On food and cooking the science and lore of the kitchen ( PDFDrive ) 577
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into the released cell fluids and any added
water.Theycan’tsimplyre-formtheirgelfor
acoupleofreasons.Pectinmoleculesinwater
accumulate a negative electrical charge, so
theyrepeleachotherratherthanbondtoeach
other; and they’re now so diluted by water
molecules that even if they did bond, they
couldn’t form a continuous network. They
needhelptofindeachotheragain.
Thecookdoesthreethingstocookedfruit
tobringpectinmoleculesbacktogetherintoa
continuousgel.First,headdsalargedoseof
sugar,whosemoleculesattractwater
moleculestothemselves,thuspullingthe
waterawayfromthepectinchainsandleaving
themmoreexposedtoeachother.Second,he
boilsthemixtureoffruitandsugarto
evaporatesomeofthewaterawayandbring
thepectinchainsevenclosertogether.Finally,
heincreasestheacidity,whichneutralizesthe
electricalchargeandallowsthealoofpectin
chainstobondtoeachotherintoagel.Food
scientistshavefoundthattheoptimal
conditionsforpectingelationareapH
between2.8and3.5—abouttheacidityof
orangejuice,and0.5%acidbyweight—a
pectinconcentrationof0.5to1.0%,anda
sugarconcentrationof60to65%.
PreparingPreservesPreservemakingbegins
with cooking the fruit to extract its pectin.
Quince,apples,andcitrusfruitsareespecially
rich in pectin and often included to
supplementotherpectin-poorfruits,including
most berries. The combination of heat and
acid will eventually break pectin chains into
pieces too small to form a network, so this
preliminary cooking should be as brief and
gentle as possible. (If a sparkling, clear jelly
is desired, then the cooked fruit is gently
strained to remove all solid particles of cell
debris.) Then sugar is added, supplemental
pectin if necessary, and the mixture rapidly
brought to the boil to remove water and
