I do BIAB and in my constant search for ways to simplify my brew day I recently started to heat my mash with the grains already in. That is:

  • I fill my kettle with the full water volume I'll be using (~27L). Water is about 10C this time of the year.
  • I dough the bagged grains in. The bag is bound by a string and kept slightly off the bottom of the kettle.
  • I apply heat until I reach my mash temperature, mixing the grains every now and again, turn off the heat and wait 90 minutes (I'm sure the conversion happens way before that, but I give it 90 minutes anyway).
  • I mash out, remove the grains and proceed to the boil.

This process allow me to more precisely control the mash temperature (heating the water above the mash temperature and adding the grains has always given me mixed results).

Given that enzymes are denatured when a certain temperature is reached, my mash goes through all the 'rests' until reaching the starch conversion rest at my target mash temperature. The heating process take around 30-40 min.

Any drawbacks in doing this?

  • 1
    As Franklin pointed out 90 minutes seems to be excessive with modern grains - there are lot of enzymes in them. OTOH, with the grains being in a bag there is probably a lot more time needed for heat to get into the bag, which would slow the process down. You could play around with the timing, but if the beer is good, the method is good.
    – Pepi
    Mar 22, 2015 at 1:55

2 Answers 2


Assuming you shoot for a saccharification rest around 65°C, the mash is heating up between ~1.4 and 1.8°C per minute. You'd make it through the 45-55° glucanase/protease range in ~5-7 minutes. I can't see this having a real effect on the wort composition, and I can't think of any other reason this technique would really make a difference. I'd say you'll be fine doing this.

And on the topic of saving time, I agree with you about the 90 minute mash being overkill. For virtually all base malts, it is.

  • Could a longer heating time have any adverse effect? What would a longer time spent on the glucanase / protease range cause, considering I'm using 'modern malts'? Would I see more break? Would I see changes in mouth feel? Mar 26, 2015 at 10:17
  • 2
    I think it would thin out the beer, and maybe this should a separate question?
    – Pepi
    Mar 26, 2015 at 11:07
  • I doubt it. Proteolytic activity in well modified malts is virtually negligible in all but the whackiest mash scenarios. Mar 26, 2015 at 16:21

I've been doing basically what you're doing for at least a year now. I'm not an award winning brewer by any means, but heating the water and grains together has worked just fine for me.

Agreed on the 90 minute mash being unnecessary. 60 minute mashes are also not needed, and if you really want to save time look into doing iodine tests on your wort.

  • The iodine test is a good tool, but it should be used cautiously. All it tells you is that the starch has been degraded to dextrins of or below a certain size. If you raise the temperature significantly right after reaching iodine-normalcy you could limit or effectively stop continuing β-amylase activity that might otherwise yield a more fermentable wort (but won't change the iodine test results). Mar 28, 2015 at 2:21
  • That's a good point. Mar 28, 2015 at 2:31

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