Barm in place of Levain? Confused....

There are no exact definitions for any of these terms.  In fact, within the next 24 hours, in this very thread, you will receive 10 "definitive and correct" definitions for each/all of the terms... and there will be 10! (10 * 9 * 8 * 7...) differences among them ;-)

With that in mind...

Starter, levain, and stiff levain all refer to sourdough cultures of one form or another.  Sourdough cultures being self-perpetuating yeast/bacteria ecologies that live in a handy mix of flour & water in a jar on your counter or in your refrigerator.  The yeasts provide dough lift and food for the bacteria; the bacteria provide an acidic living environment for those types of yeast and those acids provide other benefits in nutrition, keeping, and taste.  Also known as "natural" or "wild" yeast.

Stiff levain is a sourdough culture with a lower proportion of water to flour by weight.  I keep my primary culture at 90 grams flour to 60 grams water; that is generally considered stiff.  Many people keep their cultures at 100%, say 75 g flour to 75 g water.  Depends on what type of culture you want and how you manage it.

"Barm" has specific meanings, but unfortunately Peter Reinhart redefined it in 2 of his earlier books and created utter confusion.  Best to avoid that word except in the context of a specific recipe.

Poolish, biga, and pate fermente are all examples of "pre-ferments" made with bakers yeast.  Recipes made with only bakers yeast are known as "straight doughs".  Recipes with pre-ferments direct you to mix a portion of the flour and water and a tiny bit of yeast and leave them to develop for 8-24 hours before mixing them into the dough.

There are, again, no definitions enforced by Interpol, but in general:

Poolish is a larger proportion of the total recipe, is more liquid, and uses more yeast (say 150 g flour / 238 g water / 1/8 tsp yeast)

Biga is a smaller proportion of the recipe, is less liquid (you already figured out that is therefore 'stiffer'), and uses only a very small amount of yeast (1/32 tsp)

Pate fermente is pinched off from today's dough after the first or second rise, wrapped, and put in the refrigerator to add to tomorrow's (or next week's) dough.

Hope that helps.

sPh

I'm almost afraid to answer your question, because some expert will correct the nuances of my ignorance. That said, here's my basic understanding.

Barm, starter, levain are essentially the same thing: muture, stable populations of yeast and lactobacteria, living together in harmony;i.e., sourdough

Poolish and biga are flour, water, and a small of amount of commercial yeast mixed twelve to sixteen hours before mixing the final dough. They provide added flavor and leavening to the final dough, but most bread formulae made with poolish or biga, add further commercial yeast to the final dough. biga (Italian) are usually stiffer than poolish (introduced into French baking, by Polish bakers, thus poolish.).

pate fermente is old dough. A piece of dough from yesterday's baking, that provides the leavening for today's bake. A small portion of today's bake will be saved overnight, and, abracadabra, tomorrow its pate fermente.

Stiff levain is levain with with less water (hydration 50%-60%) than usual levain.

For the most part, they are interchangeable in bread formula, but minor adjustments need be made to keep the final dough consistant in mass, hydtration, and leavening power.

A lot of sourdough terminology is a semantic labyrinth.

David G.

P.S. I should also say that  the flavor profile of any bread will be influenced slightly by whatever adjustments you make.

First off, you have two categories of  leavening: sourdough and commercial yeast.

In the sourdough camp, we pull from your list:

Barm, Starter, Levain and Stiff Levain.

They are, in effect, all the same, built from wild yeast but some people just call them by different names. Stiff levain is, specifically, a stiff version of a wetter levain. More like a dough compared to a liquid version. You could just a easily have stiff barm or stiff starter. "Stiff" merely specifies the hydration levels. Levain is the french word for sourdough starter. Barm is... well, it's an odd word for starter. Although I've seen it refer to a specific type of build, still made with wild yeast. Generally, however, the three words are interchangeable.

Meanwhile, Poolish, Biga and Pâte Fermentée are all pre-ferments, meaning an amount of dough built ahead of time and allowed to develop over a longer period of time to add flavour and other qualities to a newer dough. Each one has it's own sort of formulation and are usually going to be made using commercial yeast. Any good bread book that asks for these will also explain how the author wants it built. I don't own Local Breads but I would expect Lepard's recipe for Poolish, etc, is in there.

As for your question regarding having to make a new levain/starter when you already have one, there's no point. If yours is active and dependable, use it.

All you'd likely need to assure is that the hydration used in the recipe matches the hydration of your own starter. If it doesn't - say your is 100%, they want 66% - then it's merely a matter of taking some of yours and building up a stiffer or wetter version for that recipe.

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heheh.. There were no replies when I started writing this response and there were several when I finally got around to posting it. Glad to see that everyone seems to be in general agreement on these points, not too much discrepancy on the answers.