Slow or Stuck Fermentation on Experimental Pale Ale?

[jeffceo24]

Hi Everyone,

I made an experimental pale ale with an extract kit that was about 6+ months old. I used fresh US 05 yeast. The original kit OG should be 1.046 and 4.7% alcohol when done.

I added 2 x 14oz packages of guava paste to make an experimental guava pale ale. I cut them in cubes and added them 15-20 minutes before the end of the boil and dissolved them in the wort. The ingredients didn't list any preservatives.

My OG was 1.056 on 2/24. I haven't seen any airlock activity for a while so I checked the gravity last night and it was 1.022. (with refractometer) This is only a 60% attenuation and 4.46% abv per the brewers friend calculator. This is after 24+ days fermenting. There does appear to be more trub than usual.

It has been fermenting at relatively low temps. 60-62 deg for most of the time and about a week at 64 deg. Any ideas? Thanks!

 

[ncbrewer]

I wouldn't expect the 6 month old extract to cause low attenuation. I've never fermented US 05 that cool, but it seems like it's been fermenting long enough now anyway. Whether you pitched dry or rehydrated shouldn't make that difference. Before going into other causes, let me ask: Have you had other fermentations get stuck like this, or is this unusual for you?

 

[HomeBrewMasterRace]

The issue is you're using a refractometer to get final gravity; you have to use a hydrometer because alcohol doesn't deflect light in the same way the water in the wort does.

I'm also presuming you let it ferment for 2 weeks.

 

[jeffceo24]

let me ask: Have you had other fermentations get stuck like this, or is this unusual for you?

First time for me, although our downstairs is cooler than usual.

you have to use a hydrometer because alcohol doesn't deflect light in the same way the water in the wort does.

I'm also presuming you let it ferment for 2 weeks.

Thanks HomeBrewMasterRace, you must be on to something. I knew about the alcohol in the refractometer but I thought I had the right calculator to convert it. I just found another calculator here: https://www.brewersfriend.com/refractometer-calculator/
I'll look at my refractometer and see what my readings would have been in Brix and try converting from there. If not, I'll just rack to my keg and get a big enough sample to use the hydrometer. It has been over 3 weeks now. Thanks!

 

[HomeBrewMasterRace]

That's the good calculator.

How much sugar was in the guava paste? It could just be mostly non-fermentable material. I had a pumpkin beer finish at 1.24 because I added alot of pumpkin paste to the boil

 

[jeffceo24]

Good point. Could be a lot of non-fermentable material. My bazooka tube was clogging as I drained the wort into the fermenter. I calculate 18 ounces of sugar per the guava package