Using sponge method with bread machine.
It seems to me that bread-machine recipes, and the machines themselves, are designed around using 1 packet, (7 grams, or 2-1/4 teaspoons) of instant dry yeast. Or... anywhere from 2 to 3 teaspoons of yeast.
It occurred to me that if you want to save yeast, you might be able to make a sponge first, using perhaps 1/8 tsp yeast, and some water and flour, and maybe sugar, taking the water/flour out of the total recipe amount.
The flour/water/sugar would then grow or cultivate the 1/8 tsp yeast to an amount equivalent to the 2-1/4 tsp.
Then the sponge is added in to the rest of the recipe, (keeping total flour and water the same as original recipe) and in effect saves 2-1/8 tsp of yeast, per loaf.
Timing, temp, and type of flour would be critical.
Going from 1/8 to 2-1/4 is a factor of 17. So it's a 16x, or 1600% "increase." Or, doubling 4.09 times if I did the math right: log (base 2) of 17.
Has anyone done this? Are there any rules of thumb to use for estimating growth rates for IDY? (Currently looking at sourdough yeast rates.)
I found this: http://www.thefreshloaf.com/node/59477/sourdough-yeast-growth-rates-various-temperatures [1] Where the first graph is commercial yeast.
So, assuming a .3x _increase_ per hour (1.3 multiplication factor), at 21 C room temp, doing some math, it looks like 2.65 hours to double the yeast cells, and I would need to double 4 times, about 10.6 hours. Does anyone see any glaring errors in that logic or in the math?