On Food and Cooking

composed of straight-chain saturated fatty
acids fall into an ordered solid structure —
the process has been described as “zippering”
— more readily than do kinked unsaturated
fats. Animal fats are about half saturated and
half unsaturated, and solid at room
temperature, while vegetable fats are about
85% unsaturated, and are liquid oils in the
kitchen. Even among the animal fats, beef and
lamb fats are noticeably harder than pork or
poultry fats, because more of their
triglycerides are saturated.
Double bonds are not the only factor in
determining the melting point of fats. Short-
chain fatty acids are not as readily “zippered”
together as the longer chains, and so tend to
lower the melting point of fats. And the more
variety in the structures of their fatty acids,
the more likely the mixture of triglycerides
will be an oil.