Mass Effect
In "Bread". Hamelman writes that he used to think wrongly that larger batches of dough developed (gluten) faster than smaller batches. However, larger batches of dough do ferment faster.
He explains that smaller batches develop gluten faster because each turn of the mixer in a small batch manipulates a higher percentage of the dough than in a large batch.
He doesn't explain why larger batches ferment faster. He also writes that home bakers who scale down his formulas for commercial batches of 12-15 loaves (I typically divide his metric formulas by 10 for two regular loaves or one double) should increase the amount of sourdough culture by 25%. I've seen other references to the "mass effect" and it certainly is real, especially with sourdough. But why? https://en.wikipedia.org/wiki/Exponential_growth explains
The formula for exponential growth of a variable x at the growth rate r, as time t goes on in discrete intervals (that is, at integer times 0, 1, 2, 3, ...), is
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That's fine, but when I run the numbers for different batch sizes that start with the same percentage of culture, the percentage of culture as the dough ferments increases exactly the same across all starting batch sizes.
So what's the source of the mass effect and why are smaller batches more sluggish if they start with the same percentage of culture?
Thanks
Is it possible that larger doughs maintain their temperature better than small?
Smaller surface area/volume ratio in larger dough?
I have the first edition of Bread. I have not been able to find his instruction to increase the culture quantity. Where does he mention this in the 3rd ed.?
I copied and pasted “Due to the small mass of the home sourdough, ripening could be slightly sluggish, and an increase of perhaps 25 percent more of mature culture can overcome that sluggishness” into my notes Bread Formulas but I'm damned if I can find it again in the book.
You might be right about the surface area / volume ratio, which, for a sphere, would be 3/r
I don't know for sure but fermentation liberates heat. So a large mass of dough would heat up more than a small mass, and thereby ferment faster. See, e.g.,
https://www.homebrewtalk.com/threads/how-much-heat-does-a-fermentation-produce.145767/
Sure, but wouldn't the heat generated be proportional to the weight or volume?
Yes, and a large mass of dough would have less surface area, proportionally speaking, relative to the amount of heat it generates. This would cause a temperature rise and faster fermentation.
You may have cracked it. I've asked the Bread Lab at WSU what they think.
My vote is for the weight of the dough. Most chemical reactions and thermodynamics would use mass (moles, really) for quantity of material.
I've been writing "mass" a bit carelessly, but for a fixed dough formula the weight and mass will be proportional. So no need to be picky about the units. Weight, mass, moles, they all work here.
I'm not picky about the units. I'm just used to to using the term "mass" instead of "weight" because of all the years in chem the lab.
One of the sayings of a professor in college was "fish have scales but chemists have balances." Of course, probably none of us here actually use a balance instead of a scale, although I do have an old Ohaus Dial-O-Gram triple beam balance with magnetic damper that I use for non-food applications.
ob1035.jpg
I'm sorry I put it like that. It has a negative connotation that I didn't mean. Love the scales vs balances!
TomP
I used a balance in a community college baking class. Resizing formulas in lbs and oz was a PITA. And modern electronic scales can handle the same weights balances can, with more accuracy and ease of use.
My one positive experience with a balance was explaining to a classmate who was a vastly more skilled baker than me how to resize formulas in lbs and oz - he was a great cook and baker, and a very nice guy, but a total bust at arithmetic.
Much like the use of the terms weight and mass interchangeably, scale and balance also tend to be used interchangeably, even by a major vendor like Mettler-Toledo. The difference between a electronic scale and an electronic balance is the type of weighing sensor used. Analytical and precision balances will have a more sophisticated sensor that measures the force required to compensate the displacement of the material on the pan.
These balances are calibrated before use at the installation site (including what building floor they are on) so that they account for gravity and accurately measure mass (instead of weight). They also have higher performance specifications with respect to linearity (accuracy through the entire range), repeatability (precision), and eccentricity (off-center accuracy). Of course, you have to pay $$$$ for this performance. Most scales used by bakers will be <$100, but even an inexpensive precision balance will be several hundred $$.
What type of balance did you use in the baking class? Mechanical or electronic? Was the balance a PITA because it read in lb/oz? The electronic balances I have used in the lab had the ability to read in different units.
Calibrating scales for the floor they are on (and presumably any significant local gravitational anomalies, like big iron deposits) still measures weight - the force of gravity on the thing you're measuring. The calibration to local gravity allows you to interpret that measurement as mass.
The community college baking class used old-school mechanical balances with weights in lbs/ozs. The balance had two plates; first you zeroed out the weight of the bowl for the ingredients, then you set up the weight you wanted (IIRC the weights were in lbs; you could read oz by sliding a weight along the oz scale).
The chef instructor was an incredible cake decorator and that's what he focused on; I was a disaster. I wanted to do some kind of bread project at the end of each semester, but it had to be a decorated cake.
During the 2008 housing crash, we had to make a gingerbread house during the holiday season. I knew mine would be a disaster so I decorated it accordingly. I got the 2nd lowest grade in the class (the other guy's house collapsed). But local print and TV reporters invited to look at the really nice work, loved the humor in mine. And the next day after I made the local news, Jay Leno came out and said, "The housing crash is soooo bad .... that I saw a gingerbread house that had been repossessed".
Scroll down past the BBQ photos in the album at the link to see my lousy gingerbread house. And then the financial collapse cake I made the following semester. But if you keep going eventually you get to some gradually improving breads.
Culinary Photos
Thank you for clarifying weight and mass with respect to weighing instruments. I'm embarrassed to say I had it the other way around (physics is definitely NOT my strongest subject). I was misled by the description of the ”electromagnetic force restoration” transducers to incorrectly mean that they were measuring mass independently. Even many balance vendors get it wrong, although I found that Mettler-Toledo did indeed explain it with lots of equations! I always like learning something new, especially when I had it wrong.
I really like your gingerbread house! It's too bad that the judges didn't have a sense of humor; at least Jay Leno did. And I'd say your early challah looks great; I don't have the patience for braiding.
Thanks for your gracious comments. In terms of baking/decorating skills, my project was a POS (piece of ...) so I can't blame the chef instructor for the lousy grade. Ultimately I got B's in his two classes because I was always on time, had my tools, and washed my hands - that will get you through community college.
I bake the challah once a year, for our Thanksgiving hosts, maybe another time for some special occasion. Rolling out the strands in a real PITA and I'm not very good at it. My last couple of 3-deckers have been lopsided, if tasty.
Now measuring and baking in space would be something else!
LouisCohen: You asked: So what's the source of the mass effect and why are smaller batches more sluggish if they start with the same percentage of culture?
The fermentation process creates some heat which will cause the temperature of a dough mass to increase.
As we know, higher dough temperatures result in shorter fermentation times (faster rates of fermentation).
A dough mass will cool where its surface is in contact with the walls of the mixing bowl and, but less so, where it is in contact with the surrounding air (i.e. the top of the dough mass in the mixing bowl).
The mass effect comes into play when the ratio of a dough's surface area to its volume (and, hence, weight) is taken into consideration. If we think of our dough ball as a perfect sphere, we'll find that the ratio of surface area to volume (and weight) decreases as the size of the dough ball increases.
Since the rate of cooling of a dough ball is directly proportional to its surface area, and all other things being equal, the larger the dough ball, the more slowly it will cool. This is the mass effect.
In practice, for home mixers, the mass effect is pretty small and can be ignored.
For commercial sized batches, somewhere around 10-20 lbs and up (depending on the mixer geometry, too), the mass effect becomes significant. This is why bakeries will use adjust their formulas (yeast, levain) and use cooled water to keep their dough temperatures under control.