We haven’t brewed for a while. Since moving to all-grain brewing last year, we’ve had a couple of successes – a tasty mild and a blackberry wheatbeer, for example, as well as some drinkable if unremarkable bitters. However, we’ve suffered stuck fermentations in the last couple of brews, and it’s been rather depressing. All that effort, and you end up with sugary water.
(Note – a stuck fermentation is where it starts off fine, but stops fermenting before it reaches the expected final gravity. Final gravity should be around 25-30% of the original gravity. So our last brew had O.G of 1053, but only got down to 1025, i.e. 45%)
This has happened twice (and in fact, our third-from-last brew only got down to 35%), and we can’t understand why this has started happening – we’re not doing anything different with the yeast or aeration, which seem to be the usual culprits for stuck fermentation.
We consulted all our books, and searched the internet, and came up with the following theories (and counter-arguments).