Raspberry IPA, high FG

[Snrub]

Hi All

I brewed a Raspberry IPA three weeks ago, recipe indicated target OG of 1.059 and FG of 1.016.

Pitched 2 x packs of rehydrated American Ale yeast so plenty for a batch of 23 litres. The same yeast finished a Black IPA brewed the same day in just a handful of days.

Ther fruit addition was 2.1 kg raspberries at the end of the boil. I got 1.054 for my OG (for what a hydro reading is worth at that stage).

After 2 weeks in the FV @ 19 degrees I took a hydro sample but found it so full of (raspberry?) gunk I couldn't get a sensible reading, so dropped the temperature to 2 degrees for a week to cold crash the sediment out. Which it's done nicely, but now I find my hydro reading to be 1.020 - a fair bit higher than I expected.

The reading has been steady for 4 days which indicates it's done what it's going to do, but 62% attenuation is pretty low for that volume of yeast. I'm considering that the yeast I used was a brand from my local homebrew store (Bulldog) which I haven't used before and maybe less reliable than more famous brands, but then the same brand and volume of yeast sorted the Black IPA as expected.

Would the fruit addition have added more unfermentable sugars that would explain a higher FG?

Advice much appreciated.

Cheers,
Mr Snrub

 

[Sadfield]

I think the likely affect of adding the raspberries is that it added plenty of simple, easily fermented sugars to the wort. The problem with this can be, yeast consume sugars in order of complexity, simplest first, and can flocculate out, stop fermenting before they've consumed the more complex dextrins. Did your recipe have any crystal/Cara malts in it?

Have a look at this thread to hopefully get back on track.

https://www.thehomebrewforum.co.uk/...s-for-dealing-with-stuck-fermentations.74910/

 

[Snrub]

4% Crystal & 4% Carapils. Also 8% lactose if that's relevant.

Thanks for the advice - was thinking of raising the temperature and rousing anyway.

 

[stz]

Hydrometers are calibrated to typically 20c and will read high in cold samples. lactose is unfermentable and will remain. 54 @ 80% attenuation gives 45 so a PG of 9 plus 8% lactose approx 13-14 with a final expected with temperature comp of 19

 

[Snrub]

Hi @stz - I really appreciate the explanation but fear I haven't followed correctly - can you just confiorm for me please?

Hydros read high in cold samples - OK - I actually left the sample to warm to room temp - now reading 1.018.

Lactose is unfermentable so I need to factor in that satisfactory attenuation won't make it as low as predicted.

Have you calculated my expected FG @ 1.013-1.014 @ 19 degrees, or an FG of 1.019?

Sorry for being a thicko!

 

[Cwrw666]

If your expected FG is 1.016 and you've got 1.018 - isn't that near enough?
Certainly if I was looking for an FG of 1.010 with a brew and got 1.012 I wouldn't think I had a problem.

 

[Sadfield]

How many g of lactose into how many litres of wort?

Roughly 1.2g/L of lactose will give you a gravity of 0.43 gravity points. If you multiply this value by how many g/L you've used, then subtract it from your measured OG and FG, you'll get a better idea of your attenuation. Assuming you added the lactose into the boil.

 

[Snrub]

If your expected FG is 1.016 and you've got 1.018 - isn't that near enough?
Certainly if I was looking for an FG of 1.010 with a brew and got 1.012 I wouldn't think I had a problem.

Yeah TBH if I'd measured it at 1.018 in the first place I probably wouldn't have posted the question!

 

[Snrub]

How many g of lactose into how many litres of wort?

Roughly 1.2g/L of lactose will give you a gravity of 0.43 gravity points. If you multiply this value by how many g/L you've used, then subtract it from your measured OG and FG, you'll get a better idea of your attenuation. Assuming you added the lactose into the boil.

500g into a 28L boil which yielded 23 litres of wort. So using your calculation - somewhere between 1.97 (using 23 l) and 2.4 (using 28 l) gravity points = 1.052->1.016 = 68%. Still a bit lower than I'd expect for that yeast, but shifts it from the "somats gone wrong here" category to the "sod it lets get it in the bottle."

Cheers everyone for the advice!

 

[stz]

Your recipe was supposed to be 59 to 16. This is apparent attenuation of 73%. Your recipe started at 54. Your final gravity would with the same attenuation would be 14.5. You mention 8% lactose. When I use percentages I mean percentage of total extract so 4.32 points. This won't ferment. Expect a final with temperature compensation of 18.83. If you look at the attached chart you'll see correction @ 2C is 2.2 at 1.020. If you read 1.020 at 0C then you can lose a couple of points. 1.01771 would be my predicted provisional gravity. This is all theoretical and subject to extrapolations.

 

[Sadfield]

It's much easier to add lactose at bottle/kegging. It can then be done to taste and doesn't add any confusion when determining attenuation.

Edit: Pre-dissolved in a small volume of hot water.

 

[stz]

Straight in the underback on collection for me. Impossible to mix in cold beer.