Pare half a dozen middle-sized potatoes, and boil them in a quart of soft water, mixed with a handful of hops, till quite soft. Then mash the potatoes smooth, not leaving in a single lump. Mix with them a handful of wheat flour. Set a sieve over the pan in which you have the flour and mashed potatoes, and strain into them the hop-water in which they were boiled. Then stir the mixture very hard, and afterwards pass it through a cullender to clear it of lumps. Let it stand till it is nearly cold. Then stir in four table-spoonfuls of strong yeast, and let it stand to ferment. When the foam has sunk down in the middle, (which will not be for several hours,) it is done working. Then put it into a stone jug and cork it. Set it in a cool place.
This yeast will be found extremely good for raising homemade bread.
Yeast when it becomes sour may be made fit to use by stirring into it a little sal-eratus, or pearl-ash, allowing a small tea-spoonful to a pint of yeast. This will remove the acidity, and improve the bread in lightness. The pearl-ash must be previously melted in a little lukewarm water.