I have been working with recipes from the book "Gluten Free on a Shoestring Bakes Bread" and all of the breads have an acrid, bitter under-taste to them. It's very unpleasant. I searched for what might be causing this and the internet says it's a matter of too much yeast. How much is too much? The recipe in front of me right now calls for 2 1/3 tsp instant yeast to 3.75 cups (500g) of flour.
I have experienced this too with some gluten free foods and have yet to discover the problem. That much yeast shouldn't be a problem with that much flour. At least i think it shouldn't!
Do the recipes you use also call for baking soda? I know that is baking soda is not paired with enough of an acid it produces a bitter taste.
I have found that both sorghum and millet flour can develop a rancid bitterness even if the package "use by" date is still a year out. The resulting bread I made initially had an ok taste that became almost unbearably bitter as I chewed.By the time I should swallow, I just spit it out. It might be that these flours should be held at refrig or freezer temps in order to stay fresh. I didn't have the problem when I made my GF breads from other flours. It's not the yeast.
For these recipes, I am using the flour blend designated in the book.There is no sorghum or millet. I have experienced rancid millet and I know the bitter flavor you mean, but it isn't that. When I use less yeast and less salt and less sugar, the breads do taste better. Since neither salt nor sugar would cause this acridness, Ithink it is probably the yeast.
These breads need long fermentation in the fridge, typically 12 hours or more. If you ferment a GF bread for 4 hours at room temp it will smell like feet and taste like cheese.
Gluten-free baking really doesn't work the same as regular baking.
I've dabbled in GF but I feel the flours and doughs share a lot of the same characteristics as rye flour. Laura T and Samantha are 2 members that have done extensive research and baking to develop fabulous GF breads. Do a search and find a few threads. Since this forum (Baking for Special Needs) is not that old, just scanning posts from last year would be productive.
Please keep posting your experiences and questions. Wheat free and GF baking are but an extension of baking and very interesting.