render
Slowly cook a fatty ingredient (bacon, salt pork, duck skin) to melt out its fat, leaving crisped solids behind. The rendered fat is not a by-product to be poured away -- it is usually the cooking medium for whatever comes next, and it carries the flavor of what it came from.
How to do it
For something like bacon or pancetta, starting in a cold pan is especially useful -- put the food in before turning on the heat, then bring the temperature up gradually so the fat begins melting before the lean portions brown too aggressively. Keep cooking at moderate heat, adjusting as needed. Once enough fat has pooled, the remaining pieces start effectively frying in their own rendered fat. Pull out any crisp solids with a slotted spoon if you want them separately, and strain the fat if you want to save it.
Common pitfalls
- Starting too hot -- the exterior can burn before much fat has actually rendered out.
- Leaving the heat too low the whole time -- the fat renders fine, but real browning may never develop.
- Leaving rendered solids in the pan while cooking whatever comes next -- they can burn.
- Discarding the rendered fat automatically -- bacon, duck, or chicken fat is a genuinely useful cooking ingredient on its own.
Why it works
Animal fat is stored inside cells and connective tissue. As the temperature climbs, the solid fat melts and the surrounding cell structures weaken enough to let the liquid fat escape. Different fats melt across different temperature ranges because their fatty-acid makeup varies. Once the surrounding tissue has lost enough moisture, its surface temperature can climb high enough for Maillard browning and crisping to take over -- so rendering and browning overlap but aren't the same step: rendering removes the fat, and the higher heat that follows is what crisps what's left.
Equipment
A heavy skillet or saucepan works well -- cast iron holds heat steadily, and stainless steel makes it easy to watch the browning as it happens. For a large amount of fat, rendering can also be done gently in a Dutch oven or a low oven. A fine-mesh strainer is worth having if you're planning to save the fat afterward.