Gushing bottles help!

[MartinOC]

There y'go. You're spot-on. Answered your own question

A forced ferment (test-sample) result is only useful for the particular (main-batch) fermentation you're using it on.

 

[Pogierob]

Is the addition of more yeast required? Or is the test meant to be on the viability of the original yeast?

 

[MartinOC]

The test shows you the limit of attenuation you can expect from the wort/yeast combination in your main fermentation, not the viability of the yeast. It's usually done near the beginning of a ferment (ie. after aeration & pitching).

The result will usually be slightly lower SG than your main batch (because you're "forcing" the sample to it's absolute limit), but if your main ferment seems to have stalled, you can work-out where it is in relation to the 100% attenuation from the test & maybe up the temperature a bit, rouse etc.

 

[stux]

Yeah Martin,
I was just thinking that a saison with Belle Saison should have an apparent attenuation of 80-90%+ while say US-05 should have 70-80%. So if your saison seems to stall and all you have on hand is us-05 and the forced ferment drops in SG then clearly the saison isn't finished as the belle should have even more left in it than the us05?
Having time to think about it, I've realised that even if I'm not thinking about this all wrong, it is a silly thing to do. If the SG doesn't drop I've wasted a us05 and proven nothing. I'll make sure if I do it in the future to use the same yeast.

Which is why you can use bakers yeast, which comes in a large container for little money.

Better than nothing, and better than wasting a good yeast.

 

[MartinOC]

Which is why you can use bakers yeast, which comes in a large container for little money.

Sorry, Stux. I think you're missing the point of doing a forced ferment test here... it shows the limit of a particular wort/yeast combination, not simply of the wort itself. Unless you're fermenting your main batch with baker's yeast, adding it won't show you anything worth knowing.

 

[manticle]

Is the addition of more yeast required? Or is the test meant to be on the viability of the original yeast?

You can do either. Shake the warm sample to see if you can push the yeast any further (has it stalled?) or if it's finished. To test the maximum attenuation of the wort itself and see if fresh yeast will get you more, add new stuff. Different methods give different information.