Subject: 8. How do I stop my sourdough bread from flattening?
A very important aspect of making sourdough is the amount of starter used in the recipe and how long it has been since the starter matured. Typically, about 20-40% of the total flour should come from the starter. The higher the percentage of starter, the less proofing time it will stand. In other words, if 40% of the flour comes from starter, you may only be able to proof 3-4 hours before the loaves flatten excessively, depending on the starter and degree of maturity. I've never used Carl's starter, but since people like it I assume it has fairly low levels of enzymes which make it more tolerant to various baking procedures. Different lactobacilli have different capacities to degrade flour and to make acid and therefore they act differently in bread.
The standard methods to keep bread from flattening excessively include reducing water, increasing kneading or adding ascorbic acid (100-200 mg per 5 pounds of flour), making sure the starter is not overly mature, and doing some of the fermentation as a "bulk" fermentation. Bulk fermentation simply means that after mixing the dough you let it sit for 2-3 hours at proofing temperature before shaping the loaves. That will give the bacteria/yeast time to make flavor and gas without having to worry about the loaves flattening. Then the loaves are shaped and a final proof of 3-4 hours results in a fantastic loaf with a more interesting internal and external texture.
One other important reason why sourdough loaves may flatten is that the starter is not fresh enough. When you feed your starter use the smallest amount of old starter that you can while still getting a very active ferment by the time you need to mix your dough. If the old starter is very active I would use only 5-10% by weight as an innoculum. Starters that are not fresh produce extremely slack doughs. The type of flour you use will help, but will not completely overcome the problem. If 20-30% of the flour in your dough comes from starter you should be able to proof a free standing loaf for many hours without flattening. I typically mix a dough, let it sit for 3 hours, shape into loaves, and give up to 5 hours of final proof with little flattening.
Water content for this type of loaf is 56-60% on flour.
While flattening can occur from hydration (particularly with baguettes) it mainly has to do with the fermentation and proof. Dough that is over-proofed will collapse on itself when you try to slash it or, in some extreme cases, if you even touch it. The reason for this is because the gluten has been broken down by the bacteria and yeast that it can no longer support the structure of the bread. Bread that is over proofed will also be really sour. While some people like sour bread, it will generally be at a detriment to your big, holey, irregular crumb. This can also happen with your starter. A well proofed starter will have doubled (atleast) in volume, be full of bubbles and will just be starting to collapse on itself, but if you reached in a pulled some of it out, it will still have thick strands of gluten keeping it elastic and extensible. If it is proofed for too long, the gluten will break down and you will eventually have a soupy mass that won't stretch at all because it will be a liquid. If a loaf is proofed too long, it will start to collapse when you try to slash it or when you transfer it to a peel. Hydration can be as high as 85% and while you won't be able to shape it, you will be able to get really big holes without it flattening on you even though the dough will seem flat before you bake it, it will puff up in the oven.
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