November 14, 2011 - 5:09pm
Fermenting and Proofing Max temps…..why?
I just had someone ask me why he couldn't ferment his dough at a higher temp. since yeast cells can live up to 140° F.
I haven't read anything about this but what I have read suggests that optimum fermenting temps. are around 77° F so I am guessing that if one goes above that and proofs at 100°F they run the risk of damaging the yeasties and beasties.
I would also guess that at a higher temp. the bread would proof way to fast to have any flavor because the LABs need time to do their thing....
Just guesses on my part with what I have gleaned here....
Anybody have a more 'scientific' explanation?
Thanks,
Janet
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If the proofer is too warm you will get a lot of rise on the outside portion while the interior is still cool and not done much proofing.
Gerhard
When the temperature inside the dough reaches 122º F, the starch granules start to swell and the yeast start to reach a dying stage. At 140º F, the starch begins to gelatinize. Under the effects of heat, the starch granules burst and liberate many chains of starch which form a very complex, gelatin-like matrix that will, after cooling, create the crumb of the bread.
"SFBI Newsletter, Spring 2002"
Jim
In addition to all the above answers:
His question would make sense if yeast got faster and faster and faster all the way up until just before it died ...but it doesn't work that way.
Maybe an analogy with humans will help. Suppose I won't be dead until 100 (I can dream, right?), and will still be alive at 95. But at 95 with my cane and walker, I won't be besting any teenagers in any footraces.
The best growth rates for various yeasts are generally between 70F and 80F.
Although carefully jacking up the temperature may not completely kill yeasties, it won't make them grow all that much faster either.
Between 33 F and 100 F, commercial yeast activity will double in speed for every increase in temperature of 18 degrees F (or 10 degrees C). Between 100 and 140 F, yeast will start to slow down again (I don't know the rate of decrease). At 32 F and below yeast activity pretty much stops. So the fastest fermentation rate is between 90 and 100 F. A dough temperature of 77 F will take twice as long to rise as a dough temperature of 95 F. One thing to note is that this is for commercial yeast. I believe that most strands of wild yeast do not tolerate these higher temperatures (but am willing to be corrected on this if someone knows otherwise).
Using the above rule is very helpful to professional bakers seeking to time their bread. For example, if a dough with a given amount of yeast is known to rise in 1 hour in a controlled environment of say 77 F. In order to extend this to a 2 hour rise, the baker can drop the temperature to 59 F and still know when the dough will be ready. This might affect flavor but it is one more tool used to make the dough predictable (another is knowing the amount of yeast to use for a given rise time).
A slower rise can help flavor, so it is not always advisable to speed things up. I would venture to guess that this is the main reason you are finding that 77 F is normally recommended.
Hope that helps.
-Maverick
Hi Janet,
In addition to the comments made about the effects of higher temperatures on the starch molecules found in the dough, the aspect of flavour profile is all-important.
My understanding is that the optimum temperature for yeast activity is 37*C....ie our body temperature. Dough is originally mixed somewhat cooler than that as part of the process to control fermenting activity, and allow for the development of good structure within the dough; this is not possible if the temperature gets much beyond 30*C.
Final proof is not conducted beyond 45*C for a few reasons. Chuck's comment about slowing down at the higher temperature is quite correct. Of just as much importance is that the dough will begin to develop a quite unpleasant flavour profile if subjected to these high temperatures during any phase of proof.
Best wishes
Andy
Thanks to all who responded above.....I hadn't thought about the effects on starch molecules....makes sense.
The information will be passed on :-)
Janet
Janet, there is an interesting plot for two strains of wild yeast that can be seen at the link below:
http://www.rockisland.com/~rkg/scienceofbaking/effect_temperature_culture.htm
It graphically makes Chuck's point very nicely, if you are graphically inclined.
Ron
One observation I will share is that when baking during a heat wave this past summer (110-155 degrees during the day, upper 90's in the house even with AC going) dough would proof incredibly fast. This would cause a loose, moist dough that didn't always hold it's shape very well when doing a boule loaf. Did make for some fast baking (1 hour first rise, 40 minute second rise).