The issue of high gravity beers is not one of single vessel all-grain brewing (SVAG - pure BIAB) versus multi vessel all-grain brewing (MVAG - traditional all-grain); it's a completely different issue, the issue being that you are trying to wash a large amount of grain in a small amount of water.
If you haven't read up on "dirty jeans" on this site, try and find a few posts on that. Pretty sure I've written some very detailed ones on that within the last six months. Once you've read and understood the "dirty jeans" analogy, then you'll know the following...
The effectiveness with which you can wash grain (get the sugars from them into your water) mainly depends on the amount of grain versus the amount you wash with. Other things that effect this are agitation, temperature and pH. All of these things, regardless of the all-grain system you use, can be optomised. In other words, the brewer, regardless of system, can control agitation, temperature and pH. (The SVAG brewer does havbe one advantage though, no vessel "dead-space" losses).
Reiterating Mash (and Sparging)
I like that term aamcle
however there is only one practical instance for it and that is when your kettle is too small for what you are demanding (that's what mally mentioned above.) For example...
If my high gravity recipe demanded 10kgs of grain with a Total Water Needed (TWN - Section K of BIABacus) of 35L but my kettle was only 40L, then I have a problem because the grain and all the water won't fit in my kettle in one hit. If my kettle was big enough though, and I could add the everything, there is no other method that will get a better result than doing that.
So, when people have a small kettle, they are forced to compromise: you can re-iterate the mash, sparge the mash or a combination. Those things though, will give you a better end result than if your ketttle was big enough to take everything in one hit.
So, what are the real answers for a high gravity beer?
There are only two solutions to brewing a high gravity beer:
1. Add some type of sugar: You'll notice that most high gravity beers do have some sort of sugar in the recipe. The reason for this is because the only other alternative is...
2. Increase Evaporation During the Boil (usually by extending boil time): Occasionally you'll find a high gravity beer without added sugar, but, with a very long boil time, 3 hours or so. Why? Because, extending the boil time is the simplest way of increasing evaporation and, the more evaporation you have, the more concentrated your wort becomes. (The only other way I can think of for a home brewer to increase evaporation would be to have a fan blowing on top of the wort as it boils.)
The Law of Diminishing Returns
This is another point, whilst relevant to any gravity brew, it is particularly relevant to high-gravity all-grain brewing. Two examples of this law are...
- The longer you mash for, the better extraction you'll get however, the sugar extracted per minute diminishes and will eventually equal zero.
- You can get super high gravity as long as you evaporate enough. For example, you could boil your wort down to a syrup.
Finally, just imagine...
Let's say you had a kettle and a recirculating system and that this recirculating system could evenly suck from the bottom of your mash tun (or kettle in the case of SVAG) and sprinkle it evenly over the top of your mash.
Let's say you were re-circulating 40L of water though 10kg of crushed grain, over and over, for 24 hours.
Now imagine you had the same set-up but you only added 5kg of grain, ran your system for 12 hours then swapped the 5kg of grain with a fresh 5kg and ran the system for another 12 hours.
Which method would result in the "sweet liquor" with the highest gravity?
PP
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