Fixing Over Attenuation

[DerekS]

Wasn't sure if this should go into the all grain or fermentation category but figured I would start here. I know most have problems with under attenuation but I have consistently had problems with too much attenuation.

I just completed my 6th all grain batch and it has gotten better, but still not where I would like it to be. I figured with the previous batches that I was still learning my new equipment, but everything in my last brew session went perfectly and so now I have no idea where to go from here.

Mashed for an hour at 153F and only lost 1 degree. Hit my starting gravity of 1.050 and pitched the proper amount of yeast with a starter from a couple days prior containing 175 billion cells. Fermented at 66-68 degrees Fahrenheit and fermentation was pretty typical and showed airlock activity a few hours after pitching.

This recipe was supposed to ferment down to about 1.012 but finished at 1.008. I think a 4 point difference isn't too big a deal, but this is by far the closest I have gotten to my target FG. All my other brews have over attenuated by about 7 points, my last pale ale by 10 points, and a 1.074 OG beer by 11 points down to 1.007.

Previously I thought the problem may have lied within my mash temp getting below 150F during a 90 minute mash; all while falling short of my targeted OG and pitching too much yeast that was made in the starter for a bigger targeted gravity. But I have tried fixing those issues, and like I said, all my numbers were on with this last brew. Any other advice out there that can help me with the over attenuation? Because these beers are coming out dry!

 

[blizz81]

Are you confident in the calibration of your thermometer? Are you measuring temps at the end of the mash around in different spots in the mash? (Could your "one degree" be more on the sides / on the top / on the bottom of the mash?)


Outside of that, sounds like you already tried shortening mash time some. Could shorten it further as long as you're getting conversion. Could try mashing higher, using crystal malts / cara-pils / etc, but that's not really addressing the problem, I s'pose. I'm curious too as while I've minimized this problem in our setup with a new mash tun, I think we might still be coming in a bit dry compared to what, say, BeerSmith generally estimates.

 

[helibrewer]

Is this happening with multiple yeast strains or do you use the same yeast for all? What yeast strain(s)?

 

[DerekS]

Are you confident in the calibration of your thermometer? Are you measuring temps at the end of the mash around in different spots in the mash? (Could your "one degree" be more on the sides / on the top / on the bottom of the mash?)


Outside of that, sounds like you already tried shortening mash time some. Could shorten it further as long as you're getting conversion. Could try mashing higher, using crystal malts / cara-pils / etc, but that's not really addressing the problem, I s'pose. I'm curious too as while I've minimized this problem in our setup with a new mash tun, I think we might still be coming in a bit dry compared to what, say, BeerSmith generally estimates.

Yeah I have two alcohol based thermometers that coincide with each other and measure accurately. I mix really well to distribute the heat and have the two thermometers in different areas.

I have read that conversion can take as low as 30 minutes and anything after that doesn't convert a whole lot more, so I can give that a try to see what happens.

 

[DerekS]

Is this happening with multiple yeast strains or do you use the same yeast for all? What yeast strain(s)?

Yeah I have used many strains. Wyeast 2112, 1007, 1056, 1084, and 1098.

 

[drkwoods]

I would try fermenting at a lower temp. Not sure if your beer is staying at 68 or rising up as the kinetic activity produces heat. Try dropping the ferment to 65 or 66`f

 

[blizz81]

I would like to do an experiment on mash length on my system (now that I recirc and hold temp well with the RIMS) with everything else the same but maybe go 45 / 60 / 75 min to see the difference in extraction efficiency (if there is any) and attenuation, but it would mean a lot of the same beer (if I wanted a true sim I'd do it at 5gal like the rest of my batches to match), and I don't brew often enough for that to make sense.


I would think you could probably try mashing something like 4 degrees higher than what a given recipe calls for, but something again that you probably shouldn't have to change / is probably being taken into account in whatever is calculating the FG estimation.

 

[grathan]

You doing a mash out step? How long do the first runnings sit unheated while you sparge?

Why not try mashing higher, like 155-158?

The yeast strains you listed seem pretty dry to me, you could try 1968/s04/wlp002 which seems to leave more malt flavor.

How are you oxygenating? Ever tried not aerating?

 

[DerekS]

I would try fermenting at a lower temp. Not sure if your beer is staying at 68 or rising up as the kinetic activity produces heat. Try dropping the ferment to 65 or 66`f

I use a 19 gallon rope tub along with ice bottles to keep the temps stable for a week. After that first week I don't worry about the temps any longer. The house reaches 80 degrees this time of year in the afternoon. Can that increase in temp affect the primary even a week after pitching?

 

[DerekS]

You doing a mash out step? How long do the first runnings sit unheated while you sparge?

Why not try mashing higher, like 155-158?

The yeast strains you listed seem pretty dry to me, you could try 1968/s04/wlp002 which seems to leave more malt flavor.

How are you oxygenating? Ever tried not aerating?

I do not mash out. After I collect the first runnings I let my sparge sit about 10-15 minutes at 168-170F. So the first runnings all together are sitting in the kettle for maybe a half hour. Is there a difference in fermentability with mashing out and sparging?

For aeration I dump the wort from the kettle into the bucket and then shake the ale pale for about a minute and then pitch. Haven't tried any other method including not shaking.

 

[blizz81]

I do not mash out. After I collect the first runnings I let my sparge sit about 10-15 minutes at 168-170F. So the first runnings all together are sitting in the kettle for maybe a half hour. Is there a difference in fermentability with mashing out and sparging?

I think the point here is that in the time your first runnings are sitting, it could cool off enough that any beta amylase that isn't denatured by that point could continue working / could thrive. I would think if this is a viable concern that both a mash out and / or keeping heat on the first runnings after collecting would help absolve that, though I don't know that both would be necessary.


I would think this would be negligible from what I've read, but I did start keeping my first runnings on a burner on the stove while sparging on my last brew (that's still in the primary and that should be super-dry for style anyway).

 

[helibrewer]

Where in your system are you monitoring your mash temps? Where is your temp probe that is controlling the RIMs element?

 

[DerekS]

I think the point here is that in the time your first runnings are sitting, it could cool off enough that any beta amylase that isn't denatured by that point could continue working / could thrive. I would think if this is a viable concern that both a mash out and / or keeping heat on the first runnings after collecting would help absolve that, though I don't know that both would be necessary.





I would think this would be negligible from what I've read, but I did start keeping my first runnings on a burner on the stove while sparging on my last brew (that's still in the primary and that should be super-dry for style anyway).

Hmmm. That is something interesting that I had never thought about. I might start mashing out if that is the case, or at least keep the runnings on the burner and see if things change.

 

[DerekS]

Where in your system are you monitoring your mash temps? Where is your temp probe that is controlling the RIMs element?

I have a 52 quart chest converted MLT. I put one thermometer on the inside corner and the other one in the middle. Not sure what a RIMs element is.

 

[blizz81]

Hmmm. That is something interesting that I had never thought about. I might start mashing out if that is the case, or at least keep the runnings on the burner and see if things change.

Probably totally anecdotal at this point, but I just took a reading from said first batch where I kept first wort on the stove until collecting sparge and straight to the burner, and it's at 1.016. And it's a saison (with 3711 yeast, everyone describes it as such a beast) that's been in primary for 10 days.


Mashed long and low, starter, paint stirrer + drill aeration, but maybe a little cool for saison ferm (though it seemed for 3711 that wasn't a big deal). Warming it up now...

 

[rlmiller10]

I use a 19 gallon rope tub along with ice bottles to keep the temps stable for a week. After that first week I don't worry about the temps any longer. The house reaches 80 degrees this time of year in the afternoon. Can that increase in temp affect the primary even a week after pitching?

My guess is this. The temp is going high and the yeast kick back in and lower the gravity.

Try pulling a gravity sample at the point you stop maintaining temp control. If it is on target then the additional drop is after primary fermentation. There should be some after primary but not much.


Sent from my iPhone using Home Brew

 

[DerekS]

Probably totally anecdotal at this point, but I just took a reading from said first batch where I kept first wort on the stove until collecting sparge and straight to the burner, and it's at 1.016. And it's a saison (with 3711 yeast, everyone describes it as such a beast) that's been in primary for 10 days.


Mashed long and low, starter, paint stirrer + drill aeration, but maybe a little cool for saison ferm (though it seemed for 3711 that wasn't a big deal). Warming it up now...

Thanks for the update. I definitely can't wait to see how it works for me to keep it on the burner. Makes sense now that I think about the enzymes go into the BK along with the fermentables.

 

[DerekS]

My guess is this. The temp is going high and the yeast kick back in and lower the gravity.

Try pulling a gravity sample at the point you stop maintaining temp control. If it is on target then the additional drop is after primary fermentation. There should be some after primary but not much.


Sent from my iPhone using Home Brew

I have been wondering about that. Didn't even think about taking a sample before it goes up though, thank you!

 

[rlmiller10]

My guess is this. The temp is going high and the yeast kick back in and lower the gravity.

Try pulling a gravity sample at the point you stop maintaining temp control. If it is on target then the additional drop is after primary fermentation. There should be some after primary but not much.


Sent from my iPhone using Home Brew

The more I thought about this and had some more thoughts.

Fermentation is stopped by one of three things, the yeast have eaten all the simple sugars and just have nothing more go eat. Two would be the yeast have poisoned themselves with alcohol. This would only happen in a very high starting gravity situation. And three is the yeast have hit the max attenuation. This is the one I really don't understand how it works, if they have hit say 80% attenuation but there are still simple sugars in the wort to eat why would they not go farther?

So your wort obviously has enough simple sugars because the yeast are munching away down to the low OG. The amount of simple sugar is a factor of malt selection and mashing temps/steps.

The alcohol limited cause is not applicable here.

That leaves the attenuation angle, was the target FG in the recipe based on being attenuation limited? If so did the higher temp drive the attenuation farther than expected? So much to learn in this hobby.

 

[ncbrewer]

I'll throw out an unlikely possibility - wild yeast. I had an APA ferment out to 1.006. The flavor was way off, but I couldn't identify it. The guy at the LHBS tasted it and said it tasted just like a Belgian Wit. He felt that it probably got some wild yeast in it.

Edit: Several batches after that one did the same thing.

 

[catalanotte]

I struggled with the same thing for my first few batches of AG. Had a 1.055 Amber finish out at 1.006. Flavor was pretty good, but not enough body to it. Went down really easy. Here is what I have found that works for me.

I generally use about 5-15% dextrin malt (Carapils) in most beers where I want to control FG more.

I plan for an attenuation about 3% higher than the yeast is listed at for an average range. I have never had a low attenuation with a good starter, right pitch rate, and decent fermentation temperature.

I mash at a target of 154-155 and for no more than 60 minutes.

I start the mash out at about 45 minutes, to have it stabilized by then end of the hour.

I have begun mashing out by boiling 6-8 qts of the first runnings, drawn off after 45 minutes, and adding them back for the mash out. This gets the mash immediately up to 168-170.

I heat the sparge water to about 175 (it will drop almost 5 degrees when it hits your tank) to ensure the mash temp doesn't drop below 165 during the sparge.

These have both upped my efficiencies well into the 80s and helped with the FG.