The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

The Science of Sourdough: How Microbes Enabled a Pandemic Pastime

cyber's picture

The Science of Sourdough: How Microbes Enabled a Pandemic Pastime

Scientists peer into those jars on the kitchen counter to find out how what’s really happening

Mini Oven's picture
Mini Oven

:) There is more than one juicy tidbit in there!   

DanAyo's picture

This paragraph was copied from the linked article. The highlighted text is a shocker. Where is daBrownMan?

” Temperature matters, too. Lactic acid bacteria do best in relatively warm conditions, for example, so fermenting in a warm kitchen makes for a sourer dough, while cooler conditions lead to more of the fruity flavors produced by the yeast. Moreover, lactic acid bacteria, despite what you’d think, aren’t fond of highly acid environments. Home bakers who leave an acidic starter in a cold fridge for weeks between bakings can find they end up with a blander bread that lacks the distinctive tang contributed by the bacteria. (Pro tip: If you’re going to leave your starter in the fridge for longer than a week, make sure to refrigerate it immediately after adding fresh flour, when it’s least acidic. That, says Lacaze, will help the lactic acid bacteria survive the prolonged cold to acidify the rising dough.)

Edo Bread's picture
Edo Bread

Which as with so many things in bread, is in direct contrast to this tidbit from King Arthur Baking:

What makes the sour in sourdough bread? It's a combination of lactic and acetic acids, created as the dough rises and ferments. Refrigerating the dough encourages the production of more acetic than lactic acid; and acetic acid is much the tangier of the two. Thus, sourdough bread that's refrigerated before baking will have a more assertive sour flavor.

mwilson's picture

I agree with the highlighted text.

Fridge cold = stasis. Things do happen but under these conditions microbes will focus on survival and drift off into dormancy. That is why we use refrigerators, to slow microbial growth to help prevent the spoilage of food.

Once a low pH <3.8-4.0 is reached most SD associated lactobacillus will no longer grow. If they are not growing then their cell numbers will gradually decline. Even at fridge temps it doesn't take long for the pH to drop to this critical point.

Prolonged storage is a good way to make a starter more acidic but not a good way to help the microbes thrive.

Using a long-time stored starter that has become very acidic to seed a dough may push the starting pH so low that any surviving LAB can't work for long before shutting down again, and this low pH will also block native flour enzymes, hence the lack of flavour. I can recall Abe reporting this phenomena.

LAB can be expected to work best at pH 5-5.5 which also happens to be the optimum for for alpha-amylase.

Notice at 20hrs LAB start to decline while yeast remain stationary.

SirSaccCer's picture

To me it looks like there are a couple of things going on here. "Leav[ing] an acidic starter in a cold fridge for weeks between baking" isn't the same thing as refrigerating a shaped loaf overnight. When you leave starter in the fridge for weeks without feeding it, all kinds of unfriendly chemistry happens, which might kill off your bacteria. I'm not sure what it means to say that lactic acid bacteria grow best at warm temperatures--many bacteria grow faster at 37 °C than they do at room temperature. But it might be the case that, in the fridge, LAB is more active than yeast, leading to a relatively sour flavor in the proofed loaf. Whereas, if left for a long time at room temperature, the loaf is overproofed or goop by the time it really gets sour.

mwilson's picture
"Baker’s yeast, for example, can’t use the sugar maltose, which is therefore available for the lactic acid bacteria"

The above is obviously not correct. A misstated interpretation presumably.