All-Brett finished at 1.002

Bottled an all-brett last night. Gravity 1.002. I was expecting it to be about 1.006-1.008. Is this normal?

It was a PM with 2 lbs 2-row, 2 lbs Munich, 0.65 lbs Acid, 0.5 lbs Flaked Oats, mashed at 148F. Plus 5 lbs Pale LME and 1 lb sugar. OG: 1.058 for 6.5 gallons.

Tasted pretty good.

I've been having a number of yeasts finish really low recently.

What kind of brett did you use?

B-Dub said:

What kind of brett did you use?

Click to expand...

Brett-B, WLP650. Used as the primary yeast. Thought it had finished at 4 weeks (it was clearing nicely and was at 1.008). I added some dry hops and it just started right up again.

Checked my notes. Last time I used it in a similar recipe, it went to 1.006.

sounds very very similar to a beer I just bottled
http://smokingbottle.wordpress.com/2011/02/15/a-duck-on-my-calendar/

Mine ended at 1.006 This was the lowest any of my all brett beers has ended, but also the first time I've used Brett B. So right now I am thinking that it is just this strain. Usually I expect my all brett beers to end around 1.010

It could also be that the reduced pH of the beer (from the acid malt) gives the Brett a big helping hand in the beginning and it can rip through the beer. I need to do a Brett B beer without a lowered pH to figure it out.

also, check your hydrometer. Mine is 4 points low. So when it reads 1.002 I know it is actually 1.006

A pound of sugar in a 1.058 beer along with a mash temp of 148 for your partial mash will get you a very dry beer no matter what yeast you use. Not that this is necessarily a bad thing.

oooh yeah.... I didn't see the 1lb of sugar.

Hydrometer is fine.

1 lb of sugar in 6.5 gallons is about .007 (or about 12%). So the malt portion of the OG would have been 1.051. Still 96% attenuation.

Calder said:

Hydrometer is fine.

1 lb of sugar in 6.5 gallons is about .007 (or about 12%). So the malt portion of the OG would have been 1.051. Still 96% attenuation.

Click to expand...

It doesn't exactly work that way. Alcohol is less dense than water. Just for fun I busted out my chemistry skills from the one class I took early in college and by my math the sugar takes your FG down an extra 3 points. So really you're looking at 90% app. attenuation (1.051 -> 1.005), which is still high, but not that surprising for brett, especially given the temp of the PM.

slowbie said:

It doesn't exactly work that way. Alcohol is less dense than water. Just for fun I busted out my chemistry skills from the one class I took early in college and by my math the sugar takes your FG down an extra 3 points. So really you're looking at 90% app. attenuation (1.051 -> 1.005), which is still high, but not that surprising for brett, especially given the temp of the PM.

Click to expand...

You just pointed out the difference between apparent and real attenuation. The OP's apparent attenuation is 96%, but would be lower taking the density of the alcohol into account. According to Beersmith the real attenuation in this case is just over 78%. But nobody really ever talks about real attenuation.

pohldogg said:

You just pointed out the difference between apparent and real attenuation. The OP's apparent attenuation is 96%, but would be lower taking the density of the alcohol into account. According to Beersmith the real attenuation in this case is just over 78%. But nobody really ever talks about real attenuation.

Click to expand...

Nope. The OP was trying to calculate his app attenuation independent of the sugar by taking out the effect the sugar had on the OG. I was pointing out that in order to find this more accurately you must also consider the effect the sugar had on the FG.

slowbie said:

It doesn't exactly work that way. Alcohol is less dense than water. Just for fun I busted out my chemistry skills from the one class I took early in college and by my math the sugar takes your FG down an extra 3 points. So really you're looking at 90% app. attenuation (1.051 -> 1.005), which is still high, but not that surprising for brett, especially given the temp of the PM.

Click to expand...

Interesting. I've been thinking about this, and it does make a difference. I had about 12% sugar (or about 1/8th of the sugars as plain table sugar). If it ferments out completely, that part of the 'mix would ferment out below 1.000, and probably get close to 0.990. With a 1.058 OG, I don't know it would have been enough sugar to convert to alcohol to get down to 0.990, so lets assume it gets to 0.992:

Assume 7 parts get to 1.004 (4x7 = 28) and 1 part gets down to 0.992. Total points left would be 28-8 over 8 parts. FG would be (28-8)/8, or about 1.0025. So the extra sugar reduced the FG by 1.5 points.

There must be some calculator out there for this. Anyone seen one. variables would be % sugar and OG and FG. Maybe I'll think about it and create one.

Calder said:

Bottled an all-brett last night. Gravity 1.002. I was expecting it to be about 1.006-1.008. Is this normal?

Click to expand...

That's lower than I've seen any of my pure brett beers go. I'm usually looking at 1.008-10. I think you might be on to something with the sugar theory though.

Calder said:

Interesting. I've been thinking about this, and it does make a difference. I had about 12% sugar (or about 1/8th of the sugars as plain table sugar). If it ferments out completely, that part of the 'mix would ferment out below 1.000, and probably get close to 0.990. With a 1.058 OG, I don't know it would have been enough sugar to convert to alcohol to get down to 0.990, so lets assume it gets to 0.992:

Assume 7 parts get to 1.004 (4x7 = 28) and 1 part gets down to 0.992. Total points left would be 28-8 over 8 parts. FG would be (28-8)/8, or about 1.0025. So the extra sugar reduced the FG by 1.5 points.

There must be some calculator out there for this. Anyone seen one. variables would be % sugar and OG and FG. Maybe I'll think about it and create one.

Click to expand...

When I made my original calcs I assumed that the alcohol formed from the glucose would be of equal volume to the water+glucose used to form it (not entirely accurate, but in the grand scheme of things it has a very minor effect on the final answer). I then found that by using one pound of sugar you had about 2.52 mol of glucose (if you used table sugar it would start at sucrose, but again, this would not make a difference as the yeast converts it to glucose). Ethanol fermentation produces 2 moles of alcohol for every mole of glucose, which means your glucose was converted into 5.04 moles of alcohol, or 232.2 grams, which comes out to 294.3 cm^3 or about 10 fluid ounces of pure ethanol. Then I used this blending calculator (the pink one at the bottom) and plugged in your blended FG (1.002), the SG of pure ethanol (0.789), and the appropriate volumes and clicked on SG #2 to calculate the FG with no sugar effects.

Hope this makes sense and feel free to check my math and point out any mistakes.