Name: To, Make Yeast
Ingredients: 2 ounces of flour; 1 quart of water; coarse powdered marble; sulphuric acid (diluted with water)

To, Make Yeast

Ingredients

2 ounces of flour
1 quart of water
coarse powdered marble
sulphuric acid (diluted with water)

Directions

Prepare the flour jelly

Boil the flour in water until it reaches a thin jelly consistency.
Pour the flour jelly into the middle part of the yeast-making apparatus.

Make the gas and ferment

In the lower vessel, add coarse powdered marble and pour diluted sulphuric acid over it.
Adjust the apparatus and place the upper vessel nearly closed.
Allow the fixed air to pass through the valve and into the flour jelly for a few hours until it ferments.

Store the yeast

Remove the yeast from the machine and store it in a bottle for use.

Recipe from a historical cookbook (Internet Archive).

Transcribed from a scanned cookbook and modernised for today's kitchens. Where the book gave no heat or time, or said "a moderate oven", the temperatures and times here may be modern equivalents rather than the book's own figures.

Explore the science

What each ingredient does

Flour: Forms the thin jelly that the fixed air ferments, providing the material for the yeast to grow in.
Coarse powdered marble: Reacts with the acid to release the fixed air (carbon dioxide) that drives fermentation.
Sulphuric acid: Reacts with the powdered marble to produce the fixed air used in fermentation.

“What each ingredient does” and “The step that matters” were written by Claude from this recipe’s own method and reviewed in samples by CompKitchen.