Consistently lower FG than expected

[CDS]

I'm not obsessed with gravity readings, but I'd say over the 10 batches I've brewed this year, maybe 2 came in to where I expected. The rest all had a lower than expected FG. I don't really care if it's close-ish, but the last batch of Kolsch I brewed was way off. I was looking for a lighter beer that my wife could enjoy which was supposed to be 4.7 ABV, and I ended up with a 5.8%er which is a fair difference. The screenshot are the details from what I logged in Brewfather - predicted measurements vs. actual.

I'd love to hear from folks what adjustments they would have made on brewday to bring this batch back in line.

Equipment profile: BIAB
Batch size 5.5 gallons

Recipe:
9.35 lbs Pilsen Malt
0.75 lbs Munich Light
0.30 lbs Carapils

Mash: 60 min @ 150F
10 min @ 167

Boil: 60 min

I made a yeast starter using Wyeast 2565, fermented at 64.4F with a gradual ramp up to 68F.

 

[Zteelblade]

What kind of measurement tool you are using for FG/OG readings? Did you take the c02 based on fermentation temperature into account?

 

[CDS]

What kind of measurement tool you are using for FG/OG readings? Did you take the c02 based on fermentation temperature into account?

I use a hydrometer, and no, I don't take CO2 into account, although that just means my FG is even lower than expected. The hydrometer would float higher.

 

[Zteelblade]

You are correct on that co2 effect
I assume you have also tested the hydrometer calibration is in place?

 

[TheMadKing]

1: co2 will not affect the specific gravity of a solution, and it will only throw off a hydrometer reading if bubbles adhere to the hydrometer. They read accurately in fully carbonated beer if you give them a spin and read them before bubbles alter the reading. Temperature however will throw it way off. Make sure your sample is 68F

2: the difference between your expected FG and actual is pretty small and very difficult to actually predict. There's nothing really out of the ordinary about a Kolsch finishing at 1.007. That's a perfectly reasonable FG reading so I don't think it's low enough to indicate an infection or anything. If you want a higher FG use more Cara pils (.3 lb isn't doing much for you) and mash higher. Also, you overshot your OG which compounded the issue. If you're worried about ABV I would suggest making sure to add top up water to hit your OG

I'd also recommend checking the calibration of your thermometers to verify that you didn't mash lower than you think you did

Overall your numbers look reasonable based on your grain and process, so that's where you need to adjust.

 

[CDS]

1: co2 will not affect the specific gravity of a solution, and it will only throw off a hydrometer reading if bubbles adhere to the hydrometer. They read accurately in fully carbonated beer if you give them a spin and read them before bubbles alter the reading. Temperature however will throw it way off. Make sure your sample is 68F

2: the difference between your expected FG and actual is pretty small and very difficult to actually predict. There's nothing really out of the ordinary about a Kolsch finishing at 1.007. That's a perfectly reasonable FG reading so I don't think it's low enough to indicate an infection or anything. If you want a higher FG use more Cara pils (.3 lb isn't doing much for you) and mash higher. Also, you overshot your OG which compounded the issue. If you're worried about ABV I would suggest making sure to add top up water to hit your OG

I'd also recommend checking the calibration of your thermometers to verify that you didn't mash lower than you think you did

Overall your numbers look reasonable based on your grain and process, so that's where you need to adjust.

Thanks man. I've really appreciated your insights. You've helped me figure out a few things now!
I was wondering about the attenuation numbers too...is it possible to pitch too high (i.e.: too much yeast)?

 

[TheMadKing]

Thanks man. I've really appreciated your insights. You've helped me figure out a few things now!
I was wondering about the attenuation numbers too...is it possible to pitch too high (i.e.: too much yeast)?

It's possible but difficult, and over pitching shouldnt increase attenuation much since the yeast can only eat the available food supply. So whether you pitch a little or a lot the food supply runs out when it runs out. A big pitch just improves the odds that you're going to actually hit the limit of attenuation rather than having the yeast crap out a little early

Apparent attenuation in the 80's is certainly in the higher range but it's not unreasonable give your relatively simple grist and lowish mash temp. A lot of that is yeast dependant too. I've never used that particular strain so I don't have any experience to share there