The “forced wort” and “forced ferment” tests are simple tests you can use to assess some aspects of your brewing. They’re new additions to my brewing procedure, and maybe not obviously useful until something goes wrong… Hopefully nothing will, but they’re easy enough that I think they’re worth experimenting with.
The “forced wort” test basically tells you whether your wort is stable and free from contamination. You take a sample from the run-in to your fermentor, before you pitch any yeast. You need a properly sterile flask for this – merely sanitised probably won’t do the job (although I haven’t tried) and could well give false positives – and you need to take the sample in as sanitary a fashion as possible. Then you simply put the flask somewhere safe and warm (on a shaker if you’ve got one – I haven’t) and check it every day for haze, bubbles, or off smells or tastes, for the next few days to see if anything grows in it. Ideally, it should still be clear and stable at least 7 days later. Don’t put it on a stir plate, as constant stirring will make the remaining proteins go cloudy (I know, I’ve done it )
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.
I’ve emphasised “sterile” a couple of times… I’m not talking about what normally passes for “sterile” amongst brewers, I mean a proper autoclave cycle. I reckon on 30 minutes in my domestic pressure cooker, according to the autoclave indicator tape. You might get away with just boiling or the usual sanitisers, but you won’t be sure, and the point of diagnostic tests is to be absolutely sure…
So, are they worth bothering with? I don’t know yet…
Dunc