anyone do forced fermentation tests?

[Waterlogged]

I am doing an IPA on Monday. Yeah flex day!  So I decided to use a wyeast british ale for one of the 3 carboys.  Made a starter last night and while I was reading up on starters (only my 3rd one), I came across some discussions on forced fermentation test for determining the termanal gravity of your wort.  Basically, you save a small amount of wort from your batch, say 1 l, and then you over pitch it with yeast on a stir plate and let it ferment out for 24-48 hours.  You then measure the final gravity and this will be the gravity to aim for to determine when your beer is finished.  Sounds simple enough so I decided to give it a try.  Has anyone else doe this and of so, any comments on its usefulness?

Reid

[Two Wheeler]

I just trust beer smith, and if I'm worried about it I take samples two days in a row

[Bellick]

Excellent and simple test to run, especially if you don't have any data on what the terminal gravity should be.  Lets you know A) when to package and B)if you have any contamination.

[Waterlogged]

I somewhat agree with two wheeler about beersmith but that assumes you get the mash temp and sparge temp correct and everything goes as planned. However, my brew days seldom go as planned.

[jamie_savoie]

I'm not sure if I understand correctly Reid.  When you say you overpitch the saved litre with yeast, do you still pitch yeast to the main batch or you wait till the test litre is done then pitch that yeast into the main batch?  Is the goal of this to know exactly when it's safe to process the beer?

I usually wait at least 3 weeks before processing any of my beers so I'm never worried if it's done fermenting or not.  I'm too lazy to check the gravity 3 days in a row lol.  I'd rather be patient and let the yeast finish cleaning up after itself.  Even if it's done fermenting doesn't mean the yeast is finish working

Beersmith is predictable if all the variables are spot on but it's rarely the case for me too. To predict my FG I go with my past logs and experience with said yeast.  Best example is brew a 1.050 saison with 3711, mash at 158, BS will estimate a FG of 1.012 when in reallity it'll finish < 1.005 or lower guaranteed

[Waterlogged]

The "forced ferment" test tells you what the maximum attenuation you could get for that wort and yeast combination is. You take a sample (large enough for at least one gravity reading) from the fermentor after you've aerated and pitched the yeast, and incubate it it warm conditions and with frequent shaking (preferably on a stir plate or shaker) to force it to attenuate fully. We're not really worried about how it tastes, so we can use high temperatures and stirring, but again you need a sterile flask and to take the sample aseptically, as any contamination could change the results. Once you know the maximum possible attenuation, you are better placed to make decisions how fermentation is progressing and to diagnose any problems with over- or under-attenuation. It should finish fermenting well before the main batch, so you can use the information to decide things like when to raise the temperature for a diacetyl rest, or when to rack for conditioning.