Fat is the most calorie-dense food there is, at roughly 9 kcal per gram against 4 for protein or carbohydrate, and it is the thing a survival diet most reliably runs short of. It is also, rendered properly, one of the few foods that keeps for months without refrigeration, canning or chemicals.
Rendering is simply melting fat gently enough to separate the pure fat from the connective tissue, water and protein it came packed with. Those impurities are what make raw fat spoil; take them out and what remains is stable.
Why it is worth doing
- Cooking fat that keeps. Months at room temperature, and it does not need refrigeration to stay good.
- Calories where you need them. A jar of tallow is dense, stable stored energy.
- Candles and lamps. See the energy and light chapter; tallow candles are the traditional answer to a dark winter.
- Soap. Fat plus lye is soap, and this is the fat.
- Waterproofing and leather dressing.
- It costs nothing. Butchers frequently give suet and back fat away, or sell it very cheaply, because most customers do not want it.
Which fat, and what it becomes
Harder fat makes better candles. If the intention is light rather than food, ask specifically for beef suet.
Wet rendering, the better method
Water is added to the pan. It prevents the fat scorching, and it gives the impurities somewhere to go.
- Chill the fat in the fridge or freezer until firm. It is far easier to cut.
- Trim off any meat, blood or gristle. Everything that is not fat will eventually be what makes it go off.
- Cut small, or mince it. Small pieces render faster and more completely. A mincer is worth using if you have one.
- Put the fat in a heavy pan with water, roughly one part water to four parts fat, and a tablespoon of salt per kilogram. The salt draws impurities out into the water.
- Heat gently. Aim for a bare simmer. The target is around 104 to 121°C in the fat itself; the water boiling off keeps it near the lower end early on.
- Cook slowly, stirring occasionally, for two to four hours. The fat becomes clear, and the solid pieces shrink, brown and float.
- When the bubbling slows and the solids sink or turn golden, it is done. The bubbling is the water leaving; when it goes quiet, the water has gone.
- Strain through muslin into a clean container.
- Let it cool and set. The fat rises and solidifies; the water with the impurities in it stays below.
- Lift the fat cake off, scrape the underside clean, and discard the water.
- For a whiter, more neutral result, repeat with fresh water and salt. Two or three rounds gives an almost odourless white fat suitable for soap, skincare and candles.
The solids left behind are cracklings and are worth eating. Drain, salt, and treat them as scratchings.
Dry rendering
No water. Faster, simpler, and gives a slightly nuttier, more strongly flavoured fat.
Same preparation, then heat gently in a heavy pan or a slow oven at low temperature, stirring often, until the fat has run and the solids are golden. Strain and cool.
The risk is scorching, which is why the pan must be heavy, the heat low, and the stirring frequent. Once fat scorches, the flavour is in it permanently and it will not come out.
Dry rendering is fine for cooking fat. Use wet rendering for anything intended to keep a long time, or for soap and candles, because the residual impurities are what limit shelf life.
Storing it
- Airtight, clean, dry containers. Glass jars are ideal. Fill while just warm and liquid, then seal once cool.
- Cool and dark. Light and warmth both accelerate rancidity.
- Keep water out. This is the main thing. Any trapped water gives mould somewhere to grow, and a jar with a drop of water in the bottom will spoil while the rest of the batch keeps perfectly.
- Always use a clean dry spoon. Crumbs and moisture introduced from the pan are how a good jar goes off.
| Storage | Keeps |
|---|---|
| Cool room temperature, sealed | Several weeks to a few months |
| Refrigerated | Several months |
| Frozen | A year or more |
| Wet-rendered, purified, cool and dark | Longest of the above at each condition |
Well-rendered tallow is one of the most shelf-stable foods you can make, because it is a saturated fat with essentially no water in it. Its enemies are water, air, light and heat, in that order.
Rancidity
Fat goes off by oxidation rather than by microbial spoilage, so the signs are different from most foods.
It smells wrong. Rancid fat smells of old crayons, stale nuts, oil paint, or in the worse cases of rotten meat. Fresh rendered tallow smells faintly of beef and pleasant; lard smells of very little.
Trust the smell. This is one of the cases where your nose is a genuinely reliable instrument, unlike the canning situation in recognising canning failure. If it smells bad when you take the lid off, discard it.
Rancid fat is not acutely poisonous, and it is unpleasant and the oxidation products are not good for you. In a shortage it is tempting to use it anyway; better to use it for soap, candles or leather dressing, where rancidity does not matter, and keep the good fat for food.
Preventing it:
- Render well, so there is little protein or water left to start the process.
- Store cool, dark and airtight.
- Fill jars full, so there is less air above the fat.
- Render in batches you will use, rather than one enormous jar opened repeatedly.
Rendered fat is the starting point for pemmican, which is the most calorie-dense shelf-stable food a household can make, and for soap and candles in the making and mending domain.