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From what I understand, the all-grain brewer warms up water to a particular temperature (usually 10-15*F over the strike temperature), adds this warm water to the grains in a mash tun, in an attempt to hit a particular temperature (around 145-160*F depending on the grains/style of beer), and then dumps the wort after an hour. I also understand that it is important to keep the temperature of the mash tun consistent at the desired temperature for this entire time; this is why a cooler is recommended for beginners.

However in a few YouTube videos, I've seen the all-grain brewer feed in a temperature probe into the mash tun and leave the cooler lid slightly ajar to allow for this. To an extract brewer like myself, this looks pretty silly, as the temperature would remain more consistent with the lid fully closed.

Is there a risk that (even in a cooler mash tun) the temperature might drop significantly enough to warrant additional hot water, such that measuring the temperature is more important than closing the lid completely? Or is there something else I am not considering?

At the same time I would LOVE to use my RaspberryPi to record this temperature. I'm thinking about drilling a hole for an airlock and feeding a temperature probe into the airlock (as I do with my carboys) to enable me to record the temperature of the mash tun while having an airtight environment.

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sigh. 3 answers and not one up-vote on the question. –  mdma Apr 21 at 12:58

3 Answers 3

I think the most important thing you need to accomplish is understanding your brewery. Begin by taking notes. Record the temperature every time you take it throughout the mash. But be sure that the temperature is uniform by stirring thoroughly, this can and will be a frustration for you.

Over time, you'll have a better idea for how much temperature you'll lose during the mash. If it's less than a couple degrees, you're most likely fine leaving the mash untouched the whole time. In this case, you might err on the high side for strike water and (again) keep good notes -- if the body of your beer seems off, adjust your strike water accordingly.

If your temperature changes much more than a degree F, it would be a good idea to re-introduce heat throughout the mash. A simple way to do that would be to add hot water when the temperature drops. However, this technique can be very tricky to pull off because of the difficulty in measuring consistent mash temperature and volume.

Other common techniques are to circulate the wort through some system which can add heat. Research 'RIMS' and 'HERMS' systems if you're interested.

Many commercial breweries use a steam jacket system. The idea here is the same as the mash tun - prevent heat loss in the first place.

In any case, especially as you're getting started, realize that you can easily make things worse when you try to make them better. For your first handful of batches, I'd suggest trusting the strike water temperature calculations, stir very thoroughly, and take notes.

The Raspberry Pi is a great instrument for reading temperatures. I'm working on a custom system which uses the Raspi, DS18b20 temperature probes, and Camco heating elements to monitor and maintain temperatures, and it has worked extremely well for me so far. I also use similar setups to maintain fermentation control. If you're interested in implementing something similar, I'll be happy to pass on some tips I've learned along the way.

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To underscore a point herein: no, you do not need to continuously monitor the mash temp with elaborate data-logging. Take a measurement when you dough in, about half-way through the mash after stirring, and at the end of the mash. Over time you'll understand the capabilities of your system. –  jsled Apr 21 at 12:28

"Continuously" is overkill, "Periodically" is more reasonable. In my experience there are many variables: the insulation of the mash tun and the ambient temperature are the most influential. I used to mash in a round 10-gallon cooler. When the ambient temperature was warm (70F+), and the mash volume was sufficiently large (4-5 gallons+), I found that the temperature would only drop by a couple of degrees in an hour. With smaller volumes and colder temperatures, it would drop more quickly. Over time, I learned what to expect from that system, and, when I knew the conditions were favorable, I often did not check it until moving to a mash-out step.

I now use a converted 1/2 keg for my mash tun in a RIMS system. Brewing in the winter, I see that the heater element is on almost constantly, where in the summer it is off for the majority of the time.

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Based on my experience, yes. Or rather, YES!

You'd think that, with sufficient paddling, a uniform temperature should stay fairly uniform. I haven't found that to be the case. I'd hit (e.g.) the protein rest, stir the crap out of the mash, check and recheck the temp, and when I came back 10 or 15 minutes later it would be 10 degrees hotter in the middle, cooler at the edges. Seems to me that, unless you have an extremely well-insulated mash tun, plus some kind of auto-stirring device (right, like any of us can afford that) you need to watch it like a hawk. And keep stirring.

Re: point 2, I'm not sure that an airtight environment is necessary or even desirable, except in the interest of avoiding heat loss.

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you don't have to stir - you can recirculate the wort to even out the temperature. –  mdma Apr 21 at 9:52
    
And, no, you don't need an airlock, but you will need something water tight; weldless fittings and thermowell s are not uncommon for this application. –  jsled Apr 21 at 12:17

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