The question I had is what would happen if you fed a Blueberry Yeast Water/Bread Flour levain additional Blueberry Yeast water, using seeds from previous levain builds. Namely, what is the effect of increasing population of blueberry yeast over a series of builds while holding the overall volume constant. Would there be an improvement or degradation in rise times or volumes? Would there emerge a limit as to how quickly a doubling or peaking would occur? Would it explode into a new black hole? These were the questions that I just had to answer for myself.
Methodology
I started with 10g blueberry yeast water (BYW) and 10g Bread Flour (BF). This was left to rise to its maximum height and plateau, whereupon it was chilled for the night. The next morning 7 grams of this levain was fed 7g BYW and BF, and again left to rise to it’s maximum height and plateau, then chilled or refreshed. Using time-lapse photography (thank you RonRay), I was able to track the level of growth for each build on 15- minute intervals. I intended to continue this refreshment pattern and observe the action until the growth/plateau cycle was found to closely resemble the previous builds or something else happened to draw my attention away.
Findings
The following graph shows the results.
Just looking at the doubling times, clearly the more iterations of builds shortens the time required for the levain to double. R1 took almost 7 hours to double, whereas R2 took 5 hours, and R3 took 2.5. Most of the trials R3-R7 in this 2-2.5 hour range to double. By far the fastest doubler was R8, at just 1.5 hours.
There is also interesting phenomena with respect to the period of growth before plateauing. R1 took about three hours take off, presumably adjusting to the new food/environment, and didn't fall off until almost 8 hours after the first feed (5 hours of active growth). R2 took an hour get going, but fell off an hour quicker than R1, (six hours of active growth. R3 didn't lag at all. It grew from the time that it was fed and continued steadily for almost 6 hours. R4-R6 all took off from the get-go, and enjoyed a solid 4-4.5 hour growth stage before plateauing. The standouts were R7 and R8, which both not only took off from the start, but also, grew for an astonishing 6 hours before exhaustion. So something about more yeast in the culture allowed for a longer growth stage, despite a finite and constant supply of food.
The peak volumes also varied with the yeast concentrations. The lowest amount of yeast, R1 was barely able to double (2.3X) before giving up. R2 was slightly better at 2.5X. R3 and R4 made it just to 3X. R5 and R6 got to 3.5X, but again, look at R7 and R8. They got to an impressive 4X! It took them a long time, but they never lagged, they just kept going, and going and going.
From a temperature perspective, there is apparently an outside, uncontrolled effect. As we can see, the cycles R3-R8 closely track each other. The cycles of R7 is very similar to R5, both of which were started first in the day, from seed chilled overnight in the refrigerator. R8 proves to track closely with R6, indicating a typical afternoon pattern. So there may be a distinct positive effect from room temperature (it gets hot in the afternoon here now (86*F+).
In conclusion, I believe a YW builds should be fed subsequent builds with more active YW until a doubling can be achieved within about 2 hours and the capacity of growth is around 3x or more, usually by the third build. Given the time and desire for even stronger levains, subsequent builds using active yeast waters will not have a detrimental effect on your doughs, although some care should be taken to avoid overproofing.
An aside... In a separate experiment, I discovered that this Blueberry Yeast Water is the least effective of my collection, bested by far by the Cherry Yeast Water. I intend to repeat this analysis using the Cherry Yeast Water instead.
Again Stay Tuned...
-Pamela
