What is the fine-grained topic of the following text: First of all it is useful to say that there are two types of eggs: those of Category A, which are fresh eggs and have the characteristic of having an air chamber not higher than 6 mm and 4 mm for extra ones; and Category B eggs, ie those not intended for large-scale distribution but for the processing industry (for example, producers of mayonnaise and biscuits, which must be pasteurized before using them for legal purposes). Only return the topic.
Types and classifications of eggs.