Old Yeast..... Stuck Fermentation?

[DJM3]

Ok so I think I may be experiencing my first stuck fermentation.

I did a small batch 2.5 gallon Oatmeal Stout and all went well during the brew. Now this was always going to be a bit of an experimental batch as I was using a London ESB yeast which I had recovered from a previous Oatmeal Stout brew, I had washed the yeast and kept it in the fridge. During the boil I made sure to add plenty of yeast nutrient as the yeast was approx 1.5 months old.

I didn't do a starter as I didn't plan the brew particularly well and I found myself with a free few hours at the weekend so decided to just go for it.

When I added the yeast I was surprised at how quickly the airlock began to bubble, taking into consideration the above, after around 3 hours. This lasted for approx 24 hours and then stopped.

My OG was 1.060 and after 6 days it's only at 1.030. I was aiming for 1.018 as per Beersmith.

Also I tasted a sample which seemed to have a very thin mouth feel and a bit sour.

Could this be because of the age of the yeast? If the yeast was too old and not viable I wouldn't have expected the airlock to bubble so vigorously.

Thoughts?

Thanks in advance.

 

[archthered]

Not an expert but my first thought is what was your grain bill? If you had a lot of oatmeal and other things that add unfermentable sugars you may not be able to hit your target. Was it all grain and if so what was your mash temp? This can add more unfermentables as well.

 

[65C]

If I'm a bit unsure (I don't use a hydrometer) I give it a swirl and a couple more weeks

I've heard people say sour can come from too high an initial ferment temp - I keep my first week or so around 17C if I can (lower than what may porter yeasts recommend - but I raise it later weeks)

I have one next to my desk that only bubbled for a few days - I've given that a swirl earlier today and it's woken up again

For heavy brews like oatmeal stout (the main kind of brews I do now as they seem to work best with the water) I'll give them 4-5 weeks, sometimes 12 weeks in the primary - no idea what the final gravity comes out as but they taste like really good ones you buy so can't be far off