If you follow baking blogs or participate in online baking forums, you’ve probably heard this: The stiffer – lower hydration – the starter the sourer the taste. The thinking is that a stiffer starter promotes aerobic metabolism, thus creating more acetic acid, while a more liquid starter promotes anerobic metabolism which favors the creation of lactic acid. The difference is that acetic acid tastes more sour than lactic acid.
That’s all well and good. But as with so many things in making sourdough, there are several variables that can affect the sourness of your bread. For instance, with the loaf at the top, I used a 500% hydration starter to ferment the bread. It was 20% inoculation relative to the flour (BTW, I hate using that word with respect to bread because it has a specific scientific meaning). But at that hydration level, the yeast density was low, and it took 24 hours for final fermentation in my fridge. That loaf was nice and tart!
On the other hand, with the loaves immediately above, I used a 60% hydration starter, with the same inoculation level of 20%. But the yeast density was so much greater than the liquid starter, that final fermentation was barely 10 hours and I was pushing it, which accounts for the less open crumb. It hardly has any sour taste.
Myself, I’ve never bought into that rule of thumb that a stiffer starter will make a more a sour tasting loaf of bread. I’m quite familiar with the food science behind that and agree that aerobic metabolism promotes the production of acetic acid. But baking as long and as much I have, the best way I know to make a sour loaf is to have a long, cold final fermentation that favors bacterial over fungal activity, but also, making sure that my inoculation level is only about 12 to 13% to ensure I’m creating a less competitive environment that favors the bacteria in my dough.
You see, while yeast metabolizes, it creates inhibitors that block bacterial activity, effectively mitigating or eliminating competition. So, using a lower inoculation level will ensure a lower relative yeast density and will help mitigate fungal activity, and in turn, allow the bacteria to flourish during bulk fermentation. Then when bulk fermentation is complete, doing a cold fermentation of around 38℉ (and no higher than 40℉) will slow down yeast activity even further and let the bacteria continue do their thing. These principles apply to using all sorts of starters, from pure liquid fruit-based starters to high hydration starters, to super-stiff starters. So, at least for me, the type of starter isn’t as relevant as the dough fermentation techniques I employ.
That said, I could be completely full of it, and there are folks who will disagree with me vehemently. I get that. But for me, it’s time and technique that will dictate how sour my bread is, not my starter.