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.

Here are some pictures of brewing sessions using the microwave.

http://picasaweb.google.com/beermeister1/VariousThingsBrewing

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.

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.

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.

"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.

Hail those willing to persevere through failure on the road to great triumph.

Nice experiment brewman, but i'm sure

#1) the microwave heats really unevenly.

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is pretty obvious to anyone who's ever used a microwave!

feedthebear said:

I think its because microwaves heat objects from the inside out.

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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.

mysterio said:

Nice experiment brewman, but i'm sure is pretty obvious to anyone who's ever used a microwave!

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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 !

beer4breakfast said:

As far as I know, all of the edible objects that people customarily put in microwave ovens are comprised of molecules.

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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.

beer4breakfast said:

As far as I know, all of the edible objects that people customarily put in microwave ovens are comprised of molecules.

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And your point is...?

Brewman,

if you have the time and inclination you should try a little experiment.

set up four small mash's, and do them all with conventional methods, ie with water heated on the stove. For each grain bill, put the the grains in the Microwave for 0,1,5 or 10 minutes, do the mash and check efficiency. I would suspect that the microwave's are cooking the enzymes in the grain before they can convert any thing, so you should see a decrease in your efficiency correlating to the length of microwave exposure.

Microwave ovens work by causing the bonds between H-O in H-O-H vibrate faster in turn causing the water molecules to move around bouncing in to other molecules resulting in a build up of heat. Enzymes tend to be hydrophilic (ltn. water loving)and contain a lot of water molecules. Buy heating the grain directly in the microwave oven you are most likely causing those water molecules to heat up the proteins and rapidly denature them, like creating mini hot spots in side the enzymes.

If you where to circulate the wort through the microwave oven you might avoid this problem, by not exposing the grain to the microwave energy.

As far as I know, all of the edible objects that people customarily put in microwave ovens are comprised of molecules

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I may be way off here, but I interpreted his statement in my mind like this:

The molecules themselves are heated inside to outside, but that doesn't mean the object that is composed of these molecules is being heated that way. The object's molecules heat up starting with one's closest to the outside of the object, but those outside molecules are being heated up from the inside of themselves.

Just a guess

The reason for the poor efficiency is exactly due to what was mentioned in previous posts, that is the mash is being heated unevenly. The microwaves will be absorbed in the outer most inch (or so) of the mash, leaving the inside relatively cool. The outer 1 inch of the mash can get suprisingly hot, in comparison with the centre, and this is destroying the enzymes.
Two ways forward are to reduce the power of the microwave (either by the duty cycle or if you have a better model which allows you to adjust the CW wattage), and once you find that magic number that allows the heat to transfer from the outside of the liquid to the inside of the liquid at the same rate that heat is being dumped into the outside ... then your golden.
The other option would work as well (it was mentioned previously too), and that it is to stir the mash, ensuring the mash is at a uniform temperature.
FWIW, the reason a microwave heats water, and few other objects, is that the water molecur is an electric dipole (same thing as a magnet, but rather than being impacted by a magnetic field, it is impacted by an electric field) and the water molecules are continuously trying to align themselves with the electromagnetic energy, which is flipping around at 4.9 billion times a second (2x2.45 GHz). This action actually causes the molecules to 'butt heads', and send some flying around. The molecules flying around is actually what we call heat (fast moving particles are hot, slow moving particle are cold). Microwaves ovens will heat more than just water - consider raisons in a peice of raison bread. If you ever microwaved one of those the bread is nice an warm, but the raisons will burn the **** out of you!
Good luck brewman, let us know if you take this further!

the microwaves wouldn't denature or break down the enzymes would it?

the microwaves wouldn't denature or break down the enzymes would it?

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No, the microwaves themselves do nothing to the enzymes. The microwaves in the oven are not really any different from the microwaves in you cell phone (just much higher power). These microwaves are don't have much of an impact on any molecules, other than those that are electric dipole (eg water), and at that the only impact they have is to cause them to rotate and vibrate.
Other impacts microwaves can have on objects is setting up electric currents. But not a significant issue here.
The temperature in the outlying areas of the mash are reaching temperatures well above the temperature which destroys the enzymes, and that is the reason for the low efficiency. Brewman is getting some efficiency because there is a period where the temperature is ideal, but it very quickly goes beyond that temperature.

that is the mash is being heated unevenly. The microwaves will be absorbed in the outer most inch (or so) of the mash, leaving the inside relatively cool. The outer 1 inch of the mash can get suprisingly hot, in comparison with the centre, and this is destroying the enzymes.

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The microwave wasn't getting the wort that hot. I moved my temp sensor around and there was never more than 10C difference. Not enough to kill the enzymes from heat alone. And I stirred. Read my post. Heat and stir, heat and stir.

Something else was going on.

The microwave wasn't getting the wort that hot. I moved my temp sensor around and there was never more than 10C difference. Not enough to kill the enzymes from heat alone. And I stirred. Read my post. Heat and stir, heat and stir.

Something else was going on.

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From your first post, you mentioned that the mash was held at 66°C, and you mention that there is no more than a 10°C difference. Does that mean that you were measuring a worst case of 76°C?

iBeer said:

From your first post, you mentioned that the mash was held at 66°C, and you mention that there is no more than a 10°C difference. Does that mean that you were measuring a worst case of 76°C?

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Nope. Highest was maybe 68. Temps were usually on the low side when there was a spread. The heat loss from the bowl was high, even though it was in the hot microwave.

I found a 5 Gallon Gott cooler today. I'll be brewing with steam and the cooler this weekend. Stay tuned.