STUCK FERMENTS

Few things are guaranteed to keep a winemaker awake at night; sleep of the just you see, or maybe it's just sleep of the knackered. However, one thing is pretty much a dead cert to have us tossing fitfully and muttering about yeast and residual grams and other nonsense. That one thing is a stuck ferment. This happens when the yeast simply decide to give up the fermentation before it is finished and no amount of cajoling or threats will get it done. It's a bit like trying to get my son to tidy his room.

The reasons for the stuck ferment can be obvious, like being too hot or too cold, or sometimes there is not enough nutrient in the juice, sometimes it seems the little buggers are just being petulant. If yeast could pout and say ‘talk to the hand', that's what they'd be doing. What makes matters worse is that the yeast don't simply shut down, that would be too simple. No, they give off nasty aromas while they are busy doing nothing. Again the analogy to teenage bedrooms is pretty clear.

Getting the fermentation restarted is a real palaver. It involves endless stirring, sparging and sometimes the introduction of a ‘rescue culture'. These are strains of yeast selected for doing the second fermentation in Champagne style wines, so they are used to operating under pressure (literally). Breed up a batch of these single-celled shock troops, tip them in and hope for the best.

So far this year everything has gone really well. All my fermentations are finishing cleanly and the wines are looking great.