To make clean lamp fuel from raw fat, chop the trimmings small, melt them slowly in a pot with 2 cm of water at the bottom for 30 to 90 minutes, then strain through two or three layers of cloth and let the fat set so the water can be separated from it. Keep the heat low enough that the fat never smokes, and never put water on a burning pot of fat.
Part of Oil Lamp Construction
Raw fat trimmings become lamp fuel when they are melted slowly, strained and separated from their water. Rendering for food and soap is covered in Animal Fat Rendering.
Slow Heat And A Layer Of Water Stop The Fat Scorching
Scorched fat smokes and smells. A little water in the bottom of the pot keeps the temperature of the fat low while it melts, because the water holds the pot near its own boiling point until it has gone. Whiter fat makes cleaner fuel, so choose the white trimmings from butchering.
Method
Step 1: Chop. Collect fat trimmings from butchering and chop or grind them into small pieces. Smaller pieces render faster.
Step 2: Melt. Put the pieces in a heavy pot with 2 cm of water in the bottom. Heat on low and stir occasionally. The overview says never to let it boil; read that as no rolling boil and, above all, no smoke. The water simmers off first; bubbling then quietens when it has gone, which is the sign the fat itself is clear.
Step 3: Finish. Remove from the heat when all the solid pieces have melted and only crispy bits remain. The overview gives 30 to 90 minutes. The crispy bits (cracklings) are edible.
Step 4: Strain. Pour through 2 or 3 layers of cloth into a clean container.
Step 5: Settle. Let it cool. Water settles to the bottom and the clean fat solidifies on top.
Step 6: Separate and repeat. Lift off the fat disk and scrape any gunk off its underside. For the cleanest fuel, re-melt and strain again.
Worked Example
The overview says a deer’s fat trimmings, roughly 2 to 3 kg, give enough lamp fuel for 60 to 100 hours. At the overview’s rate of about 25 ml/h for tallow, 60 h × 25 ml/h = 1,500 ml and 100 h × 25 ml/h = 2,500 ml, so the claim is 1.5 to 2.5 litres of fuel. The overview does not state a yield per kilogram, so weigh and measure your own batch before planning around it.
Common Mistakes
- Letting it smoke. Smoking fat is overheated. Take it off the heat; scorched fat smells and sooty lamps follow.
- Skipping the settle step. Water left in the fat makes the lamp spit.
- Pouring still-hot fat into a plastic or thin container. Use a container that tolerates hot fat.
Safety
Hot fat burns skin and burns as fuel
A pot of hot fat that ignites must be smothered: slide a lid over it and take it off the heat. Never pour water on burning fat. Water goes under the fat, boils explosively and throws burning fat out of the pot. Do not leave a rendering pot unattended; do not carry it while it is very hot. Render in a ventilated place or outdoors; rendering fumes and any smoke are an irritant and incomplete burning of fuel under the pot makes carbon monoxide. For burns, see Thermal Injury Care.
What’s Next
- Learn next: Animal Fat (Tallow & Lard) — what to expect from the finished fuel
- Combine with: Fat Preservation — storing rendered fat so it stays usable