Beer Forum

How do you do a fast fermentation test?
If I understand it correctly, the purpose is to find the lowest possible FG of your wort.
While running the test, do you leave the full wort just sitting there unpitched or do you run both since the full wort will take longer to ferment?

I tried searching this board, but as you can imagine, with the word "fermentation" in it, I got a bazillion hits.

I don't think its much different than making a yeast starter. Draw off a small amount of your wort, add a bunch of yeast and let it go for a couple of days or maybe only 1 day if you use a stir plate. You would do this while the rest of batch is fermenting. I guess you could use a packet of dry yeast to do this or reserve some of the yeast you used to ferment the rest of the beer.

I've seen this done at commercial breweries, but have not done this at home.

There are 2 related tests in which samples of the wort are drawn from the fermenter before pitching (wort stability test) and after pitching (forced fermentation test). The two samples are protected from the air (picture 50 mL centrifuge tubes with cotton plugs or aluminum foil over the tops) and placed in a warm environment. The forced test should ferment out in a couple of days and the gravity of the sample will give you an idea of what to expect in the main ferment though the main ferment will usually finish 0.1 - 0.2 °P higher than the force test wort.

The stabiity test sample should, theoretically, not ferment at all as it was drawn from sanitized wort. The reality is, of course, that it is indeed innoculated by wild things and will start to ferment. As long as the signs of fermentation are not visible for the first few days it indicates that the wild innoculation is unappreciable relative to the amount of yeast pitched. Conversely, if this sample starts to ferment at about the same time as the forced sample you are in trouble.

AJ, the forced ferment test can be done on a stirplate if you have one, yes?

I would also think you would want to use the same yeast you are brewing your main batch with so you will have a more accurate idea of your yeast selection's ability to attenuate your wort profile.

brewinhard wrote:I would also think you would want to use the same yeast you are brewing your main batch with so you will have a more accurate idea of your yeast selection's ability to attenuate your wort profile.

My understanding is that you can use the same yeast, or just bread yeast, since you're way over pitching the small sample, what you are really testing is how far the wort can ferment down. The flavors may be crap in the bread yeast sample, but that's not what the goal is to test for...again, from my understanding.

spiderwrangler wrote:AJ, the forced ferment test can be done on a stirplate if you have one, yes?

Don't see why not though it shouldn't be necessary. Just letting the innoculated wort sit at warmish temperature is usually enough.

mthhurley wrote:My understanding is that you can use the same yeast, or just bread yeast, since you're way over pitching the small sample, what you are really testing is how far the wort can ferment down. The flavors may be crap in the bread yeast sample, but that's not what the goal is to test for...again, from my understanding.

Information as to how far bread yeast can ferment your wort wouldn't be of much interest. What you want to know is how far the yeast you pitched can take it. That's why the sample should be drawn from the fermenter after pitching.