As brewers, we may try to take all the credit for our tasty beer when friends and family sample it, but we have a deep dark secret. In fact, we hardly did any of the heavy liftings during the brewing process, it was the yeast we used!
So, it’s no wonder that brewers are so concerned over the wellbeing of their yeast, if only in a rather selfish way. There is nothing worse than when yeast stops playing ball and leaves us on the sidelines feeling confused and powerless.
So, how can you tell if your beer yeast is dead or merely inactive?
To see if the yeast in beer is dead you need to monitor its specific gravity over several days. If the specific gravity reduces, this means sugars are being consumed by living yeast. Stirring the beer can resuspend yeast & reanimate it. If no change occurs, then your yeast is either dormant or dead.
There are really two different approaches to determining if your yeast is alive and kicking or not, and I will cover both of them in the following article. Basically, there are things you can do to ensure that you don’t ever use yeast which is already expired and other methods to check if the yeast you’ve already used is dead.
Things to check before you pitch your wort
- If using a brewing kit, make sure you check the expiry date on the yeast package. As a general rule of thumb, just replace that yeast with a similar variety you have recently purchased.
- Make sure that the yeast you are using has been allowed to reach the same ambient temperature as your wort or at least room temperature. This avoids shocking the yeast to death.
- Conversely, make sure that you aren’t pitching your yeast at temperatures that are too low. The cold will send your yeast to sleep.
- Make sure that your equipment, in particular, your fermenter is thoroughly rinsed and no trace of sanitizer remains as this could kill off your yeast.
- If using dry yeast make sure you rehydrate it (even when not instructed) in water (95-105°F/ 35-41°C) for less than 30 minutes. Dumping dry yeast into the warm wort directly could kill up to 50% of it immediately.
- Make sure that you have aerated your yeast by either stirring it, shaking it gently or by using some sort of carbonation device. Yeast needed oxygen to live, so make sure that there is enough in your wort.
- Ensure that you are using enough yeast for the job (although even one cell could ferment 5-gallons of beer given enough time). 10-15 grams of yeast per 5-gallon yield is about right.
- Take a specific gravity reading before you pitch your wort and then another one about 30 minutes to an hour after. This is going to be your baseline for later use.
Things to check after you pitch
- Take a specific gravity reading daily until you see a clear indication of fermentation such as bubbles of the creation of krausen (see my article for more details on this). Any reduction in SG will give you an indication that fermentable sugars in the beer are being gobbled up by the active yeast.
- Keep a record of the temperature of your brewing room AND your fermenting vessel. Remember that fermenting beer can rise in temperature by a couple of degrees, so make sure that you can keep the temperature in the right range for your yeast strain.
Important things to remember:
Beer yeast suffers from the goldilocks phenomenon when it comes to temperature, too hot and it’s going to shuffle off this mortal coil, too cold and it’s goodnight for a while. So, it’s really important to keep these temperatures in check.
If you are brewing in colder climates, you need to keep that fermenter warm with blankets, sleeping bags, heating pads or anything else you can think of. If you are brewing in a hot country, as I am now, then you may need some fridge space which you can regulate to keep the right temperature during fermentation.
Below are some examples of common yeast strains and the big difference in the ideal fermentation range for each:
Min. Temp. (°F/°C)
Max. Temp. (°F/°C)
California Ale Yeast
1028 London Ale
WLP029 German Ale
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Although we want the yeast very much alive and active when in our fermenting beer when we aren’t using it the opposite is true. Ideally, you want to force the yeast into inanimation as much as possible so that it will last longer, at least until the next brew day.
When storing yeast, you have to consider the difference between dry and liquid yeast as they can be stored in different ways and have different pitfalls to be aware of.
A dry yeast packet can certainly be left on a shelf as long as it’s a dry and cool place. You don’t have to refrigerate these packets, but it will certainly extend their lifespan. Even if you don’t put these packets in a refrigerator (34°F/1°C) you can expect them to last more than twelve months with only a 1-2% loss of yeast cells per month. Many brewing kits opt for dry yeast because of this, and as long as you rehydrate the yeast before pitching it’s a good option.
Liquid yeast can be a little more temperamental and is more susceptible to changes in temperature or being exposed to direct sunlight. Without exception, you should refrigerate your liquid yeast at around 34°F/1°C. Liquid yeast, even when at this temperature, will lose a whopping 20% of the yeast cells inside per month, so you shouldn’t be using liquid yeast stored more than 6 months.
Ideally, you should buy the liquid yeast and use it within days or weeks of purchase. With this type of yeast, a good yeast starter is the best way to get the most out of the yeast cells and get your batch off to a great start!
Using a small wort batch to check for dead yeast
Say for some reason you can’t check the specific gravity of your beer, your dog ate your hydrometer or something, how else can you check for dead yeast? Well, introducing your beer’s yeast into a tester sample is one method I can think of.
This calls for some additional unhopped wort, about 1 quart of water (946 ml) and around 5 oz of DME. So, this will only really work if you have access to another batch or can squeeze out a little more wort from spent grains you have knocking around from that brew day.
I idea here is to introduce your beer sample to the unpitched and cooled tester wort sample and see if any magic happens. By this I mean, if the beer doesn’t show signs of fermentation within a day or so, then it’s likely that the yeast in your main batch is indeed past its prime.
However, I would always say keeping a hydrometer or refractometer handy is far easier in determining the activity of your yeast than carrying out this science experiment. If you want to know more about using a hydrometer, check out my article on this topic right here.
How long does it take for yeast to activate in beer?
On average you need to wait for about twelve to thirty-six hours for the yeast to really get into the early stages of fermentation. Of course, this depends on many things from the strain of yeast, to temperature, to oxygen levels in the beer, to the number of nutrients in the beer as well as the number of yeast cells themselves.
So, if you pitch your beer in the morning, you should see something happening by that evening or the next day on average. If it’s been more than 3 days, it may be time to start troubleshooting.
How do I know when my beer is done fermenting?
Again, the best way to know if your beer is fermenting is to take a scientific approach and whip out your hydrometer to take a specific gravity reading. This is just monitoring the density of your beer which tells you how much fermentable sugar is present in the liquid. As yeast digests this sugar the density of your beer will change.
However, for a more visual approach, you should look at the surface of the beer and watch for bubbling, belching and the formation of a brownish foam called krausen on top of your beer. If you’ve set up a blow off tube, then you can also see bubbles flowing out of it into your container full of sanitizer. For more information on why and how to set this up, check out my article on the topic here.
However, don’t purely rely on the visual cues for fermentation. The formation of krausen and bubbles can be very active in the initial stages of fermentation, but then quickly die away to almost nothing. This doesn’t necessarily mean that your fermentation is done. So always monitor the changes in the beer’s specific gravity.
If you do think that your fermentation has stopped too early, check out my article on how to fix this issue.
Dangers of repitching? Can I add more yeast to my beer?
If you really have no way of monitoring the specific gravity of your beer or if you feel that there aren’t enough viable yeast cells in the mix, should you just add some more? What is the worst-case scenario if you do?
Contrary to popular notion, it’s not how much yeast you have in your beer which makes in carbonate, it’s how much nutrients you have for the yeast to feed on. More food leads to more carbon dioxide which leads to the carbonation of your beer. So, in this case you won’t ruin your beer just by adding additional yeast.
Directly pitching yeast
As always, make sure that you don’t directly add your yeast into your beer. This swift introduction to a new environment can actually kill off a large proportion of the yeast cells and make the remaining cells ‘stressed’ so that they underperform. Makes sure that when using liquid yeast you prepare a yeast starter and that you rehydrate dry yeast before it ever touches your beer (or wort).
Does fermentation kill yeast?
In very general terms, yes it does. However, inactive yeast isn’t always a sign of death by alcohol poisoning. This being said, if all goes well the alcohol content in beer will force yeast cells to full out of suspension, flocculate together and fall to the bottom of your fermenting vessel as trub.
So, in a way, you could say that every brew day is like a suicide mission for beer yeast. Nevertheless, not all the yeast will fall victim to the ethanol in the beer and it is possible to harvest those yeast cells for future use.
Does more yeast mean faster fermentation?
Counterintuitively, no it won’t. Having double the amount of yeast cells in your beer won’t actually speed up the fermentation period, it could in fact have some rather nasty results.
Having additional yeast, when the majority of the yeast cells are active, can lead to off-flavors through excessive production of esters. (for more details on off-flavors see my article here).
Yeast cell growth is a very important factor in the fermentation process and having too many for the nutrients available seems to have an adverse effect on beer production.
The only circumstances in which you should add additional yeast is if you are sure that your fermentation has stopped due to dormant or dead yeast cells being present. This can best be checked, as I’ve mentioned before, by checking the specific gravity changes of your beer over several days.
So, as you have read, the very best way to ensure that your yeast isn’t dead in the fermenting vessel before its time is to ensure that the brewing temperature is within the correct range and it has been stored correctly before use. After you have pitched the yeast, the only accurate way to tell if the yeast is still with you or not is to take a specific gravity reading with a hydrometer or refractometer and watch for any changes.