I see many peoples' favourite bread Instagrammer is getting heavily and interestingly into pasta madre creation.
I have yet to dabble in the dark art, but I'm tempted...
And while we're on the topic, how's this for a big one?
I am absolutely confused by her comment that it's not sour at all.
Everything I've read suggests that these two factors:
- low hydration - 64.4F temp
should promote heterofermentative bacteria, meaning a mixture of acetic and lactic acids.
Why isn't is sour?
There is a lot of conflicting information about starters and sourness, but I would say the general consensus is that low hydrations favour sweet and high hydrations favour sour.
With regards to temperature, low temperatures for acetic, middle temperatures for yeast (sweet) and high temperatures for lactic. So 64.4F does seem a bit low, but I haven't yet read her posts on the subject fully, so I'm not sure of the context.
From my own experience, I've also found that the amount of whole grain flour you use in your starter makes a big difference to sourness. Even if you use only 20% WG flour you will be making a much more acidic starter than if you use 5% WG or all white BF.
I thought it was low hydrations favor sour while high hydrations flavor lactic/sweeter?
Like I said, there seem to be a lot of different views on this. Here's what Modernist Cuisine say on the subject:
"Additional factors, including hydration, also influence how a sourdough starter matures. Levain can vary in hydration. If you mix together equal parts water and flour, you’ll produce a levain that is fluid—that is, highly hydrated. We refer to this as a liquid levain (pictured on the right in the image below). If you add more flour to the mixture, say 120% flour to 100% water, the result will be stiff (left). In our experiments, we noticed perceptible differences in pH: the more liquid the starter, the more acidic it will be. (So if you like your sourdoughs good and sour, use a liquid levain.)"
But I'm sure you will be able to quote many sources that give the opposite view - such is the subject of breadmaking!
hmm. I will do the experiment myself and report back. You are referencing Modernist Bread, not Modernist Cuisine, right? I have Modernist Cuisine, but not bread.
"sour" and also "sweet" are subjective terms.
Sensory tests reveal acetic acid to be more pungent and more offensive but lactic acid while still sour it has rounded quality to it. Also acetic acid is volatile which means it gets up your nose but lactic doesn't have that quality.
I've avoided referring to the Italian SD starter as a "sweet starter" because I believe it to be a misnomer. Lactic acid in low doses is pleasantly "acidic" or "tart" and not sweet. I think some may say "sweet" to polarise something that is "acetic" sour.
Objectively acidity can be measured as pH and TTA and the ratio of acids is often referred to as fermentation quotient in scientific literature. It is generally accepted that low hydration starters shift the balance towards acetic acid however acids accumulate more slowly at lower hydrations.
Lance, low hydration will favor more acetic acid production as a percentage of acids by heterofermentative bacteria, which produce both acetic and lactic acids. Homofermentative bacteria produce only lactic acids. Temperature plays a role as well, warmer will end up producing more lactic acid.
Both acids will result in a lower pH. My original response should probably have been more specific, in that the conditions would seem to favor the acetic-acid flavor profile. Both types of acid in these breads, lactic and acetic, will be sour, we just tend to perceive one to be stronger than the other because it has a more pronounced flavor.
In re-reading her actual post in the link you provided, maybe the sugar-water soaking plays a role in this, or, perhaps her starter is like mine, in that it just doesn't have much of the acetic-acid producing bacteria (i.e. I have near lab-control environment capability, and I've tried just about everything to get mine to be more acetic, and it just doesn't do it, so I have a theory in that it all depends how you culture it at the start).