Chronic under attenuation

[roblanderson]

I started brewing about 1.5 years ago with my two brothers - between the 3 of us we've probably done 20 batches, half extract & half all grain. I am consistently not getting the attenuation I'm expecting.

Looking back at the first few batches I completely get it - I had wild temp swings during primary fermentation and was under-pitching yeast by just dumping in a single smack pack (5 gallon batch). Then when moving to all grain, which we do BIAB style, we mashed in the higher range (154-156) for the first few batches.

For the last 6 or 7 brews I've tried several things to improve attenuation and the beer in general:

• I make an appropriate starter using MrMalty as a guide and have also tried using rehydrated dry yeast to increase yeast cell count
• Added yeast nutrient
• Bought a chest freezer & temp controller to tightly control fermentation temps
• Bought an O2 wand/stone and directly infuse with O2 instead of shaking the carboy
• Lowered mash temps - I've been mashing around 150 lately
• Water adjustments using Bru'n Water to get the right PH and mineral balance
• Choose a yeast strain that typically gives higher attenuation

All of these things I would say have improved the product, but I'd like to know what else I can try.

For a recent example, I brewed a 1.050 Oatmeal Stout about a month ago. BIAB mash at 150 for 60 minutes. I used 1 packet of S04 yeast and after 3 weeks in primary the FG had stopped at 1.020. No lactose by the way. I was hoping for a FG around 1.015. Not a huge difference and the beer isn't bad, I just wish it was better.

 

[RM-MN]

When your initial fast part of the fermentation is over, do you move the fermenter to a warmer location to sit for the rest of the time? I've been doing that and I'm dealing with over attenuation instead and have been trying a higher mash temp and shorter mash time to try to adjust for that.

 

[LLBeanJ]

Is your thermometer accurate? I had a similar problem until I got a Thermopen. It confirmed that my $20 CDN digital thermometer was off by 4 degrees at mash temps. Problem solved.

 

[bhanson]

You've accounted for many of the general recommendations regarding better attenuation already. There are still a couple of things that might lead to a higher final gravity reading than expected -

Have you tried using a different water source entirely, rather than doctoring the same one with adjustments / nutrients / O2? It's feasible that there's something already in the water that shuts down fermentation once the yeast get closer to being stressed by the environment. Unlikely, but feasible. Do a batch starting with spring or distilled water as a test.

Are you measuring the final gravity with a hydrometer or refractometer? A refractometer requires an adjustment to the reading in the presence of alcohol. A 1.020 reading could be dramatically lower. Ignore my ramblings if you are using a hydrometer.

Temperature is the most likely variable that you haven't mentioned. Raising the temperature during the latter parts of fermentation will help the yeast finish. Raising S-04 to the 68-70 range after fermentation is mostly complete will have very little impact on esters or other flavors at that point.

 

[Pie_Man]

Seems like you are doing all the right things. One thing to do is calibrate your thermometer. It's possible you are mashing higher than you think. Also, how long are you mashing?

For your next batch, I would brew something with a very simple grain bill, like a Pilsner or Pale Ale. I don't know your gb for the oatmeal stout, but stouts often use higher percentages of lower attenuating grains which may be your issue on that batch.

 

[Weezy]

How confident are you in your mash temps being what you say they are? do you recirc? Are you mixing/stirring often to avoid hot or cold spots? how are you maintaining and controlling temps?

Is your thermometer accurate and precise?

try oxygenating for 5 minutes with the wand turned on at a trickle, not a blast for 30 sec.

After the krausen falls, bump the temp up 3 degrees.

 

[MKBoitnott]

The above me have suggested that you make sure your measurement are correct. Very important I would say. Always measure twice before you jump to other conclusions.

Now, once you have made sure that is right... s04. I have been reading lately (and probably posting too much) about varying opinions of how much s04 is in a packet. Mr. Malty would say that there are 220 billion yeast cells in there. But other people have found different results. Especially with s04.

I refer you to http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

They list differing research on dry yeast.

Others will probably tell you that "I pitch one pack of s04 into a beer all the time, and it works for me." I wouldnt question their expertise, but the main suggestion I would propose is to simply avoid dry yeast if possible. Thats coming from direct email conversations with Mr. Malty himself.

 

[roblanderson]

Thanks for all the responses and ideas!

To answer the questions:

• I don't very the temp in my fermentation chamber - I've just left it constant.
• I am not confident in my thermometers. We have used 2 digitals and 1 one analog. They all measure 32 in ice water and 212 in boiling water (+/- .5), but at mash temps there is about a 6 degree spread. Perhaps I should spend the money on a Thermopen. Lately we've just been averaging the 3 temps for our recorded mash temp.
• We haven't done a batch starting with a different water source - I'll add that to our to-do list
• All measurements with a hydrometer
• We've done all of our mashes at 60 minutes. Sounds like a 90 minute mash might improve wort fermentability, so that is also on our to-do list
• We actually recently bought the equipment to re-circulate during the mash and hope to have that setup for our next brew. Up to now we've been stirring manually 2 or 3 times during the mash. We cover the mash with a thick sleeping bag and typically only lose 1-2 degrees during the 60 minutes.

Our next brew will be a Kolsch. We did this one as an extract 8 months ago. and it turned out very good except for the slightly high FG. OG was 1.055 and the FG was 1.016. This time it will be all-grain - we'll try extending the mash time to 90 minutes, lowering the mash temp, bumping the fermentation temp towards the end, and possibly using RO water.

 

[Weezy]

Those last 3 I would try for certain.

 

[MKBoitnott]

Definitely make sure to confirm your pitch rate on the Kolsch. Very important for that style.

 

[mjohnson]

If you don't want to spend the cash on a thermapen, look at getting a glass lab thermometer. They can be fragile for everyday use, but you'll be able to tell which digital thermometer is closest at actual mash temps. They're usually less than $10.

 

[IL1kebeer]

Recipe plays a role also.

Try something simple like a 1.055 beer made with 2row, a half pound of crystal40, about 40 IBUs, and an appropriate pitch of WLP001. With an average mash temp you should finish between 1.010 and 1.013 depending on your system and fermentation. If you finish high with this recipe then your problem has to be process or equipment related (such as hydrometer or thermometer calibration). If you hit your numbers on this one then you should go back and check your old recipes for flaws that could cause high FGs.

 

[roblanderson]

We've done two 10-gallon batches recently - a Kolsch & a Robust Porter, each split into two 6-gallon carboys for fermentation with different yeasts.

The Kolsch was 95% pils and 5% vienna. Target mash temp was 149 and we mashed for 90 minutes. OG was 1.051 and we used Wyeast 2565 & WL029. We held the temp at 66 degrees for the first 5-6 days and then ramped it up to 70 once fermentation had visibly slowed. Both finished at about 1.013 for an AA% of 74%, within the guidelines for each strain.

The Robust Porter had a more complex grain bill:
33% US 2-row
33% Golden Promise
14% Munich
7% Crystal 60
7% Chocolate
3% Black Patent
3% Flaked Oats

We mashed for 60 minutes at 151 degrees. OG was 1.059 and we used Wyeast 1275 Thames Valley & Wyeast 1098 British Ale - both higher attenuating yeasts. Fermented at 67 degrees for 5 days and then ramped up to 70 to finish off.

The 1275 Thames Valley fermented down to 1.019 and the 1098 British Ale was one point lower at 1.018. 67% & 68% attenuation, both well below the stated levels in the low/mid 70s.

In both cases we did a BIAB style mashout - where once the 60 or 90 minutes of mashing was complete, we fired the burner with the grain sack still in the pot and pulled it out once the temp hit 168.

 

[Weezy]

How do they *taste*? Those FGs aren't bad, and I wouldn't call that under attenuating given the beers described. Do they taste too sweet for you? If so, I think you're at the point where you just may want to mash at a lower temp. Your process sounds just fine to me!

There's not much or any value to a mash out with BIAB. That's typically for long, fly sparge where the grain may be subjected to high pH or high temps, resulting in tannin extraction from the grain. With BIAB especially, where you yank the grain and get to boiling pretty quick, there's no real fear of pH or temp interaction with the grain and there's no long time between mash and boil to worry about prolonged enzymatic action in the wort.

 

[roblanderson]

Taste? Does that really matter if the numbers aren't right?

These 2 recent batches haven't been tasted yet in their final form. The kolsch is still lagering and the porter is still carbonating. The flat & warm samples do taste very good though.

While we've enjoyed all of our batches, they do seem to all be a bit on the "heavy" or full-bodied side. This has been most noticeable on the couple batches we did over the winter there were supposed to be nice and crisp - a cream ale & a saison.

 

[GotPushrods]

I am not confident in my thermometers. We have used 2 digitals and 1 one analog. They all measure 32 in ice water and 212 in boiling water (+/- .5), but at mash temps there is about a 6 degree spread. Perhaps I should spend the money on a Thermopen. Lately we've just been averaging the 3 temps for our recorded mash temp.

Unfortunately this is quite common, which is why I recommend calibrating each dial thermometer to the temperature closest to where you'll use it. i.e. 170 HLT, 150 MLT, 60 BK

Are the digital ones fairly close together and the dial the outlier? Having 1 you trust implicitly is a great idea for any brewer.

 

[roblanderson]

At mash temps, the two digitals are 4 degrees apart. The analog is harder to read accurately and seems to vary quite a bit.

What we've been doing recently is just averaging the two digitals. So if our target is 151, then we look for the low one to read 149 and the high to read 153.

 

[stpug]

Taste? Does that really matter if the numbers aren't right?

Actually, you've got that backwards:
Numbers? Do they really matter if the taste is right?

Obviously, this would be within reason but the answer is, no, the numbers don't matter if the taste is right. Your numbers are well within reason and there can be numerous reasons why you're finishing a little higher than expected. Your process leads to the low-end of published yeast attenuation values; mine leads towards the higher end. I would like to find the middle range for several styles. The easiest control over than is mash temp which will simply help with body and ABV, and that's about it. Sweetness of beer comes more from ingredient choice, bitterness, and yeast choice than it does FG and mash temperature - assuming complete fermentation.

Since you have three thermometers that can't agree on mash temp - you say 6 degree spread at mash temp - then you need to pick the one that is slightly on the high side. So, if you're aiming for 153F and you have one reading 155F and one reading 151F then start only using the one the reads 155F. It becomes your regular brewing thermometer and provides the consistency from batch to batch. Next batch, you aim for mid-low temp (152F) using that thermometer and a trusted attenuating strain like US05, WLP001, WY1056 and see where it lands after fermentation. After you figure out how the thermometer works for you then you simply adjust, mentally, during your next brewday for using that thermometer. If your beer came out spot on then use it's reading at face value; if your beer came out a little higher FG than expected then consider it's reading to be 2F high; if your beer came out a little lower FG than expected then consider it's reading to be 2F low. Brew again, and see where it comes out. Your thermometer doesn't need to be precise to be useful, it simply needs to be consistent and accurate. For instance, if you know a thermometer is consistently reading 3F lower than actual then you know how to mentally adjust it's reading

One other point to hit is your fermentation schedule. Some yeast strains are more forgiving than others when it comes to cooling down. Some, like US05, doesn't care a whole lot about some cooling down and will continue to keep working. Some, like 1028, put themselves to rest once the temperature swings even 1 degree lower than during active fermentation. When you're using non-forgiving yeast strains (most british, some belgian, some others) you need to take a different approach to fermentation schedule if you want high-end attenuation for that strain. My current schedule is: pitch warmer than I'd think (66F), keep it there until fermentation begins (i.e. don't let it slip lower), let fermentation bring the temps up to 68-72F depending on strain, keep there for 2 days, after 48 hours of active fermentation, bring the fermenter into 70s room temperature and leave it for a week before checking gravity. Basically, I'm moving my fermenter from fermentation chamber to 70s room temperature while active fermentation is just finishing up but before the fermenter temperature starts to slip. I've had pretty good success with some low attenuators this way. Another benefit of this kind of schedule is that it open up your fermentation chamber quickly for new beers.

Edit:
Just to add another point, multiple thermometers lead to questionable readings. If you only ever had and used one thermometer you would know how it works for your system. Pick your most trusted and roll with it. I have a thermoworks non-thermapen because I wasn't sure which of my other three thermometers to trust; the glass analog, the dial, or the cheap $2 foreign import. I decided to buy a thermoworks brand. As it turns out, the $2 import reads the exact same as the thermoworks it's just a bit slower

 

[LLBeanJ]

^ There's some solid advice right there.

 

[Weezy]

Its hard to fight temp variations across a kettle. You can always start recirculating.

If your targeting 151 now and it may seems bit sweet to you, target 149 next time. Your process is working so I wouldnt fret over slight temp variations...try moving your target first, as a simple first step.