In soap making, as in cooking, the fats and oils must be of quality. In fact fat will have an off smell to it. But just as the cooks of old added spices to mask ode of rancid, so too did the soapiers of old.
D.E. MacIntyre recounts in, Prairie Storekeeper.
"No matter whether the butter was good or bad the price was the same to everyone, for any woman would have been insulted if her butter was downgraded. And if I sold it, I was supposed to sell it at the same price I paid for it. Most of it was unsaleable and I packed this kind into butter tubs and shipped it off to soap factories in Winnipeg."