Suggestion re calibration of 'heat source'

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Suggestion re calibration of 'heat source'

Postby billvelek » Sun Dec 31, 2006 2:50 am

Although I had calibrated my mash tun some weeks ago, I never bothered to calibrate my heat sources until this morning, since I'll be brewing again today. Compared to calibrating my vessels -- which permited me to simply check temps after set time periods (5 and 65 minutes) -- I found the method for calibrating heat sources to be somewhat awkward and probably slightly inaccurate, as I'll explain. The prescribed method is to time how long it takes to increase the temp of water 10C or 18F. To begin with, that approach pretty much requires a user to stand over the pot to watch the thermometer, rather than just setting a timer and then taking a reading at the buzzer. If I were using my old thermometer, I would also have to either hold the thermometer by hand or take repeated readings, because it did not have a clip. And using this method precludes having a lid completely on the pot, which is the way I always heat until I get a boil going, so I think that this probably throws the measurement off slightly from what it would ordinarily be with a lid on. Since this is just a basic math formula with time and temp the only two variables, why not either replace the current procedure with one that measures the amount of increase in temp after either a set amount of time, or a variable time that the user would insert, or else provide my suggestion as an optional alternative method.

Also, is it necessary or recommended that the same heat source be calibrated for each kettle? For instance, I can put a quart pot on my kitchen stove, and water will boil very vigorously. A 5 gallon pot on the same burner will boil, but not as vigorously -- no doubt due to the amount of heat that is radiated and conducted by the larger surface area of the pot and water evaporation on the larger water surface. My 7.5 gallon turkey cooker is even worse (much slower sustained boil -- almost just a simmer). So I think that it just stands to reason that if larger pots lose more energy than smaller pots, then that can affect the calibration process as well.

I'm still not entirely sure what the heat source has to do with anything, including mashing. I am always prepared to instantly meet each infusion temp. I keep a very large pot boiling on the stove, and blend boiling water with faucet water into a smaller pot that is used for the transfer; I check the temp and make adjustments to achieve temperature, and then quicky make my volume adjustment by dipping out a large amount and then slowly returning water until I attain my required level. I measure with a thin stainless steel ruler that has almost no displacement: 2" = 1 gallon, exactly. My volume adjustment takes only a few seconds once I have the temp right, so I don't think there is a problem with it cooling off in the process. But my point is this: I have boiling water available when I need it, whether it took 1 hour or 10 hours to reach a boil, so I still remain puzzled.

EDIT: Of course, I can see how it will be relevant for a decoction, or a RIMS or HERMS.

Cheers.

Bill Velek
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Postby Brant » Sun Dec 31, 2006 8:34 am

I used a digital thermometer with a high-temperature alarm to make sure I didn't miss the mark. Good point about the lid not being completely on affecting heating times, though.

I think an important point to remember is that the "heat capacity" calculated for your various kettles should cause the "heat transfer" value of your burner to calculate to roughly the same value, no matter which pot your are using. That is the reason the Heat Source calibration requires entering the heat capacity of the vessel in which you are heating the water. I have not experimented with multiple kettles to see if that in fact works out, though.

I agree that with the way you heat your infusion water, there is no benefit for you to use the Heat Source feature in BTP. For me, I like the Mash In step telling me how long it will take to heat my strike water, because I heat to the target temp, and then just dump it all into the tun. In fact, I wish the Infusion and Separation steps would also tell me how long it will take to heat the infusion/sparge water, because there have been plenty of times that I have not "stepped back in time" far enough to start heating my mash out infusion. And I do decoctions for particular styles, and yes, the heat source is valuable there.
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