Author Topic: Pete-zza's water temp formula  (Read 1544 times)

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Offline Danes Dad

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Pete-zza's water temp formula
« on: December 30, 2005, 03:21:22 PM »
Pete-zza you had a very detailed discussion of how to achieve final dough temp by adusting water temp.  Discussion can be found at this link: http://www.pizzamaking.com/forum/index.php/topic,567.msg5212.html#msg5212

The formula is listed below:

     WT = 3 (desired FDT) - (RT + FT + MFT),

Currently I am limited to kneading my dough by hand, but can't hit the FDT using your formula.  I recently mixed some dough and ended with a FDT of 86F. I used a water temp of 71F.   Based on my room temp and flour temp I should have been able to use 92F water, but I think that would have increase my FDT even higher.

My formula should have looked like this:
71= 3(80) - (74 + 74 + 0).  Obviously my numbers don't add up. 

I'm questioning if the MFT for hand kneading should always remain 0.  If you hand knead for 45 minutes your resulting friction and heat would be alot more than if you only mixed for 15 minutes.
Danes Dad


Offline Pete-zza

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Re: Pete-zza's water temp formula
« Reply #1 on: December 30, 2005, 09:26:44 PM »
Danes Dad,

I have not done enough kneading of doughs by hand, and rarely beyond 15 minutes, to speak more authoritatively on the subject, but the simple answer may be that the mathematical expression for determining the water temperature to use does not work as well for the hand kneading of dough as with other kneading methodologies. The expression you referenced is intended to be used by professional pizza operators who make their doughs in a continuous fashion pretty much without interruption other than to possibly add ingredients to the mixer bowl.

If you temperature adjust the water temperature and knead doughs by hand for a period of time equivalent to what a machine might do (e.g., doubling or tripling the knead time), then you add a long delay to the process. During that delay, the dough has a chance to warm up--not so much because of the heat of friction from hand kneading but rather because of the warming effects of room temperature. The same thing can happen if you use an autolyse, particularly a long autolyse. The dough will warm up because of the effects of room temperature during the period of the autolyse and end up with a higher finished dough temperature. I suspect the same thing can happen if the dough making process is subjected to many starts and stops, as might happen for example if one stops a machine several times to examine the dough, reorient it, answer the telephone, etc.. In most cases, the finished dough temperature will not be off enough to worry about. I typically use 80 degrees F as a target finished dough temperature for calculation purposes, but being off in either direction by say, 5 degrees, will not usually affect the finished results. Even in your case, 86 degrees is not out of whack enough to be of concern. What you may want to do in your case is to lower the water temperature by several degrees below what you might calculate. That should compensate for some of the heat rise in the dough, whether it is a result of the effects of room temperature or hand kneading (which I still tend to doubt). The same thing might be done when an autolyse is used.

I hope you will report back to us if, through your experimentation, you can establish a more causal connection between hand kneading and a materially elevated finished dough temperature,

Peter

Offline pam

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Re: Pete-zza's water temp formula
« Reply #2 on: December 31, 2005, 03:40:49 PM »
I hope you will report back to us if, through your experimentation, you can establish a more causal connection between hand kneading and a materially elevated finished dough temperature,

The causal connection is that hand kneading introduces an additional source of heat that is not present in mechanical mixing. With mechanical mixing, the only significant additive source of heat is friction, both between the dough and the mixer and within the dough itself. In addition to these heat sources, hand kneading involves the radiative and conductive heat transfer from one's hands to the dough. So with a mechanical mixer, the dough hook starts out somewhere near room temperature, but with hand kneading, the "dough hooks" start out in the neighborhood of 93-94° F—normal core body temp is 98.6° F, but the skin rarely reaches core body temp.—and blood circulation ensures that something close to that temperature will be maintained throughout the kneading process. Combine that with the fact that:

a) humans are homiothermic (warm blooded);

b) the excess energy generated by muscular activity is expelled primarily through the skin as waste heat;

c) excess body heat is transferred more efficiently via conductive transfer than radiative transfer; and

d) at rest, the human body puts out approx. 18.4 btu/hr ft^2, i.e. every square foot of body surface (skin) puts out approx. 18.4 BTU/hr* (during strenuous exercise, the heat output can be as much as 40x that);

and it should come as no surprise that hand kneading introduces a significant amount of heat into the equation that is not be present in mechanical mixing.

Of course, calculating the requisite starting temp for the water would be damnably difficult, because one would need to know, inter alia, the amount of heat generated by hand kneading, which would depend on the level of activity (light, medium, strenuous), the surface area of contact, the mass of the dough (obviously, more heat is required to raise the temperature of a 2 lb ball of dough 1° than a 1 lb. ball), and the length of contact between between the hands and dough (kneading time), but if anyone feels the need to do so, be my guest! ;)

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* The skin surface area (Du Bois area) of an average adult body is approx. 19.36 ft^2, meaning that the average adult at rest sheds approx. 356 BTUs/hr—roughly the amount of heat put out by a 100-watt lightbulb—in the form of waste heat. The Du Bois area normally varies between 14 ft^2 and 23.7 ft^2, so in any setting the heat produced by sedentary adults will vary between 257 BTUs (75.6 watts) and 436 BTUs (128 watts).
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Offline Pete-zza

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Re: Pete-zza's water temp formula
« Reply #3 on: December 31, 2005, 05:23:56 PM »
pam,

Thanks for the analysis.

I, too, have read that changes in skin blood flow are most marked at the extremities of limbs (hands and feet) and less marked in the trunk and head. This is why hands and feet frequently feel cold first.

With the above thought in mind, I measured the temperature of my hands using a digital thermometer (the only temperature measuring device I have), and the temperatures were 83.7 degrees F (left hand) and 77.2 degrees F (right hand). Room temperature was around 71 degrees F. Since a warm body transfers heat to a cooler body, I assume this means that if the dough that is being kneaded is cooler than the hands, then heat will be transferred from the hands to the dough. Otherwise, the dough will transfer heat to the hands. If the measurements I took were correct and accurate, then I would think that it would be hard to add much heat to the dough to cause it to rise above 80 degrees F over a knead period of say, 10-15 minutes, and especially if you are not kneading in a particularly aggressive manner.
 
Sometime I will have to do an experiment to satisfy my curiosity on this matter.

Peter

Offline gottabedapan

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Re: Pete-zza's water temp formula
« Reply #4 on: January 01, 2006, 07:18:11 PM »
I, too, have read that changes in skin blood flow are most marked at the extremities of limbs (hands and feet) and less marked in the trunk and head. This is why hands and feet frequently feel cold first.

Actually, under normal conditions, what's happening is that the extremities are exhausting heat faster than it's being replaced by circulation and muscular activity. If the overall rate of heat loss of the body as a whole causes the body's core temperature to drop, the body will constrict the blood vessels of the extremities (vasoconstriction) in order to (attempt to) maintain the body's core temperature, thereby minimizing heat loss through the extremities, with the result that the temperature of the extremities drops relative to the body core, and thus feel "cold."

FWIW, somewhere around here, I've got a series of infrared photos of massage therapists doing their thing. Granted, kneading dough and giving a massage are not the same thing, although some of the hand actions are quite similar. The heat loss (as measured by the temp. differential between their hands at rest and at work) is quite impressive. I'll see if I can dig them up, but as I recall, it's in the neighborhood of 8-10°.


 

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