Good stuff Al

. Glad the last post made some sense and sorry I couldn't get back to you sooner.
It's also great that the 'shop' posts made some sense and that you now have a second 19 L pot. I am assuming that this second kettle is exactly the same as the first? If so, the next question is can you fit both these 19 L kettles on your stove and bring them to the boil? If so, this actually opens up several more possibilities.
For example, if you make a second bag, you can actually just do a 'full volume shop' brew with the only difference being that you are using your kettle 'split in half' if that makes sense. To set the BIABacus up to do this, we would double the existing evaporation rate estimate of 3.03 L/hr to 6.06 L/Hr and set this in Section X. In section B, we just need to double the Kettle Height. The other alternative is to just leave it as is and just remember to double the relevant numbers/weights in your head. (Hope I haven't made that too confusing.)
The end result is that, with your two 19 L kettles, you can actually brew enough DSGA to get 19 L into a fermentor using no dilutions.
You actually don't even need a second bag to do the above. You could mash in your first kettle for say 20 minutes and then move the bag to your second kettle for the next 60 minutes. Boil the first kettle for 90 minutes with your bittering hops. Boil the second one for just 60 minutes and do your flavour and aroma hops in that one. But, this sort of mucking around is tending on the silly side
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There are hundreds of variations but as soon as they vary from full volume, they all get tricky in some way. So, I think the first choice to make is, "Do you want to make a second bag and just do two simultaneous smaller batches to make a standard batch or would you only like to use one kettle and bag for the actual boil?"
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I'm not sure whether to write more now as I might just make things more confusing. Probably one of the most important points to get for now is that the second pot you bought, can gain you a lot of volume if it is actually used as a second BIAB kettle. In other words, if you have a second burner and bag for it.
Imagine though if you don't... The second pot can only be used to gain the amount of liquor retained by the grain when the bag is pulled from the first kettle which is never that much unless you are doing a really high gravity brew.
To see what I mean here Al, in Section W, type 5 L into 'Water Used in a Sparge' and 5 L to 'Water Added During the Boil'. We have no serious red warnings appearing. Look at your total grain bill requirement (2950 g) and then move that 5 L from 'Water Used in a Sparge' to 'Water Added Before the Boil'. All that changes is you will now need 3299 grams of grain. So, is the mucking around with sparging using the second pot worth the savings of that approx 10% of grain?
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In contrast to the above, as I mentioned above, if you use the second pot as a kettle, you can actually do no dilutions and get 19 L into a fermentor rather than the 15 L above that requires a lot of dilution. In fact, using the same dilution amounts as above would actually allow you to get about 30 L into a fermentor using the two 'mini' kettles.
To check this, you can also use your existing BIABacus file. In Section B, to check the no dilutions, type in 9.5 L for VIF (half of 19 L). For the dilutions, type in the 5 and 5 into Section W and then in Section B, type in 15 L (half of 30 L).
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Sorry there is so much to take in above. I think I have actually wrecked this post by not posting it in stages. That's the problem with any full-volume variation (maxi-BIAB). The possibilities
are really infinite.
The main point to get across though in this post was hopefully getting you to see that using your second pot as a sparging pot versus using it as an actual kettle really is a massive difference.
PP
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