Over Attenuation from Over Pitching?

[TalonsUpPuckDown]

I have a process question for the group. I’m a small batch BIAB’er (2.5g batches) and I’ve got nearly 50 batches under my belt. My process is dialed in: BH is consistently between 73%-75% regardless of style, pre-boil SG and OG are consistently within a couple thousandths of a point from what BeerSmith calculates, and every batch comes out just fine. What doesn’t jive is my FG. It is always way low from what it should be. If BeerSmith calculates 1.014, I’ll get 1.003. Same with attenuation. Regardless of yeast style (I use 4 – will get to that in a sec) my attenuation numbers are anywhere from 10%-20% higher. I don’t think it’s the hydrometer as my brew day numbers are spot on. Hmmm.

Here’s the thing. After a batch is kegged, I’m collecting the yeast slurry in two 32oz jars then storing in the fridge - I use Flagship for Pale Ales, Rogue Pacman for IPAs, London Ale for anything dark, and Wyeast 3068 for Hefs. Interestingly, I always get 64oz of slurry (it’s crazy how consistent everything is). Now, when it’s time to pitch yeast, I’m dumping an entire 32oz jar into the fermenter (remember, I’m doing 2.5g batches) so I’m clearly overpitching. Is that what’s causing the high attenuation? Is it a major crisis that I’m doing that? Couple more things. I rarely make starters anymore unless the yeast is > 6 months old. I use a hop spider then filter the wort as I’m dumping into the fermenter so the amount of residual trub in my yeast jars is minimal.

I’m not complaining or overly concerned about these numbers since my batches come out the way I like them, but I’m curious as to what’s going on. Thanks in advance.

 

[VikeMan]

In my experience, overpitching doesn't cause the kind of severe overattenuation you're apparently seeing.

First things first, have you tested your hydrometer in plain water? I know you said your "brew day numbers are spot on." But spot on to what? Beersmith can only reasonably predict what your OG should be if you have previously fed it reliable efficiency numbers, accurate boiloff data, etc.

If your hydrometer checks out and you are consistently getting extremely high attenuation, I'd start looking into the possibility of wild yeast or bacterial contamination.

 

[wsmith1625]

What temperature do you mash at and how well are you holding that temp during the mash? Also, are you adding any sugar to your recipes? Adding sugar will raise the ABV, but it also dries out and lowers the body, which means a lower FG.

 

[DevilsCups]

I feel like you'd definitely be able to tell if a beer is 1.003 dry. I just had a batch overattenuate to 1.006 and it's way drier than I'd like, but I'm crediting an accidental way lower mash temp than I planned for combined with a very fermentable grist.

 

[Jeroen79]

I would first just double check with another hydrometer or refractometer.

 

[DonT]

I use BeerSmith and it's FG numbers are always off. I've got it set up to where it's reporting SG and OG pretty close. What I do is look at what the max attenuation should be in the yeast description and change the "measured" FG to get the attenuation percentage to match the "max" attenuation figure in the yeast description. Maybe that's what you're experiencing...?

 

[TalonsUpPuckDown]

Will re-calibrate the hydro, good thought.

Mash temps are usually 151-158 depending on the style. I lose, at most 1, maaayyyybe 2 degrees but never more than that. I'm not adding sugar in any recipes.

Maybe my results are on the dry side. That's an interesting observation, thanks for that -- will check into it a bit more.

Was not aware the BS numbers are off. Will also look into your attenuation adjustment suggestion.

Great thoughts, thanks everyone.

 

[GoodTruble]

Have you used a diastaticus yeast recently?

 

[VikeMan]

Was not aware the BS numbers are off.

I think most Beersmith users would say that Beersmith's attenuation predictions tend to be pretty good. They take yeast strain, mash temp, and mash length into consideration.

One shortcoming it does have is that it doesn't change its attenuation predictions based on the makeup of the grain bill, which can get it in trouble with some recipes with large amounts of relatively unfermentable grains (e.g. caramel/crystal/dark roasted malts). But that scenario tends to make BS overestimate attenuation for those recipes, not underestimate.

 

[rmr9]

Have you used a diastaticus yeast recently?

This was my thought too especially if each batch is a harvested and direct pitched culture. You’ll easily start carrying it over from batch to batch.

 

[GoodTruble]

This was my thought too especially if each batch is a harvested and direct pitched culture. You’ll easily start carrying it over from batch to batch.

And keeps yielding the same amount of trub.

Do your beers taste as expected other than being thin/overattenuated? (...or do they all kind of taste the same.....).

 

[dmtaylor]

I'm just here to echo the same bet: diastaticus yeast, either wild or from a known source such as 3711/Belle etc.

 

[Jeroen79]

Also do you mash out to stop enzymatic activity?, otherwise there could be more sugars converted then calculated.

 

[TalonsUpPuckDown]

With respect to diastaticus yeast, I guess the correct answer is to pitch a fresh vial of Flagship and see what happens. Will do that next time around.

As to whether everything is thin or tastes the same, I can't say that's the case though it's clear from reading the forum every day that my palette is at an DIII level compared to everyone else's FBS/P5 palette (I felt a college football analogy would be appropriate). They taste great to me and everyone who tries them.

I don't mash out as my understanding is that as a BIAB'er it isn't necessary. Do I have that right?

 

[MicroMickey]

Prof. A. Fernbach said back in 1922 "Any control of the degree of attenuation should be made during mashing, and not by attempting to adjust matters subsequently."
His words have borne true in my experience; I've tried to prove him wrong.

 

[pvtpublic]

What temps are you fermenting at?

 

[TalonsUpPuckDown]

Fermenting at 68f. Hefs are higher.

 

[wsmith1625]

This experiment on attenuation has some great info . It may be from 2009, but I think the information is all relevant.

https://braukaiser.com/wiki/index.p...ity_and_efficiency_in_single_infusion_mashing

 

[GoodTruble]

Diastaticus yeast can be stubborn. They could be in the yeast you harvest or just hiding out in your equipment/lines.

Before worrying about it, just review the yeasts you've used since the attenuation issue started to see if any were diastaticus.

If they were, then yes, pitch fresh yeast, but also try to do a really thorough cleaning of your equipment and lines. It took me about 6-7 months and the same number of batches of beer to finally work a diastaticus saison yeast out my system. (But still made many good, very attenuated beers during that time =c) ).

 

[TalonsUpPuckDown]

Based on the feedback I conducted a little experiment. I split a 5g recipe into 2 2.5g brew days. To make a long story short, here's the results:

Brew 1 - Used brand new unopened packaged yeast
OG - Est 1.048, Act 1.046
FG - Est 1.013, Act 1.012
Att - Est 77.2, Act 78.1

Brew 2 - Used yeast from my yeast bank
OG - Est 1.048, Act 1.049
FG - Est 1.015, Act 1.005
Att - Est 74.7, Act 91.4

Additionally, while both beers were quite good, there was a noticeable difference between the two. The first was better by quite a bit.

So yeah, looks like we found the culprit. So yeah, now I have to build up the courage to pour my entire yeast bank down the drain. So yeah, my wife will be happy now that there's extra room in the 2nd fridge. So yeah, got that going for me.

Thanks, gang.

 

[rmr9]

I was planning to harvest from my currently fermenting helles for a märzen then doppelbock but this story has me thinking I should just pony up and buy fresh yeast

 

[dmtaylor]

I was planning to harvest from my currently fermenting helles for a märzen then doppelbock but this story has me thinking I should just pony up and buy fresh yeast

Based on ONE story? Nah! Go ahead as planned using the same yeast for each sucessive batch. I'm very confident that you'll be glad you did.

 

[rmr9]

Ha based on this story and paranoia around a dumper batch! I probably will give the harvest a go at least once.