Missing Target Gravity

[SamInNJ]

I've done probably 4 or so 5.5 gallon BIAB brew days so far and my starting gravity is coming in consistently a few points lower than I'm estimating on BeerSmith.

I noticed my volume was a bit high on the last batch, so today I took care to make sure that after my mash I had about 6.5 gallons (I had a little extra and boiled a bit before starting my timer to get it down to 6.5). The brew went off without a hitch and I ended up with exactly 5.5 gallons into the fermenter as expected, but was 4-5 points low on the gravity (it was supposed to be 1.040, measured about 1.036).

The recipe is the popular blonde ale recipe from elsewhere in the forums. For reference:
7lb US 2 row
12oz cara-pils
8oz cara 10
8oz vienna
55m 0.25oz centennial
35m 0.25oz centennial
20m 0.25oz cascade
5m 0.25oz cascade

Additionally per bru'n water -> added 0.25g/gal of calcium chloride and 0.25g/gal of gypsum. Also added 5oz of acid malt for PH.

Process:
All of my grains were doubled crushed. I mashed in at 150. 60 minutes later the temp was at 148, I slowly raised the temp to 168 and removed the bag and discarded the grains (did not squeeze as my volume was already sufficient).

Everything seems to have gone without a hitch tho the gravity is low

I thought maybe I would get a higher gravity if I squeezed the bag, but I can't imagine it would account for 4-5 points. Any thoughts on how I can make this up?

My thoughts are on my next batch to use a little less water in the mash (used 7.5 gallons this time, probably use 7 next time) and squeeze the bag a ton to make sure I get 6.5 to start the boil. I was also thinking of buying iodine to test that conversion is complete, or mashing longer to ensure that.

 

[jrowland74]

I'm no expert on BIAB, but it's my understanding that, along with a finer crush, you should raise your grain bill by about 10%.

 

[jlinz]

I sometimes have the same issue, though not on every batch. I will bump up the grain a bit, as has been suggested, or I add a bit of dme, sometimes light brown sugar, before or sometimes after the boil just to get things where I want them, or I sometimes just let it roll as is. Poorer efficiency comes with the territory, but you can't beat the convenience of biab.

 

[nick_a]

Hi Sam,

What is your expected brewhouse efficiency in beersmith?

What is your water:grist ratio during your mash?

What is your mash pH after additions?

In absence of more info, my knee jerk suggestions would be the following:

Mash for at least 75 minutes, and make sure your thermometer is calibrated

Water:grist ratio should at least be 2 qt/lb

Always squeeze. If needed, withhold strike water volume to use for a "sparge" after mashout. You can always boil for a bit longer to hit your target volume, but my gut suspicion is that there's a lot of wort still tied up with your grain bag, which is messing with your target OG.

 

[SamInNJ]

Efficiency is 70%
PH was 5.3 (bru'n water calculated)
Water to grist was about 3qt/lb (full volume mash)

Will bring my water down to 7 gal from 7.5 for the mash and squeeze like crazy to et my volume and see how that works next time.

Should I lower my brew house efficiency in beersmith?

 

[TimmyWit]

Efficiency is 70%

Should I lower my brew house efficiency in beersmith?

Yes, take your last batch and lower the eff until your estimated OG is equal to what your actual OG was. Build your next batch with the lower eff in Beersmith and you should nail it.

 

[JosephN]

Yes, take your last batch and lower the eff until your estimated OG is equal to what your actual OG was. Build your next batch with the lower eff in Beersmith and you should nail it.

That is exactly what I do.

I started out with 60-65% efficiency until I got my own mill and I get at least 70-84% now, so when formulating my recipes I use the current lower 70% as my base. When I get finished I usually end up rising a specific batch % up 4-10 points.

 

[jlinz]

Yes, take your last batch and lower the eff until your estimated OG is equal to what your actual OG was. Build your next batch with the lower eff in Beersmith and you should nail it.

Ah, excellent! Hadn't thought of this.

 

[TexasWine]

removed the bag and discarded the grains (did not squeeze as my volume was already sufficient).

Everything seems to have gone without a hitch tho the gravity is low

I thought maybe I would get a higher gravity if I squeezed the bag, but I can't imagine it would account for 4-5 points. Any thoughts on how I can make this up?

My thoughts are on my next batch to use a little less water in the mash (used 7.5 gallons this time, probably use 7 next time) and squeeze the bag a ton to make sure I get 6.5 to start the boil. I was also thinking of buying iodine to test that conversion is complete, or mashing longer to ensure that.

Depending on how much wort you left in your grain, you could easily make up 4-5 points. That's most likely why you ended up short. You should have drained as much as possible from your bag, via squeezing it or gravity. You would have been long on volume but a longer boil would have taken care of that extra water.

After a few brew days you'll get your system dialed in. I build my recipes on 80% brew house efficiency and always get 80-86%. Don't let anyone tell you BIAB sufferers from lower efficiency.

 

[IslandLizard]

+1^
Finer crush, squeeze and dunk sparge. Get those sugars out of that grain. Using BIAB you should get at least 80% efficiency, all the way up to 90%.

 

[pricelessbrewing]

I'm no expert on BIAB, but it's my understanding that, along with a finer crush, you should raise your grain bill by about 10%.

UGGGGH no.

BIAB typical mash efficiency is 72-75%. Not much different from a mash tun batch sparger.

There's a pretty thorough write up the different types of efficiency, and what how to calculate each one on my blog at http://pricelessbrewing.github.io/methods/Efficiency

The two biggest things to not how to hit your target OG (ie mash efficiency) is to determine your conversion (how well the mash went) and lauter (how well your sparge went) efficiencies. Without those, it's hard to predict how a different recipe will affect your mash efficiency.

 

[doug293cz]

Used my simulator and your grain bill, volumes, and OG to estimate your conversion and lauter efficiencies. Lauter efficiency worked out to about 81%, which isn't too bad. It was dragged down some by your high (for BIAB) grain absorption of about 0.125 gal/lb. With good bag draining and/or squeezing BIABers can get grain absorption in the 0.06 - 0.09 gal/lb range, and improve their lauter efficiency.

A bigger problem for you is your conversion efficiency, which was only about 79%. Homebrewers should be able to regularly achieve better than 95% conversion efficiency. Finer crush usually gives the biggest bang for the buck to increase conversion efficiency. Gelatinization works from the surface of grits towards the center, so finer grits can gelatinize and convert faster. Longer mash times can also improve conversion efficiency, but may be limited if the enzymes denature before conversion is completed.

Rather than using iodine to measure conversion completion, I recommend monitoring the mash SG as described by Kai Troester here.

Your mash efficiency (conversion efficiency times lauter efficiency) was about 64%.

If you can get your conversion efficiency up to 95% and your grain absorption down to 0.08 gal/lb, your lauter efficiency would improve to about 84% and your mash efficiency to about 80%, for a full volume, no sparge mash.

Brew on

 

[pricelessbrewing]

Rather than using iodine to measure conversion completion, I recommend monitoring the mash SG as described by Kai Troester here.

Brew on

Regarding mash readings vs first running readings. I've had a number of brewers comment on this so far, but was wondering if you've experienced it. I've been hearing lately that the gravity before and after squeezing has been slightly different, 4-5 points, from a number of brewers. I'm not entirely sure if it's due to differences in the actual gravity or if it's just a case of not stirring adequately before pulling the bag.

Thoughts?

 

[doug293cz]

Regarding mash readings vs first running readings. I've had a number of brewers comment on this so far, but was wondering if you've experienced it. I've been hearing lately that the gravity before and after squeezing has been slightly different, 4-5 points, from a number of brewers. I'm not entirely sure if it's due to differences in the actual gravity or if it's just a case of not stirring adequately before pulling the bag.

Thoughts?

The times I've measured, the first runnings SG and squeezed wort SG were within 1 point (0.001.) I agree that lack of adequate stirring is a likely cause. Stirring needs to be sufficient to get uniform SG throughout the entire mash. Also, if conversion isn't complete when the bag is pulled, the squeezed wort SG could benefit from some additional conversion taking place.

Brew on

 

[pricelessbrewing]

Alright that was my initial thought as well, as I haven't experienced it I wasn't sure what it might be beyond speculating.