Ice cream is more American than apple pie. Thomas Jefferson
made ice cream at Monticello. George Washington loved ice
cream. It is said that ice cream is not food, it is medicine,
capable of curing melancholy and lifting spirits, drowning
sorrows and bringing smiles to the most defeated of little
Ice cream at its simplest is made of milk,
sugar, cream, and
some flavoring, such as fruit puree or
ingredient in addition to those is air, without which ice
cream would not be the special treat it is.
In the U.S., ice cream must contain at least 10% milk fat, and
at most 50% air, and must weigh at least 4.5 pounds per gallon.
Ice creams termed "premium" and "super premium" have higher fat
content (13% to 17%) and lower air content (called "overrun" in
the ice cream trade).
Sherbets have a milk fat content between one and two percent,
and usually have more sugar. Often flavored with fruit, a
gallon of sherbet weighs a minimum of six pounds.
Water ices and sorbets are similar to sherbet, but contain
no dairy products.
Gelato is made of sugar, milk, cream, egg yolks, and flavorings,
and is usually served semi-frozen.
Ice Cream Ingredients
The milk and cream are sources of butterfat, proteins, and milk
Butterfats add rich flavor, smooth texture, body, and good
melting properties. The triglycerides in butterfat
melt over a wide range of temperatures, so there is always some
bit of solid and some liquid butterfat. Some of the butterfat
almost turns into butter while the ice cream is churned, adding to
the unique texture of ice cream.
The proteins help to incorporate air into the mixture, helping
to form small bubbles of air. They modify the texture of the
ice cream in other ways as well, making it chewier, and giving
it body. The proteins also help to emulsify the fats, keeping
the fat globules suspended in the mix.
The proteins coat each fat globule, keeping them from sticking
together. However, making the globules stick together in chains
and mesh-like structures is important in giving ice cream its
texture and ability to hold air, and its ability to stay firm
as the ice inside melts. Emulsifiers, such as the
in egg yolks, stick their fatty acid ends into the fat globules,
and prevent the proteins from completely coating the fat. This
balance between proteins and emulsifiers allows the fat globules
to chain and stack, without flowing together.
The milk sugar lowers the freezing point of the water in the
ice cream. Adding extra sweeteners, such as sugar and corn syrup,
also have this effect. This ensures that a portion of the water
never freezes, keeping the ice cream from becoming a solid chunk
of ice. Added sweeteners are inexpensive, and make up about 15%
of the mix by weight. The use of high-fructose corn syrup will
reduce the freezing point further than sugar, resulting in a softer
Ice Cream Additives
As ice creams move down the scale from premium, getting lower
in fat and incorporating more air, ingredients are added to
make up for the loss of creamy texture, rich "mouth feel",
and to help keep all of the extra air whipped up.
Emulsifiers such as the monoglyceride
and related diglycerides help to keep the milk fat in suspension,
and limit the growth of ice crystals. Other emulsifiers such as
perform similar functions.
Emulsifiers have a significant effect on making the fat globules
stick together in chains, rather than flowing together in larger
globules, or staying separated as tiny ones. This adds to the
structure of the ice cream, and affects the texture and the
ability to incorporate air into the mixture.
Gums such as
locust bean gum,
help to prevent ice crystals from forming during freezing and
re-freezing after a trip from the grocery store. They also
have a "mouth feel" similar to milk fat, so the milk fat is
not missed as much in low fat ice creams. Like emulsifiers,
they also aid in keeping the air whipped into the mix. Gums
keep the ice cream from becoming grainy due to crystals forming
from either ice or lactose.
Some ice creams contain sodium
citrate to decrease the tendency of fat globules to coalesce,
and to decrease protein aggregation. This results in a "wetter"
ice cream. The citrates and phosphates are both used for this
effect. Calcium and magnesium salts have the opposite effect,
making a "dryer" ice cream.