It doesn't get much simpler. The following formula expressed as baker's percents is used to refresh existing sourdough starter:
67% all purpose flour
33% cake flour
The above combination of flours is approximately 9.6% protein. A 50:50 mix of all purpose and pastry flour is a close alternative, as are several other flour combinations.
Calculate ingredient weights with a particular flour weight
For refreshing existing sourdough starter using a half-gallon sourdough pot, 300 to 500 g for the flour weight may be used, depending on how much is needed to fill the pot. You may use 400 g for the flour weight, which is enough for about 7 large pancakes. Multiply the flour weight times each baker's percent:
268 g all purpose flour = 400 g x 67%
132 g cake flour = 400 g x 33%
640 g water = 400 g x 160%
Refreshment ratios are not very important for pancake dough, perhaps other than something greater than 50:50. The objective is to fill the nearly-empty sourdough pot with new dough and mix well with the old dough.
Once refreshed, the entire sourdough pot is incubated in a water bath at 88-90°F to favor lactobacilli. A digital stick thermometer is an indispensable kitchen tool.
The water level is about the same as the dough in the sourdough pot. This water bath technique warms the dough quickly.
When a thin, foamy layer first develops on top of the starter, it is ready to make pancakes or refrigerate.
Weighing batter & making two large pancakes
300 g starter (1 1/4 cups)
1 g salt (1/8 tsp)
1.5 g baking soda (1/4 tsp)
Using a 2-cup glass measuring cup, weigh or measure out starter and other ingredients, whip thoroughly and quickly, and immediately pour batter into small squirts of oil in the middle of two large and preheated cast iron pans.
Notes about incubation and storage
Between uses, store the starter in the refrigerator, it will keep for about a month until it must be refreshed. Incubation is only done after a refreshment. It is not necessary to incubate every time pancakes are desired, only when the sourdough pot is near empty.
Depending on how long it's been since the sourdough was last refreshed, it usually takes from 1 to 3 hours of incubation. If it's only been a few days since the last refreshment, it takes less time: if it's been nearly a month, it takes longer. How long it takes also depends on the refreshment ratio. With relatively more new dough, incubation takes longer: with relatively less, it goes faster.
When a thin layer of bubbles or foam first develops on top, the starter is ready to make pancakes, or refrigerate. At this point it is still a young culture, it could be incubated for longer, but storing in the fridge at this early point of growth seems to increase storage time.
Record the date of the most recent refreshment on a paper label stuck to the lid of the sourdough pot. Sometimes it gets forgotten in the back of the fridge, and it's useful to know its age!
Yeasts versus lactobacilli
Sourdough for pancakes is a bit different from sourdough for bread. There are two different kinds of organisms in sourdough, yeasts and lactic acid bacteria. For making bread, you want to favor the yeasts, which make carbon dioxide. For making pancakes, you want to favor lactobacilli, which makes mostly lactic acid.
When making bread, it is the yeast which makes the carbon dioxide which slowly leavens the dough. When making pancakes, the carbon dioxide is created when you add baking soda which combines with the acids, that reaction accelerates when the batter is warmed by the hot pan.
In general, it's much easier to make lactic acid, the starter doesn't require anywhere near as much care. It is more difficult to evoke good yeast growth for making bread.
When you're making sourdough starter for bread, you are trying to optimize yeast growth, traditionally with 3 refreshments before incorporation into bread dough, and you do that at room temperature or optimally at 75-80°F.
Making sourdough for pancakes is much simpler, all that's needed are the acids. A single refreshment followed by a short incubation at about 89°F is all that's needed.
Calculation of flour weight for any size sourdough pot
To know what flour weight to use to fill up your sourdough pot with new dough, this will get you very close to a full pot no matter how much starter or old dough remains. First you need a few data points or variables:
Formula % = 260% (100% flour + 160% water, the sum of the baker's percents)
Weight of your sourdough pot when empty ⟶ SD pot empty
Weight of only cool water when your empty sourdough pot is filled to desired fill line with water ⟶ Max capacity
Weight of the sourdough pot with a little starter remaining ⟶ Old dough with pot
Old dough with pot − SD pot empty = Old dough weight
Max capacity − Old dough weight = New dough weight
New dough weight ÷ Formula % = Flour weight.
Once you have the flour weight, use baker's percents to calculate the refreshment weights for flours and water to fill your sourdough pot.
Revised on February 23, 2018.