Low ABV due to over filling fermenter?

Brewer's Friend 728
Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
jono1492

jono1492

Well-Known Member
Joined
Jan 5, 2013
Messages
59
Reaction score
1
Location
Perth
Hey guys, I've brewed a few partial mashes thus far and they all seem to have low ABV. I'm not too fussed, but I would like to know where I'm going wrong and I have a feeling I'm over filling my fermenter, could this cause low ABV and what's a good way to calculate how much to fill my fermenter?

Btw, my last batch was a chocolate stout that only had an OG of 1.032 and finished up at 1.012, and I generally top to 21 litres(5.54gal)

Cheers!
 
Depends on your recipe and your mashing temps. If you didn't hit good temps or stir enough during mashing, you may have lower than expected efficiency.
 
Stirring the mash def helps get the grains evenly soaked. It'll raise your efficiency & thus,your OG. I have plastic fermenters with graduations on them to tell how much to top off to for total recipe volume. I also strain all going into the fermenter to aerate it & get less trub at racking time.
 
jono1492 said:
Hey guys, I've brewed a few partial mashes thus far and they all seem to have low ABV. I'm not too fussed, but I would like to know where I'm going wrong and I have a feeling I'm over filling my fermenter, could this cause low ABV and what's a good way to calculate how much to fill my fermenter?

Btw, my last batch was a chocolate stout that only had an OG of 1.032 and finished up at 1.012, and I generally top to 21 litres(5.54gal)

Cheers!
Click to expand...

Hmmm....that is pretty low. As the other guys have said you should try to increase your efficiency with your grain and you could also keep some extra DME around in case you need to bump up your fermentables.

Rick
 
Are you just blindly filling your fermenter up to 5.5 gals, or are you paying attention to your target OG and adding enough water to hit your target? If you are just blindly filling it up to 5.5 gals, then you are probably just watering down your beer. You need to calculate your brewhouse efficiency, and compare it to the brewhouse efficiency of the recipes you are using and adjust your base malt bill accordingly.
 
jono1492 said:
Btw, my last batch was a chocolate stout that only had an OG of 1.032 and finished up at 1.012, and I generally top to 21 litres(5.54gal)
Click to expand...

are you taking readings after you top it up? if so, your readings likely aren't accurate due to the difficulty of mixing water & wort evenly. in the future, take readings before topping and adjust as needed.
 
When you do a partial mash, do you also do a partial boil and the top off the fermenter? If so I would expect your OG to be very close to what was predicted but your reading was low due to insufficient mixing of the wort with the top off water.
 
Either low mash efficiency or not mixing wort & top off well. And it isn't that hard to mix wort with top off. It just doesn't do it well on it's own. I pour all through a fine mesh strainer in a circular motion so it comes out the bottom of the strainer like rain. Aerates well & helps mix the two. Then I use a plastic paddle to stir roughly for 5 minutes straight. I get accurate readings this way.
 
unionrdr said:
Either low mash efficiency or not mixing wort & top off well. And it isn't that hard to mix wort with top off. It just doesn't do it well on it's own. I pour all through a fine mesh strainer in a circular motion so it comes out the bottom of the strainer like rain. Aerates well & helps mix the two. Then I use a plastic paddle to stir roughly for 5 minutes straight. I get accurate readings this way.
Click to expand...

+1. Never had an issue mixing by stirring, it just doesn't do the work for you like when you add priming sugar.
 
unionrdr said:
Aerates well & helps mix the two. Then I use a plastic paddle to stir roughly for 5 minutes straight. I get accurate readings this way.
Click to expand...

freisste said:
+1. Never had an issue mixing by stirring, it just doesn't do the work for you like when you add priming sugar.
Click to expand...

how do you know its 100% accurate? im sure its close, but unless you're just using known amounts, i.e extract & sugars, its impossible to be sure once you top off. you can't just assume your efficiency will always be exactly the same
 
Because the OG is/was within the expected range. Not that hard. I've done it over many brews & that's the one thing that's consistent. If you've got a better way,we're all ears...
 
unionrdr said:
Because the OG is/was within the expected range. Not that hard. I've done it over many brews & that's the one thing that's consistent. If you've got a better way,we're all ears...
Click to expand...

key word there is range. a range is not an exact value, thus not possible to be 100% accurate. in any case, you're mixing it alot to get within said range, im betting the OP didn't. as i previously stated, the most accurate way is to measure it before topping, and then adjust as necessary. math don't lie

OG2 = OG1*Vol1/Vol2
 
One had a range of 1.042-1.046,I hit it at 1.044 as an example. Beyond that,I know I can get within range with my process at top up. But yeah,it seems like the op didn't get it mixed well at the least.
What you're doing is top off to projected gravity. That's fine,but my way works for me at recipe volume. It's just how I learned to get there.
 
It would seem I am blindly filling it up. How do I calculate efficiency?

So, just to clarify, I should be taking a reading before I top off, then add top off water until I get the desired OG?

reverendj1 said:
Are you just blindly filling your fermenter up to 5.5 gals, or are you paying attention to your target OG and adding enough water to hit your target? If you are just blindly filling it up to 5.5 gals, then you are probably just watering down your beer. You need to calculate your brewhouse efficiency, and compare it to the brewhouse efficiency of the recipes you are using and adjust your base malt bill accordingly.
Click to expand...
 
Calculate brew house efficiency of the partial mash using the post mash volume, specific gravity, and Potential points for the grains. I use the calculator on the brewers friend.

Unless you have >70% efficiency or add extra DME you will never hit your target OG while topping off to 5.5 gal on a 5 gal batch.

Recipes scale with volume so you need 10% more fermentables for 5.5 gal.
 
Also, how crucial is it to crack the grain when partial mashing? Because if it's relatively important, I may have just answered my own question. :s
 
jCOSbrew said:
Calculate brew house efficiency of the partial mash using the post mash volume, specific gravity, and Potential points for the grains. I use the calculator on the brewers friend.

Unless you have >70% efficiency or add extra DME you will never hit your target OG while topping off to 5.5 gal on a 5 gal batch.

Recipes scale with volume so you need 10% more fermentables for 5.5 gal.
Click to expand...

Sweet, thanks for that! I'm really glad I joined this forum, forever learning and on the way to better beer! Haha
 
jono1492 said:
Sweet as. So if I'm buying un- cracked grain, what's a good process/technique for getting a good crack? And how cracked are we talking here?
Click to expand...

Check out this link

That thread should give you a good idea of the grain crush you need and a good, cheap, way to go about it.

If you are doing BIAB you can go for a really fine crush where you'll have a bit of flour in the mix. If you are doing multi vessel AG you're better off going for a slightly more coarse crush, leaving the husks more intact for filtering the grain bed.
 
Ogri said:
Check out this link

That thread should give you a good idea of the grain crush you need and a good, cheap, way to go about it.

If you are doing BIAB you can go for a really fine crush where you'll have a bit of flour in the mix. If you are doing multi vessel AG you're better off going for a slightly more coarse crush, leaving the husks more intact for filtering the grain bed.
Click to expand...

Cool, cheers. And mind my ignorance, BIAB is?
 
Are you buying your grain from a Homebrew shop? They should be able to mill it (crush it) for you. I thought you Aussies invented BIAB?! Regardless, check out the links that have been posted and have fun!
 
MyNameIsPaul said:
Are you buying your grain from a Homebrew shop? They should be able to mill it (crush it) for you. I thought you Aussies invented BIAB?! Regardless, check out the links that have been posted and have fun!
Click to expand...

Haha, I dunno. Did we? And yeah I am getting it from a homebrew shop, so next time I'll see if they can mill it.

Cheers mate
 

Similar threads

Gabriel Sayegh
How do folks calculate ABV after a step feed with volume change?
Replies
12
Views
513
MaxStout
MaxStout
beervoid
Refractometer reading very different from Hydrometer, fermenting wort
Replies
20
Views
2K
jschein
jschein
D
Restart fermentation to fix my mead?
Replies
9
Views
589
Raptor99
Raptor99
Luxy
Fermentation...
Replies
6
Views
430
Rish
R
J
Non-alcoholic homebrew - buzzed feeling?
Replies
7
Views
620
mashdar
mashdar
Yakima 300

Latest posts

Back
Top