On food and cooking the science and lore of the kitchen ( PDFDrive ) 45

withoutcurdling.
The Caseins The casein family includes four
differentkindsofproteinsthatgathertogether
intomicroscopicfamilyunitscalledmicelles.
Each casein micelle contains a few thousand
individual protein molecules, and measures
aboutatenthousandthofamillimeteracross,
about one-fiftieth the size of a fat globule.
Aroundatenthofthevolumeofmilkistaken
upbycaseinmicelles.Muchofthecalciumin
milkisinthemicelles,whereitactsasakind
of glue holding the protein molecules
together. One portion of calcium binds
individual protein molecules together into
small clusters of 15 to 25. Another portion
thenhelpspullseveralhundredoftheclusters
together to form the micelle (which is also
held together by the water-avoiding
hydrophobic portions of the proteins bonding
toeachother).
KeepingMicellesSeparate…Onememberof


the casein family is especially influential in
these gatherings. That is kappa-casein, which
caps the micelles once they reach a certain
size, prevents them from growing larger, and
keepsthemdispersedandseparate.Oneendof
thecapping-caseinmoleculeextendsfromthe
micelle out into the surrounding liquid, and
forms a “hairy layer” with a negative

electricalchargethatrepelsothermicelles.

A close-up view of milk. Fat globules are
suspended in a fluid made up of water,
individualmoleculesofwheyprotein,bundles
of casein protein molecules, and dissolved
sugarsandminerals.
…AndKnittingThemTogetherinCurdsThe
intricatestructureofcaseinmicellescanbe
disturbedinseveralwaysthatcausethe