Low ABV Grumpy Troll

[HeavensBrew]

As my 3rd attempt at all grain brewing using BIAB, I decided to try the Grumpy Troll Belgian IPA. The recipe was from the book 'Big Book of Clone Recipes'. It should be a whopping 9.2% ABV, but I ended up with 5.8%.

I had adjusted quantities for BIAB and and a 10l rather than a 19L batch. Where I had deviated was the choice of yeast. I went from a White labs liquid yeast to a Mangrove Jacks dried yeast. I had thought that maybe I needed 2 sachets for that high an ABV, but it was only a 10L batch (the equivalent of 2 sachets for that volume).

The OG was 1.0775 when it should have been 1.093. That will be the fault of my technique (I've improved and the next beer has a higher OG than prescribed).
The final FG should have been 1.024, but was still 1.035. That gives me 5.8% ABV vs the 9.2% that it should be. I had even maintained the required temperatures for each phase of fermentation.

It's bottled now and 5.8% is fine if it tastes good. I was just wondering if this was just the fault of the OG or if there is something else I need to learn?

Hope it's good and I can understand the issue. I want a high alcohol to weight beer for taking on the occasional hike.

 

[Linalmeemow]

I'd be concerned that at 1035 it hasn't finished fermenting properly...

 

[strange-steve]

Agree with the above, that's only about 53% attenuation which is low for any yeast, especially a Belgian strain. Which yeast did you use?

 

[HeavensBrew]

I used MANGROVE JACK'S BELGIAN ALE M41
Total fermentation time was 16 days. 20C for 7 days and the remainder at 27C. No more bubbles and it remained at 1.035 for a few days. The recipe expected 14 days.

Beer is bottled and inside sealed plastic containers as my usual precaution. Perhaps I should test the first bottle after 7 days?

 

[Linalmeemow]

I used MANGROVE JACK'S BELGIAN ALE M41
Total fermentation time was 16 days. 20C for 7 days and the remainder at 27C. No more bubbles and it remained at 1.035 for a few days. The recipe expected 14 days.

Beer is bottled and inside sealed plastic containers as my usual precaution. Perhaps I should test the first bottle after 7 days?

In my experience Belgian yeasts can take a LONG time to fully ferment out, though I've never used M41.

I don't mean to cause alarm but you do need to be careful with your bottles here. Did you use glass or plastic? How much sugar did you prime with? Were the bottles designed for higher pressures (have you used Duvel bottles, for example)?

 

[HeavensBrew]

Standard glass beer bottles purchased for homebrew that have been used many times before.
Recipe called for 150g for 19L. I used 80g for 10L.

Surely the fermentation is over if the FG has not budged for a few days and it's longer than the recipe? I know that a 27C ferment would make things move faster.

I could always open a bottle outside every 5 days and put them in the fridge if things are getting feisty.

 

[strange-steve]

Surely the fermentation is over if the FG has not budged for a few days and it's longer than the recipe?

Ideally yes, but it's not uncommon for some yeasts to knock off a bit early (although most Belgian strains are admittedly pretty reliable), and the problem comes when they are kickstarted by something like racking or priming. I would be very cautious with those bottles.

 

[HeavensBrew]

This leaves me with some final questions:
1) What should I have done differently and how should I have known? Should I start to routinely leave the wort an extra week once the fermentation has stopped for 3 days?
2) What to do with the bottles?
I am thinking of opening one after 3 days and I will know I am safe if it is pretty much uncarbonated. However, what should I do if it is carbonated? Straight to the fridge and start consuming early or start pouring down the sink?
3) How do you calculate '53% attenuation' and what is the rule of thumb on that particular percentage?

PS. I have 15L of a clone of Squatters Pub Brewery: Full Suspension Pale Ale in an FV.The target OG was 1.043, but I got 1.046. The yeast was pitched on Thursday morning and held at 20C. Seems like the fermentation has stopped on that as well (no more bubbles), but this morning I will be dry hopping some Columbus for at least 3 days.

 

[strange-steve]

1) What should I have done differently and how should I have known? Should I start to routinely leave the wort an extra week once the fermentation has stopped for 3 days?

Don't assume that fermentation is complete after "x" amount of time, check the attenuation level to see if it seems about right. If you're not sure give it more time. Two weeks is usually enough time for fermentation to finish but some brews just inexplicably take longer. If it sticks, then bumping the temperature up a little and giving it a gentle stir can sometimes get it going again.

2) What to do with the bottles?
I am thinking of opening one after 3 days and I will know I am safe if it is pretty much uncarbonated. However, what should I do if it is carbonated? Straight to the fridge and start consuming early or start pouring down the sink?

I would carefully and with appropriate caution moniter carbonation levels by opening one occasionally, and if they start to become overcarbonated then keep them as cool as possible. Bottle bombs can be dangerous, so keep the bottles in a container or under wraps somehow.

3) How do you calculate '53% attenuation' and what is the rule of thumb on that particular percentage?

To work out attenuation:
(OG - FG) / OG * 100
Just use the gravity points, so for your example it's :
(78 - 35) / 78 * 100 = 55%

Yeast manufacturers will give you a typical attenuation range for each strain. A low attenuation would be maybe around 65 - 70%, medium around mid 70s, high around 80%+.

 

[Hanglow]

What did you use to measure FG? If it was a refractometer then that reads very high when alcohol is present

 

[HeavensBrew]

Thanks for the answers.

Just dry hopped the Full Suspension Pale Ale in an FV. I checked the gravity and that seems stuck at 1.020.
Using your calc, that's 56.5% attenuation as opposed to the 72% in the recipe. Now off to swirl it about a bit!

 

[strange-steve]

It seems a little odd that you've had two brews in a row with mid 50s attenuation. @Hanglow makes a good point, you're not measuring FG with a refractometer are you?

 

[HeavensBrew]

Yes, I am using a refractometer for both FG and OG. Wort at 20C for both.

This must mean I have something else to learn! What's the issue with refractometers?

 

[Hanglow]

Yeah! Your wort is more attenuated than you think

have a read through some of the links here and try out the calculator. There may be better calculators out there too
https://www.brewersfriend.com/refractometer-calculator/

 

[strange-steve]

Yes, I am using a refractometer for both FG and OG. Wort at 20C for both.

This must mean I have something else to learn! What's the issue with refractometers?

That's a good call by Hanglow and very good news for you. Refractometers are not accurate when there is alcohol in the sample, due to the different refractive index of ethanol compared to water. There is a correction factor that can be applied, but even better would be to get a hydrometer for FG readings.

The good news is that according to the calculator linked by Hanglow your Belgian IPA has an FG of around 1.011 meaning 8.7% abv and 86% attenuation, and better yet you won't have bottle bombs.

 

[Linalmeemow]

That's a good call by Hanglow and very good news for you. Refractometers are not accurate when there is alcohol in the sample, due to the different refractive index of ethanol compared to water. There is a correction factor that can be applied, but even better would be to get a hydrometer for FG readings.

The good news is that according to the calculator linked by Hanglow your Belgian IPA has an FG of around 1.011 meaning 8.7% abv and 86% attenuation, and better yet you won't have bottle bombs.

@Hanglow to the rescue! That's a good spot, and SS is right, it looks like you're safe!!!

 

[HeavensBrew]

Thanks for working through this problem with me. I'd never have known otherwise. So a refractomer is only useful for: 1) OG and 2) testing that the fermentation has stopped. But it's time to get out the hydrometer for the true FG.

Just used the hydrometer on the current FV and it is 1.012 instead of 1.020 I'd read with the refractometer. That's a 74% attenuation and 4.46% ABV

 

[Horners]

A story as old as time. All power to the forum.

 

[Zephyr259]

I haven't used a hydrometer in almost 2 years now, I spent 18 months using both to work out the correction factor of my refractometer which reads 1.5% higher than my hydrometer. Then I've imported the formulae that accounts for alcohol into a spreadsheet and use that to do all the sums. Over that time the FGs were generally within 1.002 of each other which is the accuracy I often felt I had in reading the hydrometer.

As you say refractometers are also brilliant for checking that FG is stable with a tiny sample. What ever works for each of us.