MWTC,
It’s hard to generalize on these matters because each starter has its own personality, or DNA, so to speak. However, there are some general activation methods that might help you get your starter in proper “working” condition. In your case, if you have been feeding your starter every three days, you should be in pretty good shape and should be able to get your starter in working condition pretty easily.
In your case, you should take your starter culture out of the refrigerator, remove a part of it, and feed it with flour and water. The amount of flour and water that you add to the starter will depend on what consistency of culture you desire to work with and the amount you want to use. Whatever hydration you decide to use, you should take note, preferably by weight, of the amount of flour and water added so that you can calculate its hydration. Ideally, over time, you want to use the same amounts of flour and water so that the hydration remains constant.
Some people make two versions of cultures, a liquid culture and a sponge culture, usually as a matter of preference or convenience or for use with different recipes. The difference is the amount of water. In Ed Wood’s book, Classic Sourdoughs, his liquid culture is 48% flour and 52% water, both by weight. His sponge culture is 65% flour and 35% water (also by weight). After feeding, each culture is proofed for 6 hours at 85 degrees F if a proofing box is used (you can use your MR-138 unit), or for 12 hours at a room temperature of 68-72 degrees F. This is the “working” culture. At the end of the relevant period, the working culture should be bubbling and foaming and expanding significantly in volume. In my experience, there is more bubbling and foaming with a loose starter culture than a stiff starter culture. Once fully activated, the working culture is combined with other ingredients to make the final dough, which is then subjected to its own fermentation regimen.
I haven"t worked up the numbers for your dough formulation but my recollection is that your first preferment stage is a “natural” poolish and your second preferment stage is a “natural” sponge (which I believe you have been referring to as a “biga”), with hydration similarities to the two cultures described by Ed Wood. If so, I believe you should be seeing some aspects of the behavior as discussed above, with at least some signs of bubbling and foaming and volume expansion. Usually people don’t combine cultures into multiple stages like you have been doing, or at least I haven’t seen or read anything to that effect, so I can’t say for sure what you should be seeing. But, if you haven’t been seeing the above signs, it is possible that your culture fermentation temperatures have been too low, or you haven’t given them enough fermentation time. Since you have a ThermoKool MR-138 unit, you might want to set it at 85 degrees F and see how long it takes for your starter (after feeding) to exhibit the characteristics mentioned above. You might be able to do this at both stages of your preferment, although I can only speculate as to how the second stage of your preferment will behave. Running the above test should give you the answer. This can be important since if your culture after the second stage is overfermented, it can have negative implications for the final product.
I assume that after you have used part of your starter culture to make your doughs you have been feeding the remaining portion with flour and water and returning the refreshed culture back to the refrigerator after a period of about an hour at room temperature. That is considered the proper way to treat the starter culture at this point.
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