Contrary to home brewing lore, the well respected Dennis E Briggs found that thin mashes do not affect the fermentability of wort. One high quality information source has written here that thinner mashes, "perform better and allow for better extraction of the grain."
Brewing chemistry is often contradictory so having a few ways of looking at the same subject may help some brewers. Dan Walker (ThirstyBoy) kindly provided the following to BIABrewer...
Firstly, let’s look at whether our wort will be too sweet or too dry using such a thin mash.
Beta amalayse enzymes are heat liable. ie: they snuff it fairly quickly at higher temperatures. One of the reasons why they dont snuff it in a normal mash tun, is that there is a buffering stabilising effect when they are in an environment which has a high concentration of their substrate. ie: a thick mash.
Mashing theory tells us that Beta Amalayse is responsible for making short fermentable sugars and if you want dry beer, you need to promote the Beta Amalayse action over the alpha amalayse (which produces longer chained dextrins)
If you have a very thin mash – you lose the buffering effect of the high substrate concentration and the enzymes themselves work more slowly in the more dilute solution. So what conclusions can you draw??
Obviously that the very thin mashes of BIAB will mean that the Beta Amalayse enzymes will not get a chance to work before they are denatured, and the only things left to convert the starch will be alpha amalayse (which produces dextrins remember) so therefore BIAB beers will be too unfermentable and sweet. Right??
Not so much! This is a case of a little knowledge being dangerous. Mashing theory is quite a bit more complicated than that and there are a lot of different things going on in there. There is substrate inhibition, product inhibition, gelatinisation and liquefaction rates and percentages. And, the fact that the enzymes don’t work alone but act on each other’s products. Great swathes of inter-acting factors, all of which add up to the fact that given a decently diastatic malt and a not stupid proportion of unmalted adjunct – there is not a hell of a lot of difference between the fermentability of a wort mashed at a 3L/kg ratio and one mashed at 7:1. Sure, you might run out of luck at higher than that... but we don’t need to go there so it doesn't matter. Will there be a difference between a beer brewed with a genuinely thick mash (less than 2:1) and one brewed at 6 or 7:1? Probably, but certainly nothing that can’t be completely compensated for by tweaking your rest temperatures a little.
Just use the temperature recommended for “normal” mashing and it will be fine.
But what about a too dry wort?
It is simply the same argument in reverse. Home brewers “know” that a thinner mash will lead to a more fermentable beer. You will see words roughly to that effect in Palmer and Fix and probably Noonan too. So obviously an ultra thin mash like BIAB will lead to a very fermentable and thus overly dry beer. Right???
The trouble is, those texts refer to some quite specific things, not to a general effect that can be endlessly extrapolated. There is (possibly) a minor difference in the achievable limit attenuation between a beer brewed at a low L:G (thick, less than 2:1) and one brewed at 3 or 4:1. But there isn't really much difference between medium L:G ratios and high ones, and there is basically no difference between high and very high. Once you get to about 2.8:1 – it’s all pretty much the same. Any minor difference between a BIAB mash and a traditional one is, once again, more than controllable via mash temperature.
Credits: Dan Walker (ThirstyBoy) provided all the information in the latter part of this post. Any mistakes due to editing are entireley the fault of BIABrewer.
Post #1 made 9 years ago
Last edited by BIABrewer on 22 Feb 2010, 20:40, edited 2 times in total.
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