Onion

Over 80 percent water by weight, held under pressure in turgid cells. Heat destroys the cell membranes and that water leaves within 15 to 20 minutes. One kilogram of sliced onion releases 400 to 600 ml. Plan the liquid of a braise around this, not around how dry the tray looks at the start. Onions store carbohydrate as fructans, not as starch. Long heat breaks these into free fructose and glucose, which then react with the amino acids of the onion. This is a Maillard reaction, not caramelisation: it needs no added sugar and it runs far below the 186 degrees C at which sucrose melts. The stage matters. Deep gold gives pyrazines, thiols and free glutamate: savoury and roasted. Darker gives melanoidins and maltol: sweet and fudge-like. Those late compounds have low volatility and they mask high-volatility aromatics such as citral. Stop at deep gold in any dish built on fresh herbs. Collapsed onion also carries pectin, which thickens a sauce with no added starch.