All eggs cracked in a home, restaurant, commissary, or other food-preparation facility, must be checked by a Shomer Shabbos to ensure that there are no blood spots. [In some locations, actual checking is performed by a non-Jew (who earns a reward for each blood spot found), and is merely overseen by the Mashgiach.] If a blood spot is found, the entire egg should be discarded. If the egg was mixed into other food before the blood spot was noticed, then as much of the eggs should be removed as possible, and the rest of the food may be served as kosher. Similarly, if eggs were put into food without being checked for blood spots, the food is b’dieved permitted.
In white eggs, blood spots are rather rare. They occur about once in every 500 eggs, and if the eggs are “candled” (as most eggs are), the end user will usually only find one blood spot in every 5,000 eggs. In brown eggs, true blood spots are also rare but the likelihood is 2 to 4 times as high as for white eggs. However, brown eggs have a relatively high incidence of something known as “protein spots” which are often mistaken for blood spots. Blood spots are red, have a symmetrical shape (round, oval, or lines), and tend to be found in the yellow of the egg, while protein spots are brown or off-white, are irregularly shaped in a way that is inconsistent with a drop of blood, and are usually found in the white of the egg. These protein spots – which are more noticeable in brown eggs than white ones because pigment from the brown shell “leaks” into the egg and collects at the protein spots – are permitted.
All forms of cooked eggs are assumed to require bishul Yisroel (participation of a Jew in the cooking). This includes soft or hard boiled eggs, fried eggs, omelets, scrambled eggs, and any other way to prepare eggs. Accordingly, if an event features “egg stations”, a Shomer Shabbos must light the fire at each one.
Liquid eggs are pasteurized at approximately 140 degrees Fahrenheit and require hashgachah to ensure that (a) the equipment used to process them was not previously used for non-kosher items, and (b) the minor ingredients added are all kosher. Similarly, hashgachah is required for peeled hard-boiled eggs, and for frozen fried eggs, due to bishul akum, ingredient, and equipment concerns. Many varieties of liquid eggs contain dairy ingredients. To make things more complicated, the same company may sell two varieties in similar cartons, where one is dairy and the other is pareve, and Mashgichim should carefully check each container.
The Gemara says that if eggs, onions, or garlic are peeled at left overnight, one should not eat them. Some accept and follow the Gemara at face value, others permit these foods if any minor ingredient was added to them (e.g., salt), and Rav Moshe Feinstein wrote that the Gemara does not apply if they were prepared for long-term storage (e.g., frozen, canned). In contrast, Rav Schwartz (and others) are of the opinion that the concerns raised by this Gemara do not apply nowadays, and accordingly cRc certified establishments do not concern themselves if eggs, onions, or garlic were peeled and left overnight.