The full flavor of barm will not develop until it has been refreshed until it has been refreshed 2 or 3 times over a 2-week period, during which time the organisms native to your region will gradually take charge of it.
3 1/2 cups unbleached bread flour
2 cups water, at room temperature
1 cup seed culture
- Stir together the flour, water, and seed culture in a mixing bowl (you can discard the remaining seed culture or give it to a friend).Make sure the seed culture is evenly distributed and all the flour is hydrated. It will make a wet, sticky sponge similar to a poolish.
- Transfer this sponge to a clean plastic, glass, or ceramic storage container twice as large as the barm. Cover the container with a lid or plastic wrap and ferment at room temperature for approximately 6 hours, or until the barm is bubbly.
- The plastic will swell like a balloon, as will a plastic lid. When this happens, open the lid to release the gas (try not to breathe it as it escapes – the carbonic gas mixed with ethanol fumes will knock you across the room!).
- Replace the cover and refrigerate overnight before using.
- The barm will be ready to use the next day and will remain potent for 3 days. After that, or if you use more than half during the next 3 days, you will need to refresh it as described below.
Refreshing the Barm
- The standard refreshment for barm is to double it at least. However, you can also quadruple it, as the organism in the barm is capable of feeding on a large refreshment and converting it into starter. I double the barm at each feeding if I want a very sour bread, but I triple or quadruple it when I want a less sour flavor.
- It is important to understand what happens when you refresh the barm. After 4 to 7 day, the acids and protease enzymes in a barm that has not been refreshed break down the gluten, turning what was at first a strong, stringy sponge into a protein-weak, potato-soup-like consistency. That’s why, refresh your barm 3 days or less before you plan to use it (ideally, the day before). If you have a lot of barm but haven’t fed it for a while, discard all but 1 cup and refresh it with 4 cups of flour and 2 ½ to 3 cups water, stirring until all the flour is hydrated.
- If you have been using and feeding your barm regularly, you do not necessarily have to discard any. However, what you do not wasn’t to do is, for example, use 1 cup of barm from your supply to make some bread, then refresh the remaining barm with only 1 cup flour and some water. You must always at least double the remaining barm.
- If you want to save the barm but do not plan to make bread for a while, you can refrigerate it for at least 2 months in an airtight container, and then refresh it by discarding all but 1 cup and building up from there. Or, you can freeze the barm for up to 6 months and then defrost it in the refrigerator 3 days before you need it. When it has thawed enough to use (the next day), discard all but ½ cup and refresh as described. Then refresh again the next day you will have to about 4 to 6 cups barm. Since you do not want to freeze a glass or ceramic container, you should transfer the barm to a zippered freezer bag that has been misted with spray oil (allow enough room for expansion and gas development).
- Use high-gluten flour for the refreshment (except in the case of a rye barm), as it has more gluten than in bread flour to withstand the acid and enzymatic degradation.
- You can refresh in two ways. One is to weigh the amount of barm you plan to refresh and the other is to eyeball it.
- The weighing method is simple. Weigh the barm and calculate how much flour and water it will take to double, triple, or quadruple the weight (the easiest way is to figure equal parts water and flour). The larger the refreshment, the longer the fermentation time, usually 4 to 6 hours, depending on the size of the refreshment and how cold the barm was when you started.
- When the starter is bubbly and foamy, put it in the refrigerator overnight before using it. Technically, you could begin using it as soon as it foams up, but I wait for the overnight development, because it gives the bread more complexity of flavor.
Source: The Bread Baker’s Apprentice by Peter Reinhart