Ridiculous Attenuations?

[phecke]

So I've been brewing all-grain now for about 6 months and I always hit my OG almost dead on. My problem is that all of my FGs are very low, like below 1.010 low. For example I brewed an amber ale 2 weeks ago and my OG was 1.059 when I was looking to get 1.060. (The OG has been temp corrected) I was supposed to get a final gravity somewhere around 1.015. I took it today and found it to be 1.008 (also temp corrected). Thats an apparent attenuation of 86%!!! I used Wyeast 1272 (should be 72%-76%) and made a 1L starter as always. This generally happens with whatever yeast I use though, and like I said I always make a 1L starter. I also always ferment in the mid 60's.

The only thing I can figure is my mash temperatures. My glass thermo read 154˚F and I've found that one to be accurate. My digital read 150˚F but I don't trust that one near as much. Either way I don't think 86% attenuation should be possible, should it?

I'm not upset that my gravity is that low, my beer tastes fine. I'm just very curious as to how I keep getting so low, and what I can do to maybe get some more control over it.

As some more info, yes I have checked my hydrometer, it reads 1.000 in water at 60˚. Also my starters are 100g of DME/L water. I also aerate my wort with an aquarium pump and air stone.

Thought? Opinions?

 

[rocketman768]

It pretty much has to be your thermometer. Mashing at 154 F shouldn't bring you that low unless you are adding sugar to your wort. Get a thermapen or some real thermometer (NIST traceable).

 

[dcp27]

how long is your mash? longer mashes = higher attenuation

 

[Zen_Brew]

A couple of things.

1st as some others have said your mash thermometer may be off. A quick dirty check is to get a pot of water boiling on the stove and to put your thermometer in the water once it is at a rolling boil making sure not to contact the bottom of the pot. As long as you don't live in the mountains or real high elevation you should get a reading of 212 deg F.

Next where are you measuring the temperature in the mash? Try to get a real good stir of the mash and get the temp several inches below the surface. Move the thermometer around a bit to make sure you are sampling several areas of the mash.

Verify your hydrometer. Some models are designed for accuracy and calibration at 60 degrees F, and some are designed for 68 degrees F

What do your final beers taste like? Are there any funky or off flavors. I have known people to consistently get very low FG's and come to find they had some minor infection living in their fermentation conical. Wasn't enough to completely dominate the beer, but it was enough to chew through a few extra gravity points and leave a bit of underlying funk in the final beer.

 

[Frodo]

I third (or fourth?) the mash temp. I found I just did not trust any of my 3 thermometers, even though I didn't really have a good reason to doubt them. I always just wondered... I got a Thermoworks Thermapen for xmas and it's really put my mind at ease. It's so quick too, just a few seconds. I know they're expensive, but sounds like you've covered all your other bases such as hydrometer etc. Even though all the books etc really harp on sanitation sanitation sanitation, I really think temperature is just as important, particularly fermentation but also the mash temp.

 

[Atvar]

I have the same issue it seems. I just checked my 3 week old honey pale ale, and it dropped from 1.052 to 1.006. Is it normal for 8.5lb grain and 2lb honey to ferment that low?

My mash ranged from 141 to 155 depending on where/when I took the temp. reading. In the past I've been more consistantly in the 150-155 range, so this could be a factor.

This is my first time using honey, so I really don't know what to expect. When I added it, both it and the wort were 70 degrees, which might have upped the infection risk some. It fermented hard for about 3 days, then spent another 2 weeks with a gradual decrease in airlock activity. I can't smell anything noticably wrong with it, but haven't tasted yet. And now that I took the gravity reading, the airlock has been bubbling some more just to mess with my head. Argh.

 

[Lyttlewilly]

Have you tried to calibrate your eyes? Most eyes are calibrated for 1 to 2 beers before accurate FG reading can be aquired.

 

[ultravista]

"Have you tried to calibrate your eyes? Most eyes are calibrated for 1 to 2 beers before accurate FG reading can be aquired."

 

[mkling]

It's possible that it's your hydrometer. But there are other possibilities that would have the same effect. Are you doing a mashout? What temperature sparge water are you using? One of the things that's often ignored when people talk about mash time & temperature is that if you aren't doing a mashout and your sparge water isn't hot enough to get the grainbed upto ~168F, then the enzymes are still working on your wort making it more fermentable as if you were doing a much longer mash. This was a problem for me for a while when I switched from a direct fire mash tun to a converted cooler. Then I boosted my sparge water temperature to 190F so it would raise the grainbed to 168F. Once I did that, my overattenuation problem went away.

 

[sparkyaber]

I just remedied the total opposite problem (very low attenuation). Guess what- it was the mash temp. Check your thermometers, if they are accurate, start mashing a few degrees warmer, see what happens.

 

[shroomzofdoom]

how long is your mash? longer mashes = higher attenuation

I am going to second this. I was getting overattenuation as well and it turned out that even though I was nailing my target mash temps...a hour was too long to mash, in most cases I am getting full conversion at 45-50 mins. In addition, it was taking me another 20 minutes to get the wort over 170 giving the enzymes an extra 30 minutes to convert.

To fix I added a mash out step to get the mash over 170 and started this at 50 minutes. Been hitting all my FG targets since.

 

[MachineShopBrewing]

1st as some others have said your mash thermometer may be off. A quick dirty check is to get a pot of water boiling on the stove and to put your thermometer in the water once it is at a rolling boil making sure not to contact the bottom of the pot. As long as you don't live in the mountains or real high elevation you should get a reading of 212 deg F.

This is not necessarily accurate. I recently had a problem that I traced to my thermometer being off. I checked it at boiling and it read 212. I then checked it in ice water and it read 32. I had purchased a lab grade glass thermometer and checked my old one against the glass at boiling, freezing and mash range of 140-170. I found that the old one was correct at the extremes but was 4*F low at the temps in the mash range. My old one is one of those mechanical long stem, clip on thermometers. Not sure the dynamics of how this works, but just sharing my observation that checking at the extremes as is usually stated does not necessarily mean that it is reading correctly at mash temperatures.

 

[sjbeerman]

I am going to second this. I was getting overattenuation as well and it turned out that even though I was nailing my target mash temps...a hour was too long to mash, in most cases I am getting full conversion at 45-50 mins. In addition, it was taking me another 20 minutes to get the wort over 170 giving the enzymes an extra 30 minutes to convert.

To fix I added a mash out step to get the mash over 170 and started this at 50 minutes. Been hitting all my FG targets since.

This is good to know. I was wondering why I got 80% attenuation on my Belgian Wit when I mashed at 152F (65-70 min). Are you mashing in a cooler or ...? I haven't done a mash out step yet. I'd appreciate it if you could provide some details on how to do this. I mash in a 10 gal rubbermaid cooler. Thanks!

 

[Frodo]

I haven't done a mash out step yet. I'd appreciate it if you could provide some details on how to do this. I mash in a 10 gal rubbermaid cooler. Thanks!

I use a cooler too. What I do is go pretty lean on the water to grain ratio, closer to 1.25 qt/lb. Then when the mash is done, I add a water infusion to get the bed up to 170F. That infusion seems to usually be in the vicinity of 2 gal IIRC with boiling temp water. Then let it sit for 10 minutes, then start the sparge.

 

[phecke]

Thanks for all the replies! I've checked my glass thermo and it reads 32 dead on in ice water, so I have reason to trust that one, and thats the one that was reading 154.

I have noticed that even at 40 minutes my iodine tests come back with full conversion, and I've always mashed for an hour, so I could be mashing too long. I usually do my first runnings and then sparge with 190ish degree water to get the bed up to 168.

Next time I'll try mashing for 45 minutes and then doing a mash out before doing my first runnings and see if I get any difference.

 

[Frodo]

Next time I'll try mashing for 45 minutes and then doing a mash out before doing my first runnings and see if I get any difference.

I'm going to try something along the lines of that next time too. According to iodine tests I always seem to have full conversion after only 25 to 30 min, even when I mashed at 149F last time... maybe I'm doing it wrong though, and I've never checked with an iodine test after only say 10 minutes to make sure I know I'm reading it right; guess that should be on my list of things to do as well...

 

[shroomzofdoom]

This is good to know. I was wondering why I got 80% attenuation on my Belgian Wit when I mashed at 152F (65-70 min). Are you mashing in a cooler or ...? I haven't done a mash out step yet. I'd appreciate it if you could provide some details on how to do this. I mash in a 10 gal rubbermaid cooler. Thanks!

Overattenuation is also a function of dextrin formation and yeast health. Generally speaking: higher mash temp=more dextrins, less fermentable wort. Higher % of grain bill as specialty malts will also yield higher F.G. While a good starter won't break down dextrins, they will ferment a higher percentage of fermentable sugars and get your FG lower. Most overattenuation issues are easy to correct, a good yeast starter will max you out on attenuation every time so you get a feel for working with the same yeast over and over. For example, I have a CA ale yeast with a starter reliably attenuates 85% for me. I keep that value constant, and modify the mash temp, grain bill, mash duration, etc to ensure I never miss my FG

I find it helps to think of them as interdependent and sliding scales.

Yeah, I mash in a cooler too. It's not very sophisticated, but I start heating my sparge water as soon as I dough in. I then break my sparge into two equal volumes. The first sparge is boiling when I add it (usually 2 G or so), it just barely gets the temp above 170, which is perfect for me to shut down enzymatic activity.

Hope all that helps

 

[sjbeerman]

Yeah, I mash in a cooler too. It's not very sophisticated, but I start heating my sparge water as soon as I dough in. I then break my sparge into two equal volumes. The first sparge is boiling when I add it (usually 2 G or so), it just barely gets the temp above 170, which is perfect for me to shut down enzymatic activity.

Hope all that helps

I assume you drain the first runnings prior to adding your first batch sparge? What's your typical mash temp? Next time, I figured I would hit it with 190 F water to get the grain bed temp up. Also, I thought I would start draining around 45 min instead of waiting for 60 min. Is there any advantage to start heating up the first runnings while you are doing the first batch sparge other than saving some time? For some reason, I thought I heard that this was to stop the enzymatic reactions, but I figured that was related more to the grain bed temp and not the first runnings.

 

[mkling]

Is there any advantage to start heating up the first runnings while you are doing the first batch sparge other than saving some time? For some reason, I thought I heard that this was to stop the enzymatic reactions, but I figured that was related more to the grain bed temp and not the first runnings.

Absolutely! If you stop the enzymatic actions in the grainbed but not in the first runnings, you'll continue to get shorter chain sugars (more fermentable) in the first runnings over time. So heating the first runnings will also stop the enzymatic activity. Of course, it also shortens your brewday by getting your wort to a boil faster. Of course if you're doing an actual mashout so those 1st runnings have already been raised up to 170+F, then, it isn't so important.

 

[shroomzofdoom]

I assume you drain the first runnings prior to adding your first batch sparge? What's your typical mash temp? Next time, I figured I would hit it with 190 F water to get the grain bed temp up. Also, I thought I would start draining around 45 min instead of waiting for 60 min. Is there any advantage to start heating up the first runnings while you are doing the first batch sparge other than saving some time? For some reason, I thought I heard that this was to stop the enzymatic reactions, but I figured that was related more to the grain bed temp and not the first runnings.

There is advantage to heating the first runnings and doing so quickly, get them over 170 and shut down the enzymes. In my current setup, this is not possible so I had to add the mashout step.

My mash schedule is something like this:

Preheat cooler with 2G water at 172 (let sit for 20 mins, discard)
Dough in at 171-172 (immediately start heating sparge water)
Mash for around 45-50 mins (mash temps generally are 153-155)
Sparge water BOILING, I approximate runoff and add about 1/2 of my sparge volume to tun (right in top of mash/grist). Check temp of 170+ and mix, let settle for 5 minutes.
Sparge over about 20 mins.
Calculate remaining volume, add boiling water to grist. Sparge quickly--5 mins.


I brew stovetop natural gas, doing split boils. If I wait for full boil volume to be run off, combine and split into two equal SQ's...it can be 30-40 minutes before I get the temp over 170. I was having FGs of 1.003 and stuff before this. I can reliably hit my OG and FG now within 2-3 points. My efficiency is around 75% on average.

To me, the mashout was key...it's not necessary for all brewers...I just had too much enzymatic activity because I was waiting too long to get the wort over 170. Do that quickly, hit your mash temps, and know your attenuation and you should hit your FG every time.