleaseanumber
ofchemicalsthataffectthedough
consistency.Theoveralleffectisto

strengthentheglutenandimproveits
elasticity.
FormsofBaker’sYeast Commercialyeastis
sold to home and restaurant cooks in three
commonforms,eachadifferentgeneticstrain
ofS.cerevisiaewithdifferenttraits.
Cakeorcompressedyeastisamoist
blockoffreshyeastcells,directfromthe
fermentationvat.Itscellsarealive,and
producemoreleaveninggasthanthe
otherforms.Cakeyeastisperishable,
mustbekeptrefrigerated,andhasabrief
shelflifeofonetotwoweeks.
Activedryyeast,whichwasintroduced