May 28, 2019 - 9:24am
Reasons for starter % amount in the pre-ferment
A survey of sourdough recipes yields a wide variety of culture (starter) percents in the pre-ferment. Some have a smaller baker's percent and some larger. Hamelman, for instance, typically has a 20% BP for white starters and a 5% BP for rye starters. Also, recipes vary a lot in the BP of the pre-ferment to total flour so that may also be a parameter. I can understand that adjusting the starter % of the pre-ferment can accommodate for timing factors, but are there other reasons for the percent of starter in the pre-ferment?
Share
Steve, another big reason to reduce the percentage of pre-ferments is to slow the duration of fermentation in order to develop more flavor.
Dan,
Yes, that's the common idea, but it's still unclear to me why the amount of starter makes the difference. For instance, with less starter, the population density of the leavening organisms is smaller but looked at locally within the dough it seems the same thing is going on that would be happening with a higher density of organisms, just at a different rate. So with less starter, it would take longer to grow the leavening organisms to a level good for rising the dough but flavor wise I don't see the difference, Now, when the pre-ferment is retarded at a lower temperature, that makes sense because that promotes hetero-fermentation that contributes to the formation of acetic acid.
There are no timing factors - at least, none that are distinct from population-density and temperature factors. Time, temperature, and population-density all interact at all times; changing one of them changes the others too. Getting all of them near their ideal levels, either all the time or only once at the right moment, is the trick. And "population-density" is probably too narrow a term, because the byproducts of that population are also significant - density yes, but also stage of development. Plus in fact it's not a monolithic population but a compound/concurrent population that can change its internal proportions.
What I meant by timing was to fit one's schedule. If a quicker ferment of the pre-ferment is needed, then increasing the percentage of starter will create (percentage wise) the byproducts of fermentation quicker. But, yes, time and population-density are essential components as well. If a stiff starter is used with the same baker's percent it should have a higher population-density than a looser starter (given it has a higher percentage of flour in it).
As I was thinking some more about this issue, I also wondered if using a smaller percentage of starter and a longer ferment also allowed for more enzymic activity to occur that might or might not be related to the fermentation but could contribute to the flavor profile.
Another advantage I can think of for less starter and longer ferment could be that the extra time gives the whole grains and especially the bran longer to soften up. Kind of like a combination pre-ferment and soaker. Lately I've been experimenting with a pre-ferment where I put all the whole wheat in the pre-ferment (30-40% of overall flour) and a starter inoculation of 5-10% BP with an overnight ferment at room temperature. I think I'm getting more oven spring and open crumb but I need to do some more comparisons.
Absolutely, of course you're right about the schedule - time does indeed exist ? - it's just that all the other factors change too, as soon as you change the time.
Maybe a better way to express what I mean is "In bread recipes, all targets for time, temperature, and fermentation are necessarily moving targets".
I think maybe it might have something to do with yeast activity versus bacterial activity. A long ferment with a tiny bit of starter (a la 'do-nothing' bread) makes for a mighty sour bread! Of course, that's at room temperature which will also favour one over the other.
The reasons to use a pre-ferment are to increase the dough's strength (through more acidity), to increase it's shelf life, to improve flavor and aroma, and as you already mentioned, to adjust for timing issues of your bulk fermentation. The nice thing about PF, is it can also be used to impart certain flavor characteristics or handling properties.
For example, if you use a high hydration PF (eg poolish), you favor more enzyme activity (amylase, protease) which give you a more extensible final dough. It also gives you a slightly "nutty" flavor. If you use something stiffer (eg biga), you favor more acidity and a stronger final dough with sweeter notes. In that case, it would be good to do an autolyse.
By using more or less of a PF, you impart more or less of these properties to the final dough. If your percentage of PF becomes too high, you risk weakening your dough and negatively impacting flavor and aroma. What would be the difference between 100% PF and just doing a 12 hour bulk fermentation? Not much. In both case, you'd have a poor quality bread.
Now when you are mentioning a biga and poolish, I think, those are typically associated with a yeasted pre-ferment. So, other than a sourdough starter, a similar question would be how you determine how much yeast you use in the pre-ferment and what effect that amount has on the final dough (aside from the fermenting time)?
Also, could you explain why the acidity increases the dough strength?
You typically use a very small amount of yeast in a preferment, assuming you are doing a 12 hr fermentation time. A good starting point is 0.1% yeast and about 0.3% salt. The salt is used to slow it down a bit over that long fermentation. This tiny amount of yeast has little effect on your final dough fermentation. It is the fermentation activity in the PF that imparts all the properties you want. Since your final dough will need a much shorter fermentation time with a PF, you would use less overall yeast than if you had no PF. I hope that makes sense.
I am not qualified to tell you why acidity strengthens the dough on a molecular level, but acid does encourage gluten strands to bind more tightly together. The result is a stronger gluten network, aka, a stronger dough.