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Does anyone know of resources that specify the fermentability of malt extracts like muntons and coopers?

Has anyone done a forced fermentation on these extracts who has results they are willing to share?

Also, how do tools like hopville's beer calculus determine the fermentability of these extracts?

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Designing Great Beers has a table listing fermentability of a few brands of extract on p 15. I don't think it's permitted to reproduce it here, but if you search the book content in Amazon, search for "Malt extract test worts" - you'll get a link to table 3.1 which will take you right there. The range is from 45% to 65%.

I've not seen any tools that directly take fermentability for each ingredient into account. Most tools seem to estimate or use a fixed value for the fermentability of the wort, and consequently, the final gravity is also just an estimate.

For example, in Hopville, a single item recipe of 10# pale malt gives an OG of 1.056 and FG of 1.014. Plugging in a recipe hitting same OG with 7# table sugar still gives a FG of 1.014 even though in practice the yeast will ferment out the table sugar completely (provided sufficient pitching rates and nutrients are available.)

The same is also true of Beersmith - the final gravity is just an estimate (I've had this confirmed by Bradley Smith the producer of Beersmith.) The tool doesn't take into account fermentability of the wort nor the typical attenuation of the yeast, and instead uses a fixed attenuation of 75%. Note that yeast attenuation is mostly a function of the ability of the yeast to metabolize maltriose - ale yeast can at most ferment 1/3 of the maltriose, although often ferments much less due to fermentation conditions, flocculation etc., creating variability from strain to strain.

EDIT: My advice above was based on Beersmith 1. I just tried this on Beersmith 2, and for a recipe comprising only table sugar, it gives a FG under 1.000, as expected. So, my updated answer is try Beersmith 2 as a tool that takes fermentability into account, although it doesn't appear to offer the end user any control over fermentability percentages, only that the selection of ingredient type Grain/Extract/Sugar/Adjunct/Dry Extract alters the estimated FG.

See

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  • Excellent! As luck would have it I bought a copy of Designing great beers a few days before asking this question, and it arrived just as your answer did!
    – daveb
    Commented Aug 25, 2012 at 12:53
  • Keep in mind that Designing great beers is pretty dated. Its still a great book for style histories and brewing practices, but as a reference for things like extract fermentability it is sometimes quite out of date.
    – brewchez
    Commented Aug 25, 2012 at 13:32
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    Sure, that combined with the fact that fermentability of extract may vary from batch to batch - any published figures should taken with a pinch of salt. The best way to know is to do a mini ferment (not a forced ferment) to find out the typical fermentability of the extract with the chosen yeast strain. This is also covered in the book in the chapter on extracts.
    – mdma
    Commented Aug 25, 2012 at 14:57

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