Very odd question: reheating fermented beer

Here is my story. I brewed a stout a couple of weeks ago. I did a step infusion in my kettle and my last step I left the friggin burner on

Anywho, my mash spent a good amount of time in the 170+ range and thus had a lot of unfermentable sugar. Fermentation died out at 1.030, down from 1.056. I have read about adding enzymes to the wort to break down the complex sugars and get fermentation going again, so I bought some Amylase Enzyme from AHS. Added this to my wort last night and within a couple of hours, fermentation had taken off again.

This is all well and good, however, I have heard through my perusing that when adding enzymes like this, it is possible for the enzymes to completely break down all the complex sugars and end up with FG around, or even below, 1.000. Obviously this is not something I want, especially on a beer like a stout.

So, I was thinking about how to stop the enzymes in their track once I get to a SG that I am comfortable with. The only thing that I can think of is to raise the temperature of the wort to 165ish and let the enzymes break down. What kind of risks am I taking doing this approach? Obviously I will be killing my yeast. I do keg, but I think I am going to bottle this batch. So, as long as I add yeast when i add my priming sugar, that should take care of that. Is there any other potential risks that I am overlooking?

I would NOT heat it. You will almost certainly evaporate most of the hop flavor/aroma, and risk boiling off the alcohol is you reach 171f. What I would do is add campden tablets to kill the yeast that are in there and arrest fermentation. Campden tablets finish their work in about 24 hours, but I'd wait longer. Then, when you bottle, you just add back a bunch of rehydrated dry yeast.

But I still doubt that amylase will bring your SG down that low. So just wait and see...check your gravity often.

Yes, I do plan on checking it regularly, and as you stated, if it is not a problem then it is not a problem. If it stops at a reasonable gravity, I will just let it be, but I have read that people who have used enzymes on stuck fermentations have had them get too unstuck...or something.

As for the Campden tablets, I have never heard of them. A quick google search makes it look like they are used in wine? How many tabs would you recommend for a 5 gallon batch?

The [alpha]-galactosidase in Beano will do exactly what you fear, because it is active at low temperatures. Amylase is less active at room temperatures and at kegger temperatures it basically stops.

I'm in the middle of an experiment using Beano & then heating to de-nature the enzyme. 140F is all it takes. I lost 0.05 Brix in the heating process in one ale and 0 in the other and don't detect any difference in flavor. I now have two soda bottles of re-heated ale sitting on the counter (with new yeast) to see if any more breakdown &| fermentation occurs.

Typically, 1 tablet per gallon, but that only stops the yeast, not the enzyme.

So, assuming this beer goes below where I want it (or at least is acting that way), if I keg it and let it be, you think the amylase will stop and therefore fermentation will stop. That would certainly be easier and less risky. And since I got two more kegs on the way, it wouldn't be problem with taking up valuable keg space:rockin:

anything over 170F can start extracting tannins from the grains. tannin 'astringent' flavor doesn't age out over time.

malkore said:

anything over 170F can start extracting tannins from the grains. tannin 'astringent' flavor doesn't age out over time.

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Well aware of that. I had zero intention of leaving the burner on. Just one of those things. However, I always taste my hydrometer samplings, and I have tasted nothing that would be described as an off flavor and especially not astringent. It was just really sweet, as you would expect 1.030 beer to be.

I neglected to add that alpha amylase also has a de-branching limit, so you'll always have some of the larger malt chains around.

david_42 said:

I neglected to add that alpha amylase also has a de-branching limit, so you'll always have some of the larger malt chains around.

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That's good to know. Thanks for the info and all the other previous help. As of last night, it still had a nice little krausen on it and was down to 1.021. I am starting to believe that I am going to be able to save this beer. Thanks again.