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Temperature adjustment with the microwave

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gary.turner's picture
gary.turner

Temperature adjustment with the microwave

Since the liquids in nearly every dough need to be tempered, I went looking for some straight forward, repeatable method to get the temperature I wanted. My answer was to use the microwave. The next step was to figure out how to get the right time for any mass of water or milk, and for any temperature change.


We can see that the time required (Sec) is proportional to the mass of the water (M) and to the change in temperature (ΔT), multiplied by some constant (C). 


M × ΔT = C × Sec


Rearranging to solve for the time; Sec = M × ΔT / C


With my microwave oven, the constant is 312.5 for weight in grams and temp in Fahrenheit. There's a kink in the formula though. My oven requires about 3 seconds to come up to speed, so I add that to the calculated time. For example, let's say I have 350g of  40F milk from the frig that needs to be 65F for an intensively mixed Vienna style dough. I need to raise the temp by 25F, so 350×25/312.5+3 yields 31sec to raise the temp to 65F.


How do you find your magic number? Measure some water, say in the 300-450g range. Take its temperature, and zap it for some reasonable time, e.g. 30 seconds. Measure the temp. Repeat with the same weight of water, for a different length of time. Plot the two tests on graph paper (or use a spreadsheet or graphing calculator), and extend the line through the points to where it crosses the zero temperature change line. Where it intercepts the zero temp, the time line will have some small value. That's your start-up time. Now multiply the weight of the liquid by the temperature change and divide by the time less the start-up time. For example, 350 × 25 / (31 - 3) = 312.5 Notice that that is from my own earlier example. Do the math on your other test(s). The C values should closely agree.


Once you have your magic number, any weight of water or milk and any (upward) temperature adjustment will provide the zapping time for your microwave.


cheers,


gary

Comments

AnnaInMD's picture
AnnaInMD

getting to 75 degrees F isn't all that difficult but maintaining this temperature for several minutes to hours is the problem.


 

gary.turner's picture
gary.turner

Hi Anna,


I don't understand your point. Are you talking about making some sort of water bath? In that case, maintain the temperature in whatever way you do so now.


My method simply allows you to achieve a particular temperature with a simple calculation that gives repeatable results. The impetus was the need to achieve the desired dough temperature (DDT) without depending on guesstimating the zap time for the liquid. For example, a DDT of 75F, room is 70F, flour is 70F and mixer friction factor is 10F. The water, which comes out of the tap at 60F needs to be heated to 225-70-70-10=75F. Let's  assume a 500g dough with 67% hydration. We need to heat 200g of water. Using the magic number, we have 200×(75-60)/312.5=9.6sec. Add the 3sec start-up time, and I'll zap the water for 12 or 13 seconds and come so close to 75F as to be scary.


Does that answer your question?


cheers,


gary

AnnaInMD's picture
AnnaInMD

My problem is maintaining a certain temperature when the house is at 67 degrees F during the winter. When mixing the dough and/or fermenting/proofing, the dough should maintain a certain temp which is so hard to do other than turning on the oven light which also is just a guess as it can get pretty warm if left on too long and certainly not at a constant level.  


Also, just adding the initial water when first starting to mix is tricky since the stainless steel KA bowl is quite cold. I try to rinse it first in hot water and then add the warm water. Truly a challenge in the winter.


Best,


anna

LindyD's picture
LindyD

Your method would work well for water supplied by a temperature controlled system, but that's not the case for most people who use tap water.


The temperature of my (well) water at home varies with the seasons and in the winter, the depth of the frost line.  Over the weekend my tap water was 40F (it was -20F outdoors)


While I do always compute the water temperature to attain the DDT, it takes me less than 60 seconds to achieve it.  No graphs, charts, or compute programs.  Just my Thermapen and microwave.


I guess one could refrigerate the water, but in my kitchen that would just be wasting space and energy, plus I like my water fresh from the aquifer.


Good system, however, when there's no temperature fluctuation and so long as you confirm the temperature before adding the liquid.


There's good logic behind the old saying:  Measure twice, cut once.

gary.turner's picture
gary.turner

Quote:
Your method would work well for water supplied by a temperature controlled system, but that's not the case for most people who use tap water.
You've missed the point of the calculations, Lindy. It doesn't matter the starting temp or the ending temp, only the difference. If you're raising the temp 20°, it doesn't matter where you start, you'll be 20° warmer when you end. If we both need 75F water and you start with 40F and I start with 60F, you need a 35° rise and I need a 15° rise. Those are the numbers we will each enter into the calculator.

Establishing your own number will let you alter the temperature without guesswork. All you need to know is how much water and how much temperature rise.


I don't doubt you've gotten pretty good at estimating your zap times, I have also. But, doughs ranging from 500 to 2000g and hydrations from 60 to 70%, and varied temps are just too much for my head to keep up with.


cheers,


gary

MikeSwifty's picture
MikeSwifty

For the "magic number" you plot time spent in the microwave vs. temp change of the water, is that correct?  I'd like to give this a try but not yet sure what I'm doing. :-)

gary.turner's picture
gary.turner

Right. For the tests, be sure that the weight of the water is the same for each try. As I recall from school days, a long time ago, that's called normalization; one less variable to deal with. ;-)


cheers,


gary

LindyD's picture
LindyD

I'm low tech by choice in a few respects.  I know there are spreadsheets for many aspects of baking, but for me a piece of paper, a pencil, and a calculator have worked pretty well.


Maybe I'll think differently once I get my iPad and discover an app for that!  ;-)