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Potato Yeast
Cook and mash ten peeled potatoes. Pour on one quart boiling water, stir well together, add one coffee-cup of sugar, let it stand a few minutes; pour on a scant quart cold water, stir in one pint yeast or four well dissolved yeast cakes, and set it in a moderately warm place to rise. When well fermented, put into a stone jug, cork very tightly. One cup will make one large loaf of bread or two small ones. Keep in a cool place.
This is a bread starter rather than a dish: a potato-and-sugar medium that multiplies a small amount of purchased yeast into a keeping supply of liquid leaven. A few of its instructions need adjusting for modern yeast and modern containers.
- Do not cork it tightlyAn actively fermenting starter produces a great deal of carbon dioxide, and a tightly corked stone jug or a screw-top bottle can build enough pressure to burst. Use a jar with the lid resting on loosely, or a cloth and rubber band.
- Watch the temperature before adding yeastThe boiling quart plus the mashed potatoes will be far too hot to pitch into. The scant quart of cold water is there to bring it down; check that the mixture is at or below about 100F before the yeast goes in, or you will kill it.
- Yeast cakes"Yeast cake" could mean either commercial compressed fresh yeast (the modern cake is about 0.6 oz) or a dried yeast cake of the older sort, and the recipe does not say which. If read as compressed yeast, four cakes is a large pitch by modern standards; about 2 tablespoons of active dry yeast is a reasonable equivalent, and less will still work given the amount of sugar and starch on offer.
- Coffee-cup of sugarRead this as a standard cup, around 7 oz. It is food for the yeast, not sweetening for the bread, and most of it will be consumed during fermentation.
- PotatoesTen peeled potatoes means ten medium boiling potatoes, roughly 3 lb. Mash them smooth; lumps tend to settle out at the bottom of the jug.
- \Around 75-80F, warm enough to be brisk but not hot. It should be foaming and smelling actively yeasty within 6 to 12 hours; go longer and it turns sour and thin.
- Storage and lifeRefrigerate once fermentation slows. It will keep perhaps a week or two, separating as it stands, and should be stirred or shaken before use. Discard it if it smells of nail polish, cheese or anything putrid rather than of beer and bread.
- Using itOne cup replaces the yeast in a large loaf, but it is also about 8 fl oz of liquid and some starch. Subtract that much water from your dough and expect a slower, more sour rise than packaged yeast gives.
- YieldThe liquid alone comes to about two and a half quarts before the potato mash is counted, so expect roughly three quarts, enough leaven for a dozen or so large loaves if used promptly.
Before packaged yeast could be relied on, a bread-making household had to keep its own leaven alive, and potato yeast was one of the standard ways to do it: cooked potato supplies both starch and nutrients for the yeast, sugar drives a fast multiplication, and the result keeps in a cool cellar for days rather than hours. Recipes of this kind fill American cookbooks through the nineteenth century, often set beside instructions for hop yeast and salt-rising bread. The recipe offers "four well dissolved yeast cakes" as an alternative to "one pint yeast" -- a bought starting dose in place of a begged one -- though "yeast cake" at this date could mean either commercial compressed yeast, sold in the United States from the later nineteenth century, or a dried yeast cake of the older homemade sort, so the phrase does not by itself date the version. That the book still explains how to stretch four cakes into a jugful of liquid yeast at least suggests fresh yeast was not something to be bought every baking day.