Final gravity

[Bombers hoppy ending]

Hi ladies and gents. Quick question regarding yeast and FG.
What is it that determines FG and causes the yeast to stop. Is it alcohol tolerance or residual sugar.
Ie. I understand that yeasts have tolerance to alcohol, so if a yeast has an alcohol tolerance of 7% ABV and an expected FG of 1014 due to an OG of 1072, what happens if you lower the OG to say 1058. Will the yeast still expect to stop at around 1014 due to the level of remaining sugar or will it carry on dropping to below the 1014.
Reason for asking is that I started a new munstons west coast kit that was supposed to be a 7% IPA. I wanted to lower the ABV to nearer 6%. So added some extra water. Lowering the OG from 1072 to 1058.
The kit uses US05 yeast.
After 9 days the SG was checked 1018 so dry hopped.
Checked SG on day 13 1008.
Checked again today day 15 1007.
This is currently giving ABV 6.7%. Not what was expected but ok.
Just wondered why such a big difference from the kit expected FG 1014 and my current 1007.
Finally would you consider a 0.001 change over 2 days as good enough to say it’s finished and ready to bottle, or would you leave another few days.

 

[NotSure]

My understanding is that the best way to see how a yeast strain is going to perform in a given wort is to do a Fast Fermentation Test using the same wort. I've never done one, but if I'm unfamiliar with the strain, I wait until I'm reasonable sure there's no activity before bottling. From what you're describing, I wouldn't bottle yet.
Regarding your question as to when yeast stop.... it's both attenuation limit and alcohol tolerance. However, I've found attenuation limit to be quite relative and alcohol tolerance to sometimes be conservative. With US-05 in particular, I've gotten 14.5% ABV in a mead. Considering the yeast's upper limit is 11% ABV, take the numbers with a grain of salt.

 

[Bombers hoppy ending]

Thanks for the rapid response.
I’m in no rush as such to bottle. I’m away this weekend so will leave it till next week. All my previous beers have had 3 weeks in the FV and have turned out great, so not concerned. First time I’ve had one over shoot the expected FG by so much and wondered if it was a result to brewing it long.
Tastes lovely from the trial jar.

 

[NotSure]

Thanks for the rapid response.
I’m in no rush as such to bottle. I’m away this weekend so will leave it till next week. All my previous beers have had 3 weeks in the FV and have turned out great, so not concerned. First time I’ve had one over shoot the expected FG by so much and wondered if it was a result to brewing it long.
Tastes lovely from the trial jar.

The kit makers might have just changed the ingredients a bit and it ended-up being a bit more fermentable. No worries.

 

[Bombers hoppy ending]

I believe from reading on here that they did make changes it after it’s initial trial period and this must be one of the first kits as it was only released a few weeks ago. Huge amount of fermentables as it has 2 cans and 1kg of brewing sugar.
I shall leave it to do it’s own thing and clean itself up, and bottle next week.
Thanks again.

 

[cushyno]

Yeast manufacturers sometimes just state high/medium/low attenuation, which is next to useless. Others give a range, such as 75-79% apparent attenuation. It's the percentage figure that helps here. If the kit suggested 1.072 OG and 1.014 FG, that's an approximate apparent attenuation of:

100 * ((72 - 14) / 72 ) = 80.6%

Which is likely in reality to be a range 78-83%
So, with OG if 1.058 and mid range attenuation of 80.5%, your expected FG would be:
58 * ((100 - 80.5)/100) = 11.3 or 1.011, but could be between 1.010 and 1.013.

That's the theory based on the kit's stated figures. Yet, if the kit manufacturer has subbed in US-05 for some other yeast they usually use in the kit, you will never know what to expect!

Doing a quick Google on US-05 turns up plenty of posts about people getting 86% -ish attenuation from that yeast, which would be in the same ballpark you're seeing - 1.007-1.008.

It pays to do your homework on expected attenuation as I recently found out with a WY1469 that hugely over-attenuated on the manufacturers figures, but it's apparently not uncommon for that yeast. You live and learn.

 

[Bombers hoppy ending]

That’s incredibly interesting. Love learning and thanks for the input. The yeast was marked as US05 so I imagine, in these latest line of kits that would be the case.
Be interesting to see when I bottle it next week, if it has now stabilised at 1007.
Thanks again for the info.

 

[Northern_Brewer]

Hi ladies and gents. Quick question regarding yeast and FG.
What is it that determines FG and causes the yeast to stop. Is it alcohol tolerance or residual sugar.

It's pretty rare for alcohol tolerance to be a limiting factor - beer yeast typically survive up to around 10-12% ABV, although some puke out as low as 8%, some go up to 14+%. Usually fermentation stops because the yeast run out of stuff they can ferment.

Think of fermentation like climbing a mountain - let's say that 1000m represents 100% attenuation, fermenting 100% of the carbohydrates in the wort/juice. Mount Wine has a nice paved path all the way to the summit, even people in wheelchairs/baby buggies/mobility scooters can go all the way to the top - the carbohydrates in grape juice are almost all simple sugars which any yeast can metabolise.

Mount Beer is not like that. The paved path only goes up to 700m, and wine yeasts and the likes of Windsor/S-33 can't go any higher. The path up to 800m is kinda rough and you need good boots to walk up it. The likes of US-05 and Nottingham have the boots - or enzymes that can digest maltotriose - that can get this far. Beyond 800m are sheer cliffs which need climbing gear to climb - only diastatic yeast have the specialist enzymes needed to break down the most complex carbohydrates. And then the last 50 metres is a greased metal pole which nothing can climb short of taking a chainsaw to it!

 

[Bombers hoppy ending]

What an awesome analogy. Thanks for the trouble taken to write that. Certainly makes things easier to understand.

 

[Festival Man]

Hi ladies and gents. Quick question regarding yeast and FG.
What is it that determines FG and causes the yeast to stop. Is it alcohol tolerance or residual sugar.
Ie. I understand that yeasts have tolerance to alcohol, so if a yeast has an alcohol tolerance of 7% ABV and an expected FG of 1014 due to an OG of 1072, what happens if you lower the OG to say 1058. Will the yeast still expect to stop at around 1014 due to the level of remaining sugar or will it carry on dropping to below the 1014.
Reason for asking is that I started a new munstons west coast kit that was supposed to be a 7% IPA. I wanted to lower the ABV to nearer 6%. So added some extra water. Lowering the OG from 1072 to 1058.
The kit uses US05 yeast.
After 9 days the SG was checked 1018 so dry hopped.
Checked SG on day 13 1008.
Checked again today day 15 1007.
This is currently giving ABV 6.7%. Not what was expected but ok.
Just wondered why such a big difference from the kit expected FG 1014 and my current 1007.
Finally would you consider a 0.001 change over 2 days as good enough to say it’s finished and ready to bottle, or would you leave another few days.

The things that determine the FG of your brew are 1 yes the amount fermentable sugars that the kit contains and also the amount of unfermentables present in it., and 2 the volume of water that you are using.You have increased the volume of water by circa a fifth, your alcohol content on your gravity drop has been reduced by one fifth you say. It is interesting to hear that by adding a fifth of the original volume on top, you have managed to halve your potential FG.

 

[Bombers hoppy ending]

I’ll shall be taking another reading Monday when I get home. Interesting to see if it’s settled. Hope it hasn’t carried on going, showing a possibility of infection.

 

[Bombers hoppy ending]

Home from the weekend and checked the gravity. Between 1.006-1.007 today so dropped possibly 0.001 in 5 days. I think I’m calling that finished and bottle tomorrow. That puts the ABV @ 6.8%.
Trial jar tasted ok.