10 Gallon Biab split into 2

Ive searched the forums and can't seem to find an answer to this question. I have a 15 gallon brew kettle, and it is big enough to do a full 10 gallon boil, but it's not big enough to do a full 10 gallon biab mash. So what I thought I could do was split it into two. Take half the grains, do my normal 5 gallon biab for 90 minutes, then put that wort into a bucket/extra kettle, then do another 5 gallon mash. Once that's complete add the original wort to the mix and do my normal 90 minute boil for the full 12+ gallons that I have. My question is, will this hurt/affect the original wort sitting in a brew pot for 90+ minutes not receiving heat ?

No answer for you but I am subbing because I was wondering the same thing earlier today!

I cannot imagine there would be a problem. I would use the iodine method to make sure that the sugars are fully converted in both batches. Then take refracto readings for sanity. If pre-boil readings are real close you should be good to go.

What BIAB method are you using? Filling the BK with the total water for the brew?
If you are you could try mashing with 1.25 - 1.5 qt/lb and then rinsing the grain once you remove the bag till you have your required volume.

I wondered this myself a few times.

I usually use ~7.5 gallons of water for 5 gallons of final wort. You wouldn't boil as much off so you wouldn't need 15g total water to end with 10g of wort.... right?

What if you figured out how much total water you needed and put it in the kettle, then mashed half the grain bill for 90 min. Reheated and mashed the other half in the same water for 90 min? I dunno just an idea.

I am curious as to what you end up doing and how it works out.

@gunner65 TY for the iodine test I will do that to make sure its good to go, but with a 60 minute mash @ 152ish and then raise temp to 168 for mash out for 20 minutes I should have pretty good conversion right ?

@Mattd2 I do the full amount of water with my biab, so I would do a 5 gallon batch with 8 gallons or so for my IPA's

@Gunner...So the original wort, it won't hurt it if it chills for like an hour and a half prior to bringing it to boil ?

whiskeyjack said:

@Mattd2 I do the full amount of water with my biab, so I would do a 5 gallon batch with 8 gallons or so for my IPA's

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Yeah, so what I was talking about is more of a "traditional" method of mash then sparge so that you wouldn't need the full water and the grain to be in the pot all at once. Basically mash with the volume of water you would in the non-BIAB method, then lift the bag out and rinse with water until you hit your preboil volume. This is how I do it (but for only 3 gallon batches), so one thing that might be a pain is holding the bag while rinsing. But what I have just started to do is put the bag in another bucket after lifting it out of the pot (you could use your fermenter if you use buckets not carboys) and doing a batch sparge in there and giving it a good stir then dumping it into the pot. I did 2x sparges like this on my last batch. I read somewhere on here that the temperature of the sparge water is not all that critical for rinsing the grains out (if you want to get a good mash out to stop enzymes temp is critical).

whiskeyjack said:

@Gunner...So the original wort, it won't hurt it if it chills for like an hour and a half prior to bringing it to boil ?

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I know of several posts where the mention of mashing and sparging one day then boiling the next. Maybe someone of more experience could chime in. I really cannot see how chilled wort that is re-heated could have issues. You could mash into a cooler or other insulated vessel which would probably keep the temp up over the next batch time.

As for full conversion I only mentioned iodine for sanity checking YMMV.

What you do need to do is report back here with how everything goes so others can learn. I know I am interested. Good luck!

I'd just make it a partial mash and pick up some DME.

I don't know the answer to your question of the wort sitting and cooling for 90 minutes, but I don't see that it would be problematic.

Have you tried mashing your full grain bill in half of the total water volume, then drain wort to another container, heat/add other half of water volume to kettle, let sit for 10-15 minutes, then drain/lift bag, and combine the two different worts? This is basically a batch sparge process utilizing the bag as a portable false bottom. This will also save you 60-75 minutes by doing a sparge instead of two separate 90 minutes mashes. In other words, conduct one 90 minute mash followed by a bag sparge, rather than two separate 90 minutes biab's.

You wouldn't have a problem letting the runnings sit for another hour.

But what I'd suggest you do is do 8-9 gallon batches like I do. I can easily mash 16lbs of grain for an average-sized ale in my 15.5gal kettle no sparge or top-up, full volume BIAB and get high efficiencies and 9gal into fermenters. The biggest grain bill I've done is a 1.092 doppelbock that was, I think, 27lb of grain. I came out with about 8 gallons into fermenters with low 70% efficiency.

Thanks for all the input every one, I think I'll try what MrF says and kind of do a dunk sparge, save some time