Notes collected by Orlando de Medici for the Peasants of Carolingia, 31-Mar-01.
Having received basic information on the rendering of tallow, I wanted to give it a try. I have heard that tallow is best made from suet, and that the cleanness of the source fat is quite important, as any protein matter will make the resulting tallow not keep well. Also, I suspect that the unpleasant odor, smoking, and/or sputtering of tallow candles reported by some people may be due to unclean or water-bearing tallow. To avoid such problems, I planned to clean and dry the tallow carefully.
I bought 8.52 pounds of suet (@ $0.89/lb) from the local supermarket. It came in seven blocks. Having heard that the rendering process works fastest with the best yield when the suet is in small pieces, I first attempted to coarsely grate the suet. This proceeded far too slowly for my taste, so I instead cut it into thin strips. I found that a hand knife would soon be coated with fat, making it slippery, and that force required would hurt the hand pressing on a small knife. A rocking cleaver (as used for mincing herbs) worked best. I aimed for minimal cuts off the end, accepting up to 1/4 inch in thickness.
I have heard that the simmering process can take a day or two, but I wanted to see if I could achieve a quicker rendering using a pressure cooker. There was too much suet to do the work in one batch, so I placed half of it in the pressure cooker, and added just enough water to bring it level.
I 'cooked' the suet for four hours, with the pressure valve gently rocking. After this time, I cooled down the cooker, and poured it out through a strainer. I was pleasantly surprised to see that very little solid material remained, indicating a good yield. I put the liquid in the refrigerator to cool, and filled the cooker with the other half of the suet and the solids from the first batch, and started it up again. This mixture was also on the stove for four hours. I strained the solids out, which weighed about 4.5 ounces, and refrigerated the liquid. This liquid seemed considerably darker than the previous batch. I suspect I set the heat too high on the second batch, causing the water to evaporate, and the tallow to boil. We'll see if it comes out clean, or at least can be cleaned afterward.
I removed the first batch from the refrigerator, separated the solid white tallow from the yellow-brown liquid. To clean it, I put the tallow in a pot with water and melted it, then returned it to the refrigerator. I repeated the cleaning process several times for both halves, sometimes skimming the scum that arose when melting the tallow, sometimes scraping the tallow block gently with a knife. The second half cleaned up nicely.
In summary: rendering fat is not difficult. I did not find the quality of the source material to be as important as I was told, though lower-grade material will mean you lose more fat when you scrape it to get rid of the protein matter. I find the best way to judge the process is by the amount of remaining material, and set the time and method of rendering based on that. Cleaning is very important, and can be achieved by letting the fat cool until it is solid, separating it from the dirty water, scraping the fat if necessary, and remelting/recooling the fat as needed.