Stout hasn't reached final gravity

[foxy]

Yet the website I linked says it does equate to fermentability.

And it was you who said this a couple of years ago:

Yes and I just said it again a few moments ago. The fermentable sugar to be got from highly kilned malts is going to add some fermentability but very little. They will be adding more none fermentable sugar than fermentable as you found out.

 

[Stu's Brews]

There seems to be a lot of confusion in this thread about what gravity points, PPG and fermentability mean, to try and provide some clarity...

Specific gravity points are simply a measure of the total amount of sugar dissolved in a liquid. It does not provide any indication on how fermentable those sugars may be. Original gravity is controlled by how much sugar is extracted from your grain (i.e. quantity of grain, grain type, mash efficiency) and how much liquid evaporates during the boil. PPG describes how many gravity points you can expect to extract from one pound of grain in one gallon of wort.

Fermentability is a term used to describe how easy it is for yeast to ferment the dissolved sugars and subsequently produce alcohol. A high level of fermentability will result in a lower final gravity (less sugar is left in solution, more alcohol is produced). A low level of fermentability will have the opposite effect. Fermentability is controlled by mash temperatures, mash pH and the type of grains used. Higher temperatures will give lower fermentability as more long-chain sugars will be present in the wort. A slightly higher mash pH (e.g. 5.4 v 5.2) can increase fermentability. The use of crystal, roasted or dextrin malts can all result in lower fermentability.

You can have any combination of high or low original gravity and high or low fermentability. These are two of the key tools a brewer can use to adjust the overall balance of a beer.

Disclaimer: other factors may also affect the original gravity and fermentability but I've tried to keep it brief by focusing on the main ones.

 

[Sadfield]

If OG has been overshot to the point where 3L dilution is required, then the degree of fermentability of 500g of roasted malt isn't going to have much bearing on the outcome. There clearly wasn't an issue with the mash.

At least we've clarified that unfermentable grain is partly fermentable.

 

[peebee]

You can have any combination of high or low original gravity and high or low fermentability. These are two of the key tools a brewer can use to adjust the overall balance of a beer.

Nice summary. Sound conclusion. Just one slip I could see: "... two of the key tools ...". There's only one!

The other, for "high and low fermentability" doesn't exist for homebrewers (that's a challenge! I want someone to prove me wrong with where I can get one from). It would be really handy to have more idea of the resultant sugars in the wort: How much Maltose, how much Malt-triose, how much even longer chained stuff (plus miscellaneous stuff like glucose, sucrose, etc.). But we have no such tool and have to make "educated guesses", although with experience you can make quite good "educated guesses". And then you have to pair that with what you know about the yeast you are using: What it can or can't do with "malt-triose", or is it (gawd forbid) a var. diastaticus strain? Again, with experience of the yeast you can make quite good "guesses".

But that other tool would be dead handy!

 

[Stu's Brews]

Nice summary. Sound conclusion. Just one slip I could see: "... two of the key tools ...". There's only one!

The other, for "high and low fermentability" doesn't exist for homebrewers (that's a challenge! I want someone to prove me wrong with where I can get one from). It would be really handy to have more idea of the resultant sugars in the wort: How much Maltose, how much Malt-triose, how much even longer chained stuff (plus miscellaneous stuff like glucose, sucrose, etc.). But we have no such tool and have to make "educated guesses", although with experience you can make quite good "educated guesses". And then you have to pair that with what you know about the yeast you are using: What it can or can't do with "malt-triose", or is it (gawd forbid) a var. diastaticus strain? Again, with experience of the yeast you can make quite good "guesses".

But that other tool would be dead handy!

Maybe just a poorly written sentence on my behalf... I meant that those are two things that a brewer can control:

1. You can influence whether you have a high or low gravity through increasing/decreasing the amount of malt used.
2. You can influence whether you have high or low fermentability through increasing/decreasing the mash temperature.

I'd be similarly interested in a 'tool' that can give you insight into the wort composition - would be fascinating to see how it varies for each brew.