Why does vinegar curdle milk?
Vinegar is a dilute acetic acid. ACID CURDLING In normal conditions milk has a ph of about 6.5-6.7 and at this ph value the casein is without protons, it has a negative charge and therefore the casein micelles are relatively soluble, because they repel each others. In an acid ambient milk coagulates, because casein has its isoelectric point at 4.6 ph, that is at this ph value it has a quantity of positive charges equal to the quantity of negative charges and the positive part of each “micelle” is attracted by the negative part of the others, causing the formation of ionic bonds among the “micelle” working against the dipole-dipole bonds with water, so that the protein precipitates in the form of demineralized casein and in the solution remain soluble calcium salts.
