Low OG, brewing at high altitude

[rockymtnbrewer]

Today I brewed my third AG beer, a simple SMaSH. 10 lbs Maris Otter, single infusion mash at 154 degrees, 1 hour boil. I had a preboil volume of 7.5 gallons, preboil gravity was 1.041 (corrected for temperature), giving me a brewhouse efficiency of over 80%, according to brewersfriend. When I plug my recipe in brewersfriend's recipe builder it gives an expected OG of 1.055. My gravity reading after boiling was 1.049 (again, corrected for temperature). Why the low OG?

Additional info: I brew at about 5,100 ft elevation. Water boils at about 203 degrees. I know it takes longer to cook at elevation, should I just boil longer? Add more grain? My volume after boiling is right where I want it. Any ideas?

 

[rockymtnbrewer]

To add a little more info, this happened to my 2 previous brews. First thing I thought was grain crush so this time I had my LHBS adjust the mill to give me a better crush, but same results.

 

[CRoth36]

Grind or pH is what I would check first. My brew at 7,200 and don't run into any problems that are due elevation.

 

[rockymtnbrewer]

Grind or pH is what I would check first. My brew at 7,200 and don't run into any problems that are due elevation.

Water chemistry is something I didn't think of. I use Eldorado Natural Spring Water. They report a pH of 7.33. Correct me if I'm wrong but I was under the impression that water pH isn't too important, it's the mash pH that is and it's determined by the other ions in the water combined with you grain bill. If water pH was a factor wouldn't I get varied results with my previous brews? I used the same water but very different grains.

 

[chickypad]

By the numbers looks like your post boil volume should have been about 6.25 gals. Is that what you got?

 

[rockymtnbrewer]

By the numbers looks like your post boil volume should have been about 6.25 gals. Is that what you got?

Probably closer to 6.5. Maybe about 6.4?

 

[chickypad]

So looks fine, and high efficiency. If you're wondering why it doesn't match the brewer's friend estimate of 1.055 I assume that was set for 5 gals.

 

[rockymtnbrewer]

So looks fine, and high efficiency. If you're wondering why it doesn't match the brewer's friend estimate of 1.055 I assume that was set for 5 gals.

It is automatically set to 5.5 gal when I start. Maybe I'll just add more base grain on my next batch or maybe do a 90 min mash, I'm stumped.

 

[MindenMan]

Even though I "technically" shouldn't need to do a 90 minute mash, in spite of all the other things I did including double grind my grains, my 60 minute mash beers all came in below predicted O.G.. I am back to 90 minutes and I don't have to "over sparge" to collect enough 1.020 wort to boil down to get the O.G. I want.

 

[chickypad]

It is automatically set to 5.5 gal when I start. Maybe I'll just add more base grain on my next batch or maybe do a 90 min mash, I'm stumped.

If the recipe is set for 5.5 gals and you are finishing with 6.4 gals it shouldn't be a surprise that your gravity is lower than the target. The batch size and efficiency are things that you need to set in the calculator to match your system, if you go with the defaults you're probably never going to hit the numbers. There's a couple different ways to set your efficiency - I like to use the mash or kettle efficiency and target the volume and gravity in the kettle at the end of the boil. I find this easier to reproduce than brewhouse efficiency - i.e. the packaged batch size after trub and fermenter losses. Check Brewer's friend site but I think it is calculating the post boil efficiency - hence your discrepancy.

 

[botigol]

If the recipe is set for 5.5 gals and you are finishing with 6.4 gals it shouldn't be a surprise that your gravity is lower than the target.

Exactly! Running a quick calculation through a Pearson's square shows an extra gallon affecting gravity by about 0.008.

 

[rockymtnbrewer]

Exactly! Running a quick calculation through a Pearson's square shows an extra gallon affecting gravity by about 0.008.

When draining your boil kettle do you drain completely? The .75 - 1 gallon I have been leaving is very sludgey.

 

[botigol]

Personally, I drain it, but a lot of people only take the clear liquid. Either way seems to work fine, just a matter of how you and your system work best.

How much are you putting into your fermenter?

 

[rockymtnbrewer]

Personally, I drain it, but a lot of people only take the clear liquid. Either way seems to work fine, just a matter of how you and your system work best.

How much are you putting into your fermenter?

5.5 gallons in a 6 gallon carboy

 

[botigol]

Adding grain will solve the issue; offhand you're looking at an additional pound per batch.

A longer mash should improve your mash efficiency, but maybe you just need to stir more during the 60 mins. In the same vein, you could dough-in at 100-104F for 15-20 mins, which would also increase mash efficiency, but unless you can direct fire your mash tun, getting up to saccharification temp in a timely manner can be tricky.

You could try completely draining your kettle, which would require more boiling to reduce the wort volume (I would try 6 gals), because the trub will compact more in the fermenter than in the kettle, but then also require a larger fermenter to accommodate the larger volume into the fermenter.

Mash pH could be part of this as well. Unless you have brewed a porter or stout, even with different grains, the mash pH could have been high.

Even though your LHBS double-crushed this last batch for you, it is possible that it wasn't enough.

What is the liquid to grist ratio in your mash?

 

[rockymtnbrewer]

Adding grain will solve the issue; offhand you're looking at an additional pound per batch.

A longer mash should improve your mash efficiency, but maybe you just need to stir more during the 60 mins. In the same vein, you could dough-in at 100-104F for 15-20 mins, which would also increase mash efficiency, but unless you can direct fire your mash tun, getting up to saccharification temp in a timely manner can be tricky.

You could try completely draining your kettle, which would require more boiling to reduce the wort volume (I would try 6 gals), because the trub will compact more in the fermenter than in the kettle, but then also require a larger fermenter to accommodate the larger volume into the fermenter.

Mash pH could be part of this as well. Unless you have brewed a porter or stout, even with different grains, the mash pH could have been high.

Even though your LHBS double-crushed this last batch for you, it is possible that it wasn't enough.

What is the liquid to grist ratio in your mash?

I use a 10 gallon igloo cooler for mash tun so I think I'll stick with a single infusion mash.
Next batch I will add a pound extra base and stir the hell out of it.
I use 1.33 qt/lb
Thank you for your help!

 

[botigol]

You're welcome! If you'll take another $0.02 from me, I would start with increasing your liquid/grist ratio to 1.5 qt/lb and stirring more. Then pull a sample at 60 mins for SG. If it is low, you could then let the mash go longer (75 and then 90 if necessary) to see if that will take care of it. This way you are hitting two to three 'operational' factors without laying out more money.

 

[chickypad]

I'm a dump everything in the fermenter kind of gal, I find that I have less total losses this way, but I know some folks don't like all that trub in their fermenters especially if harvesting yeast. Eiither way, the main thing is to dial your system in the way you want it and set the correct numbers in the calculator so you can hit your numbers reliably. Honestly your mash efficiency looks fine, I think you're in the high 80's if my quick calcs are right, so I don't know that you need to do anything with your actual process unless you want to.

 

[CRoth36]

You want your mash pH around 5.2. However you want you post boiled wort to be around 5 so that takes adjusting your sparge pH which we usually try to keep around 5.6 or so. I forgot your original question but think it was something about efficiency. Not sure if any of this actually helps.