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Old 02-11-2007, 02:31 PM   #1
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Default Microwave mashing DOESN'T work

I've been brewing some test beers, 3 gallon batches, in my kitchen.

Because the mash schedules call for step mashes and the batches are small, I've been mashing them in the microwave. I did 2 batches like this, both with the same result.

Last night I mashed 5 pounds of grain with 5 litres of water for 2 hours. I have a digital temp probe. I held the mash at 66C (151F) or a little higher for most of the 2 hours. I transferred the mash into a double pail sparge setup and fly sparged it for 40 minutes.

The outcome was 3 gallons of wort with a SG of only 1.020 ! I've never suffered from low efficiencies prior to using the microwave for mashing.

There could be 2 causes as far as I can see.

#1) the microwave heats really unevenly. One has to heat and stir and heat and stir. My mash vessel was just an open plastic bowl. Heat was lost from the top and the sides. So even though my temp sensor said 66C (151F), parts of the mash were at higher or lower temperatures. Last night I specifically mashed for 2 hours to compensate for this.

#2) the microwave action might kill the enzymes.

As far as I can tell, the rest of my process was always like it was before, and I always got good efficiencies.

Next week I will try using steam to heat the mash vessel and the mash vessel will be a small cooler.

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Old 02-11-2007, 05:37 PM   #2
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Here are some pictures of brewing sessions using the microwave.

http://picasaweb.google.com/beermeis...sThingsBrewing

I don't know why it didn't work. After sparging, I tasted the grains and there was no sweetness. I don't think they converted to sugar. I've never had a problem with getting good efficiency before !

My next brew session will use a small cooler and a steam generator. Stay tuned.

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Old 02-11-2007, 06:06 PM   #3
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I think its because microwaves heat objects from the inside out. Also microwaves don't heat up water nearly as well as they heat solids.

So while the water was at the temp you wanted it, the inside of the grains where the enzymes and sugars you were trying to get were much hotter and getting converted to something else or being destroyed.

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Old 02-11-2007, 06:21 PM   #4
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I'd say #1 & #2. Even with a rotating platform in my microwave, I observe hot spots. Since all of the mashing processes are very temperature sensitive, you might get a microwave to work if you have one that regulated the power output directly (rather than cycling), had a rotating platform AND a counter-rotating mash paddle.

I'm looking at steam for decoctions. Seems you should be able to drain the wort, steam heat the grain, then put the wort back without de-naturing the enzymes.

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Old 02-11-2007, 08:03 PM   #5
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"Also microwaves don't heat up water nearly as well as they heat solids."

You got that backwards. Microwaves heat up water better than anything, or at least better than 90% of the solids out there.

"I'm looking at steam for decoctions. Seems you should be able to drain the wort, steam heat the grain, then put the wort back without de-naturing the enzymes."

Look at my steam posts in the equipment forum. My next brew session (next weekend) will use steam. I'll report my findings. I'll be injecting the steam right into the mash vessel.

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Old 02-11-2007, 10:33 PM   #6
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Old 02-11-2007, 10:35 PM   #7
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Nice experiment brewman, but i'm sure

Quote:
#1) the microwave heats really unevenly.
is pretty obvious to anyone who's ever used a microwave!
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Old 02-11-2007, 11:27 PM   #8
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Quote:
Originally Posted by feedthebear
I think its because microwaves heat objects from the inside out.
In fact, microwaves heat MOLECULES from the inside - out, not objects. An object is going to heat from the outside - in, just as it would with any other form of cooking. Half-cook anything frozen and see.
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Old 02-11-2007, 11:38 PM   #9
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Quote:
Originally Posted by mysterio
Nice experiment brewman, but i'm sure is pretty obvious to anyone who's ever used a microwave!
I guess you know it all. *nods

I thought it was worth trying. And notice how I share my "failures" so that others learn. I mean, I didn't have to write this up, did I ?

I thought stirring it would overcome the uneven heating. And it does, actually. Its more the heat loss of the vessel that makes the temps uneven.

Thanks for the encouragement, fifelee !
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Old 02-12-2007, 12:01 AM   #10
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Quote:
Originally Posted by beer4breakfast
As far as I know, all of the edible objects that people customarily put in microwave ovens are comprised of molecules.
Chances are the microwave is filled with molecules ! Air, plastic, water grain, etc. They are all molecules !

The real deal is that certain molecules absorb microwave radiation better than others. Air is a very poor absorber of microwave radiation. Water is pretty good. So the microwaves penetrate as far as they can into the substance, until the radio wave power has dissipated. With my mash, that caused the side near the microwave power supply to heat faster or only the side near the microwave power supply to heat at all.

This week I mashed a 5 pound grain bill. Last week it was a 3 pound grain bill. Last week worked much better than this week.

Anyway, it doesn't heat evenly. The problem might be less pronounced if the mash was small enough to fit in a container that could rotate on the turntable.

FWIW, I think a microwave would work OK to heat wort circulating in tubes in the heating chamber. But I'm going to try steam first.
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