On food and cooking the science and lore of the kitchen ( PDFDrive ) 1534
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individualmoleculesinthatsubstance
becomesforcefulenoughthattheelectrical
forcesholdingtheminplaceareoverpowered.
Thefixedstructurethenbreaksup,leavingthe
moleculesfreetomovefromoneplaceto
another.However,mostofthemoleculesare
stillmovingslowlyenoughthattheyremain
influencedbytheforcesthatonce
immobilizedthem,andsotheyremainloosely
associatedwitheachother.They’refreeto
move,butmovetogether.Thisfluidbut
cohesivephaseisaliquid.
Gases
Ifthetemperaturecontinuestoriseandthe
moleculesmovewithakineticenergyhigh
enoughthattheycanbreakawayfromeach
other’sinfluencecompletelyandmovefreely
intotheair,thesubstancebecomeadifferent
kindoffluid,agas.Themostfamiliar
transitionfromtheliquidphasetothegas
phaseisboiling,inwhichwetransformliquid
waterintobubblesofwatervapor,orsteam.
Lessobvioustotheeye,becauseit’sso
gradual,istheevaporationofwaterat
temperaturesbelowtheboilingpoint.The
moleculesinaliquidmovewithawiderange
ofkineticenergies,andasmallportionofthe
moleculesinroom-temperaturewaterare
movingfastenoughtoescapefromthe
surfaceandmoveintotheair.
Infact,watermoleculescanevenescapeas
agasfromsolidice!Thisdirect
transformationofasolidintoagasiscalled
sublimation,andisthecauseofthat
deteriorationinfoodsknownas“freezer
burn,”inwhichcrystallinewaterevaporates
intothefreezer’scold,dryair.Freeze-drying
isacontrolledversionofthesameprocess.
ManyFoodMoleculesCan’tChangePhase
Mostofthemoleculesthatthecookworks
