Hi FG: specialist grains?

[Sandimas]

Think I know the answer but just wanted to test this: just bottled an American Porter and the FG was higher than expected, 1020, with only 62% yeast attenuation. I didn't make a note of which yeast I used but it would have been one of my generic ones which usually attenuate much higher than that.

Looking at the recipe, I used a much higher percentage of adjuct grains than I expected, roughly 30% crystals/chocolate with 70% base malt. Is that the reason for the high FG?

(no idea where the recipe came from, think it was a make-up guided by several others, think I may have over-done the specialist grains....but it tastes great!)

 

[Ghillie]

A lot of adjuncts are fermentable. Without knowing your whole grain bill and volume it’s hard to tell

Crystal malt and chocolate malt are certainly fermentable though. PPG I’m not entirely sure though, although I’d be happy to run it through BeerSmith for you.

 

[foxy]

Think I know the answer but just wanted to test this: just bottled an American Porter and the FG was higher than expected, 1020, with only 62% yeast attenuation. I didn't make a note of which yeast I used but it would have been one of my generic ones which usually attenuate much higher than that.

Looking at the recipe, I used a much higher percentage of adjuct grains than I expected, roughly 30% crystals/chocolate with 70% base malt. Is that the reason for the high FG?

(no idea where the recipe came from, think it was a make-up guided by several others, think I may have over-done the specialist grains....but it tastes great!)

I think you know the answer too, you would get very little from the chocolate, as you would have very little in there, your crystal malt though classed as unfermentable because they have mostly been converted to dextrin still has some starch in them which will convert with the base malt. Worth noting that when high levels of crystal/cara they are usually present in very high amounts and the fg is a few points higher than expected, not ridiculously high so that remains consistent as far as I can see. Just like mashing at 69 wouldn't give a beer that finishes at 1036 but might stop at 1016 rather than 1010.
A good reason for adding unfermentables at mash out.

 

[Sandimas]

A lot of adjuncts are fermentable. Without knowing your whole grain bill and volume it’s hard to tell

Recipe was
- 70% base malt
- 12% brown malt
- 12% crystal malt
- 3% chocolate malt
- 3% black malt

I constructed the recipe in Brewers Friend, OG 1052 and predicted FG 1013. It was a bit of a use-up recipe. Just curious why it finished so high, this was brew #172 and looking at my notes I've never had a yeast go as low as 62%. I know 1020 is the classic "stuck brew" figure but the FV was in a water bath with a fish tank thermometer set to 20C. The only thing I can think of is that the house did get a bit warm over the last few weeks with all the sunshine.

Edit: another thought is that I had a dodgy batch of yeast: brew #170 finished 5 points higher than I was expecting. I ran out of yeast and had to re-stock from an alternative supplier, I suppose it could have been sat on the shelf for a long time, stored too warm etc?