Some recipes tell me to salt onions as soon as they hit the pan and others insist on salting at the end, and the results are noticeably different even though the quantity is the same.
What is the salt doing differently depending on when it goes in?
Accepted Answer
Salt draws water out of the cells by osmosis, and when that happens decides what the onion does next.
Salt early and the onions release water into the pan. That water keeps the temperature at boiling point until it evaporates, so the onions soften and sweat rather than brown. Good for a base where you want them translucent and sweet.
Salt late and the surface stays drier for longer, so the pan gets hotter sooner and you get colour and caramelisation rather than softening.
Neither is correct in general. Salting early for a soffritto and late for browned onions on a burger are both right for what they are after.
Worth separating caramelisation from the Maillard reaction here, because recipes use the words interchangeably and they are different chemistry.
Caramelisation is sugars breaking down on their own, and it needs quite high temperatures. Maillard is sugars reacting with amino acids and starts lower.
Browned onions are mostly Maillard with some caramelisation. It matters practically because the "caramelised onions in ten minutes" recipes are not doing either properly. Genuinely browned onions take the better part of an hour, and anything faster has used heat to fake the colour.
A small addition: a pinch of bicarbonate raises the pH and speeds Maillard considerably. It does cut the time down, at the cost of a slightly slippery texture if you overdo it.
The discussion on each answer is open to members.
Join free to read the rest