Egg

Eggs are frequently used as a binding agent in period recipes. While redacting, you should keep in mind that eggs were smaller during period, and adjust the number of eggs accordingly. Alternatively, use bantam eggs. All sorts of eggs can be used in cooking, although the cholesterol content, and egg white:egg yolk ratio may vary depending on the egg. Duck and goose eggs are much larger than chicken eggs, and there is more yolk in them, so often on large duck or goose egg is equivalent to two small chicken eggs.

Eggs were also used as period hydrometers while brewing. The amount of egg visible above the liquid determined the density.

You can tell if an egg has gone rotten by placing it in a bowl of water: if it floats it is bad, if it sinks it is good. This is because when the egg starts to go off, a byproduct of this is gas which remains trapped in the egg, and thus it floats.

Eggs are often thought of as a short term product, but in fact can be stored for long periods of time, in a cool cellar, it is simply the very unpleasant smell of hydrogen sulfide (rotten egg gas) that makes many people unwilling to keep eggs long enough that any significant percentage has gone off. Coating eggs in vaseline will block the pores of the egg, increasing their longevity to a point where many of your eggs are still good after a year. Vaseline (petroleum jelly) is obviously a modern product, but various waxes, tars, resins and glues were available in medieval times, although their useage may not have been recorded, even if used. The most efficient way to keep a good supply of eggs is to keep a few hens.

Egg yolks and whites are used in egg tempera painting techniques and in illumination.