Homemade Yeast
I have been thinking a lot about this recipe and the bread I have made from past batches.. It is refered to as a barm, which is also a yeast rich foam that has risen to the surface of home made beer. In the beer the hops are used not only for flavour, but for their preservative attributes. This slows the bacteria growth. In bread this would keep the dough from getting too much of a sour flavour. Because of this, any bread made with this starter will have an undertone flavour from the hops instead of a sour flavour from a water/flour starter.

After all that thinking - what a waste of time - Elizabeth David says it succinctly and with a nice historical florish on page 101 of English Bread and Yeast Cookery.
Hops were usually included, more as a preservative, or preventative of sourness, than as a stimulant.....Until well on into the twentieth century and even after the First World War, there were still a few bakers making their bread with barm rather than with compressed distillery yeast; people accustomed to bread leavened with barm held that its flavour was much more interesting than that produced by modern yeast. It is one of those lost tastes.

Well, perhaps it can be revived. I will post a bread recipe using this barm next week, once my barm is done.

Spontaneous Barm

Ideally I try to use organic flour, and have found the barm successful using whole wheat flour. The whole wheat barm does not allow for a bright white interior to your finished loaf – this being a very desirable quality one hundred years ago – but with our love of whole grain loaves and variety flours, the whole wheat barm works very nicely.

Ingredients
2 quarts water
3/4 cups hops, loosely packed
1/4 cup brown sugar, packed
1/2 teaspoon salt
1/2 cup bread flour
12 oz. potatoes, cooked and mashed

Preparation

Day One:
Combine hops and water and bring to a boil. Simmer for 30 minutes, stirring occasionally. Cool to lukewarm. Strain out hops, discard flowers. Place liquid in a 4 quart container. Stir in sugar and salt. Add some of the broth to the flour in a bowl to make a slurry. Add the slurry back into the hops broth, stirring well. Set the bowl in a warm spot, stirring occasionally, for two days.

Day Two:
Continue to stir the broth occasionally.

Day Three:
Stir in the still warm, (but not hot!), mashed potatoes. Stir well.

Day Four:
The mixture should have started to ferment. Let sit until the evening, then strain and store in bottles filled ¾ full of the yeasty coloured broth. Store in the refrigerator until needed. Bring the yeast to room temperature before using.

Barm will keep 6 to 8 weeks.
Note: I store the liquid in thoroughly washed and dried milk bottles. You can seal them using the old lids, (washed well of course), or cork, or even just plastic wrap with an elastic band to keep it secure.