Hello and welcome to our weekly video, this week I am drinking beer from the East Sussex based brewery Burning Sky. This is a West Coast Pale called Out of Vogue, I would expect this beer to be up there with the best as Burning Sky simply cant do anything wrong, I have loved every beer I have tried from them, if you have not given them a go then it’s a must. You can buy direct from their website and also various bottle shops country wide.
We have many questions from brewers via email but one of the ones that “stuck” out this week was about fermentation issues and especially what appears to be a stalled ferment. Let’s have a look at why this may happen, how to prevent and how to solve the issue.
A stuck or stalled ferment is one that takes off as expected, then slows down somewhat before stopping at a gravity above where the brewer is expecting the final gravity to be. One really important factor here is that your visual signs of fermentation such as airlock activity and krausen must be backed up by measurement. It could well be that fermentation is complete, just a lot quicker than the brewer has expected
A stuck ferment shouldn’t happen in if you have used an all malt grist, pitched enough healthy yeast and aerated your wort correctly. However, as we all know sometimes things go awry.
So firstly lets look at the malt bill, if you are using 100% malt then there should be enough nutrients in the wort for healthy fermentation. However, it maybe that you are using a quantity of sugar or a higher percentage of maize or rice. This is where adding nutrient will be necessary; there are several available such as Servomyces or indeed our own brand nutrient. Just add it in the last 10 minutes of the boil.
Take a good look at the yeast that you are using and follow the instructions for that particular yeast. Even yeast from the same brand have different instructions according to strain, some yeast are higher attenuating, some need higher temperatures throughout the whole ferment, some just for the final couple of points and this is true for the new Verdant IPA yeast. It maybe that your ferment has stalled because the wort has dropped in temperature, it has moved out of the temperature range of your chosen yeast. Again, this needs to be backed up, do measure the temperature.
Again, looking at the instructions on the yeast, making sure that you are pitching enough healthy yeast is imperative, if using dry yeast this is normally quite easy as most yeasts sachets are designed for 40 pint batches. Do be aware that the some of the Lallemand dry yeast including Nottingham and their Londan ale have varying pitching rates of between 0.5 and 2g per litre of wort. We add the pitching rate for these yeasts in the product description, so you do need to take note.
If using wet yeast then this needs looking at closer. We stock many different brands and they all differ slightly in their approach. Whereas dry yeast has a long shelf life, the wet yeast is less so. This is why we add the best before dates of each strain listed on the website, customers know exactly what they are purchasing. When we send the yeasts via courier we always add an ice gel block, this gets packaged with the yeast in a bubble bag. So the yeast should arrive to the customer in great condition. If this is the case then go ahead and pitch as per instructions
However, it maybe you missed the courier, or indeed they missed you. Maybe the yeast didn’t get put in the fridge right away, there are going to be scenarios where you can guarantee the yeast is in pitch able condition. In this case making a yeast starter is essential, you need to guarantee that the yeast you’re pitching is on it’s A game or you will have problems down line, don’t pitch and hope. I have added a blog post on how to make a yeast starter, it is not difficult, takes little equipment and a good skill to have as a brewer.
So, you have taken on board all the above but you are still in the “stuck Ferment” situation, what do you do. There are a few options; you may have been advised to rouse the yeast by giving it a stir, I would not go down this path as you risk oxygenating your wort and this is an irreversible, it will be a dumped batch. You could try adding a fresh pack of yeast, this may not work if there is not enough oxygen present in the wort plus there could be enough alcohol present to kill the yeast. My favoured method is to add a batch of healthy yeast at high krausen, this means that the yeast is fully active, it wants to ferment. So, you need to make a fresh yeast starter, with the same or similar yeast strain and pitch when you see the most vigorous signs of fermentation, this is called Krausening. Use the calculator available on our website to work out a starter size, or how much malt extract to use, for a 40 pint batch to kick start a ferment I would be looking at a 1 litre starter, an easy way to do this is to have a can of Propper Starter on hand.
So to summarise, following good brewing practise will minimise your risk of fermentation issues, but, arm yourself with the knowledge of your options if it goes awry.
Have a great weekend, see you next week.