An egg drink is a fountain drink that incorporates an egg, along with syrups, phosphate or other souring agents, and carbonated water. It is very important to note that an egg cream is not an egg drink, as it does not actually contain any egg (or cream!) See egg cream for more discussion.
A historical (1901) description of how to prepare egg drinks is as follows:
Serving Egg Drinks
The usual manner of preparing egg drinks is first to crack the egg shell on a 12-ounce glass by striking it on the edge of the latter, then break the egg with both hands, so that the contents will fall unbroken into the glass, and throw the shell away. If the egg should happen to be spoilt, put the glass quickly out of the way and break a fresh egg into another glass. Then add the syrup or syrups and solution of acid phosphates, if a "phosphate" is being served, and about 2 ounces of cracked or shaved ice, or a small lump of ice. Then put the shaker over the glass and shake thoroughly. Then set the whole down on the counter with the glass up, so the liquid is in the shaker. Now turn in the fine stream of carbonated water into the latter until about two-thirds full, and fill entirely with the coarse stream.
Pour the liquid from shaker to glass and back again, holding the shaker and glass but a few inches apart, and pouring rapidly, repeating three times, leaving the mixture in the glass at the last pouring. The drink may be topped nicely with foam by pouring the last of the liquid from the shaker to the glass by holding them some distance apart and pouring slowly. Finally shake a little finely-grated nutmeg upon the surface of the beverage, and it is ready to serve.
The glass used in shaking must be one of the thick heavy kind, as the thin, light ones, are obviously not strong enough. Instead of using a shaker and glass for shaking, the operator may use one of the shakers now made with a cover.
Some prefer to strain the drink. Strainers are made for this purpose. The shakers with covers have strainers in the latter, so that extra strainers are not necessary. If too much ice is not used, a strainer is unnecessary.
There are many who make egg drinks by mixing the egg, syrup, "acid phosphates," if latter is used, and about 2 fluid ounces of plain water (ice water preferred) in a shaker with cap, agitating thoroughly, pouring out through the strainer into a 12-ounce glass, nearly filling the latter with the coarse stream of carbonated water, topping with the fine stream and sprinkling on the nutmeg. The water is added for the purpose of facilitating agitation. Charged water cannot be used for this purpose.
"Throwing" an egg drink, as it is termed, is to be deprecated, as it has a tendency to make a flat, insipid beverage.
Eggs used for preparing drinks should be washed perfectly clean and dried.