Loosing efficiency with my 10g vs 5g BIAB

[strongarm]

I have had consistent success doing 5g BIAB batches hitting ~70% right where I expected. When I do a 10g batch I seem to get around 60%. After the mash I drain the bag and add to another pot with water at around 170. I usually leave it in for around 5-10 minutes then drain the bag again but with the 10g I had to transfer the grain into the second pot in batches since the pot wasn't big enough to take it all at once. I only let it sit for a minute before draining. I'm thinking by not letting the grain sit longer in the sparge water I lost some efficiency there? I'm not too worried about $ with my brews so maybe I can just add 10% more grain to the bill to make up for it in my 10g batches? Also my mash temps seem to be a 4-5degrees lower than I usually get with 10g batches. I think it's the extra time it takes to mash in or maybe the extra grain is causing the water temp to drop more? I guess I'm finding that I need to adjust my process for doing 10g batches over 5g. Any advise is appreciated.

 

[ArcLight]

>>also my mash temps seem to be a 4-5degrees lower than I usually get with 10g batches.

Thats a huge difference. With BIAB you need to really mix in your grain, and not have large pockets with very different temperatures.
You don't mention your mash temperature but 152 vs 157 makes a difference.

This part of your process needs to be mastered for consistency and to diagnose differences.




If you have a refractometer take the following readings:

1 - 5 gallon brew - after you pull the bag out of the main pot
2 - 5 gallon brew - after you pull the bag out of the second pot (the sparge pot)

This gives you a base line of what you expect form first and second running. Now do the same with the 10 gallon batch


3 - 10 gallon brew - after you pull the bag out of the main pot
4 - 10 gallon brew - after you pull the bag out of the second pot (the sparge pot)

See where the 10 gallon differs from the 5 gallon.

If there is a big difference between #2 and #4 then try letting the grain sit in the water for 5-10 minutes, not just 1 minute