BIAB-91% efficiency and lactose

[Sudstud]

Hello all, did my first BIAB last night and I have some questions about an apparently high efficiency.

Jamil's Triple x Stout- Recipe cut in half for 3 gallon batch (didn't want to screw up 5 gallons on my first attempt.)

5lbs Marris Otter
.33lb Crystal 80
.25lb pale chocolate
.5lb black patent
.5lb lactose added at 45min
.75oz east kent goldings @ beginning of boil

Recipe calls for pre boil gravity of 1.051 and post boil of 1.060, efficiency of 70%

My procedure:
Strike water-4 gallons at 161*
Mash Temp- 152* for 70 min
water loss to grains-1 liter
Pre boil volume 3.75 gallons
Pre boil gravity 1.054 (wort was mixed and cooled, hydrometer is tested and accurate)
60min boil
Post boil gravity 1.070
post boil volume 3 gallons

I did a mash out for 10 min @168* while stirring then squeezed the crap outta that bag. The grains were Northern Brewer's standard crush.

If I calculate my efficiency using the Brewers Friend calculator it comes to 91% pre boil and 94% post boil, I realize that the lactose will bump the post boil gravity, but I came out 10 full points above what the recipe called for!
I decided not to dilute it and just have a higher alcohol stout.

So, my questions for all the BIAB folks out there-
Is this a fluke?
Did I figure something wrong?
How should I adjust my procedure to get closer to what the recipe calls for? Right now all I really want is to learn to brew consistently.

Thanks all, this forum is great!

 

[PoppinCaps]

Using Beersmith, I'm getting 84% pre-boil and 87% post-boil. Depending on how efficient you were at rinsing the grains and the crush, that's certainly possible with BIAB (well, not a higher percentage of sugars post boil, but we can chalk that up to measuring error, etc). Nice! Do a bunch more batches and see if you consistently get this efficiency with the same process and similar recipes, and if so just scale back the recipe for your efficiency.

Not sure why the discrepancy from Beersmith to Brewers Friend, but I stopped using it for this reason. Figure I better just go with one even if it's wrong.

Also, I would double check that grain absorption somehow, maybe measure volumes in your kettle if you don't have a sightglass to calibrate. I get typically 0.12-.15gal/lb grain in a mash tun, and they're pretty dry (which would be around 3 liters for this recipe). Maybe if you squeeze the holy hell out of them you'd get lower, but probably not just 1 liter. That would explain the difference in pre/post boil efficiencies, I would think, if you're actually starting out with more than 3.75gal. Just a thought.

 

[Sudstud]

Thanks for the reply!

My plan is to do a couple more recipes and see if this will be consistent enough to do my calculations with.

As far as the different % of sugar pre boil and post boil, wouldn't the addition of lactose account for that? I took the pre boil before adding the lactose (it was added with 15 min left in the boil). Am I understanding that correctly?

I've seen a few people report a water loss of .06gallon/pound for BIAB which would put me at just over a liter, and yes, I squeezed the living crap out of it. Actually I put the bag in a steam basket over a bucket and pushed on it as hard as I could with a pot while I brought the rest of the wort to a boil.... I measured volume in my pot using a yardstick of sorts, 2" of water in my kettle=1 gallon so I have the stick marked to measure 1 quart increments. Not super accurate, but close enough for me...or maybe not The small amount of water loss surprised me too but I'm fairly certain its accurate because my 7.5gallon pot has a darker oxidation line at the 4 gallon mark (from all my test runs figuring boiloff) and I was 1/2" below that after squeezing the grains. After the boil, using the same method, I was at 3 gallons exactly.

Thanks for the suggestions, I will defiantly try to be more accurate with the water on the next batch to make doubly sure my method is right. I've used Beer Smith and iBrewmaster, I prefer iBrewmaster right now because with my limited knowledge its easier to understand. Just wish it had an actual efficiency calculator!

 

[PoppinCaps]

Yep, good catch, the lactose would account for the difference in pre-post. And it sounds like you've got the volumes and losses all figured out. Can't complain about 85-90%!