Butterfat or milkfat is the fatty portion of milk. Milk and cream are often sold according to the amount of butterfat they contain.
The fatty acids of butterfat are typically composed as follows (by mass fraction):
As shown above, the composition of fats in milk is usually discussed in terms of the fatty acids. Fatty acids do not occur as such in milk (and rarely in any food). Instead, they are incorporated into compounds called triglycerides.
U.S. standards
In the U.S., there are federal standards for butterfat content of dairy products. Many other countries also have standards for minimum fat levels in dairy products. Commercial products generally contain the minimum legal amount of fat with any excess being removed to make cream, a valuable commodity.
Milks
Skim milk contains less than 0.5% fat, typically 0.1%
Lowfat milk contains between 0.5–2% fat; 1% and 2% varieties are widely marketed
Whole milk contains at least 3.25% fat
Cheeses
Dry curd and nonfat cottage cheese contain less than 0.5% fat
Lowfat cottage cheese contains 0.5–2% fat
Cottage cheese contains at least 4% fat
Swiss cheese contains at least 43% fat relative to the total solids
Cheddar cheese contains at least 50% fat relative to the total solids
Frozen desserts
sherbet contains 1–2% fat
Lowfat ice cream, also called ice milk, contains no more than 2.6% fat
Ice cream contains at least 10% fat
Frozen custard, like ice cream, contains at least 10% fat, but it also must contain at least 1.4% egg yolk solids
Creams
Half and half contains 10.5–18% fat
Light cream and sour cream contain 18–30% fat
Light whipping cream (often called simply "whipping cream") contains 30–36% fat
Heavy cream contains a minimum of 36% fat
Manufacturer's cream (not federally regulated) contains 40% fat
Butter (including whipped butter) contains at least 80% fat
