When feeding your barm it's necessary to double it at least. Normally, half would be taken to make a sourdough loaf, the other half built back up to a resting barm. If you know you're going to be making several loaves you can quadruple the barm in preparation. There will still be enough organisms in the barm to handle the large feeding and conversion to a starter.

By doubling the barm you get a more sour bread, triple or quadruple you get a less sour bread so it depends on your tastes. The bacteria does not work as fast as the yeast so if you more than double the barm the yeast will bounce back faster than the bacteria making a stronger less acidic leavening sponge. On the second or third day after feeding the bacteria catches up giving it the more distinctive sour taste. When you use a fed barm depends on your personal tastes. By the fourth day it is too sour and should either be fed again or stored for later use. You can freeze it if you know it's going to be months and months before you bake again but it would be better to put it on a regular feeding schedule once every 2 months or as often as you wish to bake the bread. If you freeze it, you'll need to feed it several times before you can use it again.

After the fourth day from a feeding the acids and enzymes break down the gluten, turning the strong, stringy sponge into a protein weak soupy consistency. There are still lots of organisms to flavor the bread but the leavening power will be considerably less. One to three days before you plan on baking sourdough bread your barm will need to be fed.

Use the highest gluten content flour you can find for all feedings of your barm to stand up to the acid and enzymatic actions.

To do a regular feeding, weigh the barm to calculate how much flour and water it will take to double, triple or quadruple the total weight. If you have one pound of barm you can build it to double weight by adding 8 ounces of flour and one cup of water (50:50). The larger the feeding the longer the fermentation time, usually 4 to 6 hours at 65 to 75 degrees. After fermentation the starter barm will be bubbly and foamy, store it in the refrigeration overnight before using. You can use it right away but there will be less flavor to the bread.

If you have not fed your barm for a long time discard all but one cup of the barm and feed it with four cups of flour and 2 1/2 to 3 cups of water and stirring until all the flour is hydrated.