Quick Advice Needed - Mash Temperature

[Raize]

I had a bit of a disaster with today's brew, an Oktoberfest using 4.25kg of Munich Light as base malt.

I forgot about the pan heating with grain in it, and when I got back to it, the temperature on the sensor was 84C.

After stirring/mixing it a bit, the temperature was 72C.

After throwing in some ice cubes it was 70C.

It took about an hour to rise from a 55C protein rest to the temperatures listed above, at a fairly steady rate.

How much of a starchy mess is this going to be, is there any point pitching yeast?

[vacant]

In that 55-84C hour the conversion was done. I read somewhere sparging/mash out shouldn't exceed 76C or 78C but I bet that includes a safety margin. I'd pitch.

[Raize]

I left it sitting another hour during which it dropped from 70C to 63C.
The liquor is sweet to taste, that's probably a good sign.
The pre-boil gravity is 1030, corrected for 63C that's 1045. It should be about 1048 after the boil; my target was 1052

I'll pitch and see what happens. Worst case scenario is I get liquid bread, plus a nice yeast cake to start my doppelbock on.

[Kev888]

If mixing brought the temperature back down that far, then at least some of the mash would have been far cooler than the sensor was indicating; in fact cooler than normal mash temperatures. So there would have been at least some enzymes still viable for the mash, and (as Vacant says), at such a slow ramp rate even the denatured ones would have worked for a fair while. Overall, it seems likely you'll have got a reasonable conversion.

The overheated portion of the mash wasn't (of course) ideal, so there may be some effects such as increased astringency, haze and a higher FG than intended (through favouring the alpha-amylase temperature range). So it may not be the beer you were expecting, but I'd be surprised if it was actually undrinkable.

[Fil]

iirc the denaturing temp for the enzymes is circa 85C, so it your thermometers are on the money you may have just scraped by ok

but to be sure an iodine test will indicate residual starches, and if black as coal, a handful of fresh grain well mixed in should revive the enzyme population/count?

[Kev888]

It is a combination of both temperature and time, so hard to give a specific temperature threshold, and activity is perhaps more meaningful than complete denaturing (i.e. with nothing at all happening). But certainly enzyme activity drops off ever more quickly with increased temperature; for years I struggled to control fermentability of the sugars, before realising that it is 'far' from linear, and most of the effect is in the upper few degrees of normal mash temperature.

Depending on who you believe, beta-amylase activity can plummet to very little within 15mins as it reaches around 70c, whilst alpha amylase will last considerably longer, or take several degrees more for the same effect. But if time is allowed, each will dribble on for quite a while (so the beta amylase can still have a surprising effect on long mashes), until they are completely denatured.

In this case it is hard to call. Part of the grain-bed temperature rose to largely knobble the beta-amylase, and the alpha-amylase activity would have been minimal at best. But.. it took quite a while to reach that so during the gradual rise things would have been working well. Plus other parts of the grain-bed were cool for quite a while before mixing in, so the beta amylase may have got a head start (in those places) before the ultimately high mash temperature (favouring the alpha-amylase) resulted.

I expect that it will have worked/converted fine. My guess (and it is only that) is that the overall fermentability of the sugars may have averaged out to give a high-ish FG but nothing remarkable.