Myth Alert--Refrigeration

You'll read and hear opinions that the way to increase the sourness of sourdough bread is to refrigerate the dough for extended periods. This is false.

The sourness of sourdough comes primarily from lactobacilli. Sourdough lactobacilli are related to the cultures that turn milk into yogurt.

The ones that live in sourdough cultures, like the yogurt ones, are active in warm environments and inactive in cold ones. Your bread dough will not become more sour in the refrigerator. What happens in the refrigerator is that both the yeast and the bacteria slow down a lot. With prolonged refrigeration, they eventually consume the sugars in the dough and go dormant. What you get then is ugly bread with a pale crust, because the sugars that brown during baking are gone.

Lactobacilli and yeasts have slightly different ideal temperatures. The best compromise seems to be about 85 degrees F (29.5 C). With higher temperatures, up to around 92 F, you may get more souring, but you'll quickly lose your yeast, and with it, the rising capacity of the bread. With slightly lower temperatures, you'll get more yeast activity, but less souring.

But the refrigerator doesn't do sourdough bread any favors, even if a lot of books and web sites say it does.