Dr Brew gives some stellar advice to help us with our homebrewing.

Q: Help, I’ve added the yeast but my wort is not fermenting! 

BE PATIENT

So my first question would be how long have you waited? If it’s only been 24 hours or so then don’t worry just yet. It can sometimes take up to 96 hours until you see some foam on the surface of your wort and bubbles in your airlock. If it’s been that long then check the points below and re-pitch ASAP using a suitably rehydrated dry yeast, giving the wort a really good stir with a sanitised spoon to aerate it.

CHECK FOR LEAKS

Secondly, are you sure it’s not fermenting? A lack of air bubbles in your airlock might not necessarily mean that the yeast isn’t working! You might have a poor seal between the lid and your fermentation bucket. So check that it’s on securely. Don’t worry if it’s been exposed to oxygen at this stage, it’s only a problem once primary fermentation is complete. Also, you do have enough clear liquid in your airlock to check for bubbles, right?

SUFFICIENT AERATION

Talking of oxygen, yeast does need O2 to work so give your FV a gentle swirl to get the yeast back into suspension and get some more oxygen into the wort.

DIRECT PITCH OR REHYDRATE DRY YEAST?

Next question: did you just sprinkle the dry yeast into the wort? Ideally - to ensure its viability - you should rehydrate dry yeast before adding it to your wort to wake it up. While it can be OK to pitch dry yeast directly into the wort it can make some of the yeast cells inactive, meaning that the remaining ones have to work harder. Like us humans, yeast gets stressed when overworked and can create undesirable flavours and aromas during the fermentation process. This is because the sugars in the wort block the yeast from absorbing enough water, which is needed to trigger the yeast’s metabolic activity. Rehydrating dried yeast only takes 20 or so minutes. Be sure to check the rehydration temp recommendation for your yeast.

TAKING CARE OF YOUR YEAST 

Is your yeast out of date, or has it been incorrectly packaged and/or stored? Some things are OK if they are a little out of date, but don’t risk it with your yeast. If you used a smack-pack of fresh yeast, did it swell up properly before using? If not, the yeast might not have been viable.  

PITCHING TEMPERATURE

What was the temperature of your wort when you pitched the yeast? If it was too warm it will really reduce the viability of your yeast. It might even kill it. If it was too cold the lag time might be longer, or it might not work at all. In which case, you’ll need to bring your wort back to temperature and re-pitch more yeast. So make sure you check the recommended ferm temp and pitch rate on your yeast packet before pitching. If it’s not on there, look it up online. Generally, ale yeasts are pitched at around 18-22°C and lager yeasts 9-15°C. Kveik is a different beast.

PITCH RATE

Another point is making sure you have pitched the right amount of yeast. The packet should indicate how much. Too little might well increase your lag time so when it does finally get going the yeast has to work much harder, giving out those esters and other off-flavours you want to avoid. Or it might stall your fermentation too quickly. Don’t worry, it’s quite unlikely you will over pitch.

FRIDGE FRESH LIQUID YEAST

Lager yeasts, for example, might be OK direct from the fridge but if you’re making an ale, did you allow the fresh yeast to come up to pitching temperature? Again check your packet for guidelines.

FERM TEMPERATURE

Another thing to think of is whether you have the right fermentation temperature for the yeast you’re using. Check the temp of your wort now. You might have to carefully relocate your FV to a cooler/warmer place. Or use a heat belt if it’s too cold. Also, be sure your temp is consistent! 

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