Like all homebrewers, you want to make great beer. There are a lot of great beer recipes that detail the ingredients and general steps but don’t always say if you should stir your wort after pitching yeast.
You should not stir your wort after pitching yeast as it can create yeast clumps or splash the yeast onto the sides of the fermenter. Simply pitch dry yeast, liquid yeast, or a yeast starter into the fermenter and wait about 30 minutes for signs of visible fermentation activity.
Keep reading to see more on whether you should stir or not as well as the importance of oxygen to yeast.
Should you stir the wort after pitching yeast?
Stirring seems the obvious thing to do after adding yeast to your wort. You want to mix everything together in the hopes that it will give your yeast the best chance of fermenting properly.
However, you shouldn’t stir the yeast into your wort. Stirring can cause yeast cells to clump together and stick to the side of your fermenter outside of your wort.
While this isn’t a huge issue, it isn’t worth it. Not to mention, each time you interact with your beer after boiling the wort there’s a chance to infect it. Stirring in the yeast after pitching only benefits wild bacteria and yeasts.
In most cases, there is no reason to stir your brew during fermentation. You can read more about stirring during fermentation here.
Dry yeast is the most tempting to stir after pitching. The yeast seems to settle on the top, not mixing in. This is perfectly normal.
The dry yeast will take some time to rehydrate. After doing so, it will mix and settle into the wort liquid and begin the fermentation process. You can, however, rehydrate it before pitching.
Rehydration is a simple step you can take while your wort cools. This step isn’t necessary but can increase the viability of the yeast.
Liquid yeast, or rehydrated dry yeast, is really simple to pitch. Since it does not need to rehydrate it will mix in and begin to work.
When pitching with liquid yeast there is no particular need to stir.
By its nature, liquid yeast will naturally settle into the wort and begin doing its work quickly without the need to rehydrate.
A yeast starter is similar to liquid yeast. The difference is that the starter includes a basic wort and the yeast cells have already started reproducing.
Just like liquid yeast, there is no need to stir after pitching. In fact, it is better not to so the yeast can move on to the anaerobic stage of fermentation.
Yeast starters can be easy to make if you have a stir plate. If you don’t have one, don’t worry. We have a guide for you!
What does it mean to aerate the wort?
Homebrewers like to throw around terms that can be confusing to those just starting the hobby. I know that I’m guilty of it too, but one term that is used describes an important step: aerating the wort.
Simply put, aerating is the process of reintroducing oxygen to the wort. This can be as low-tech as shaking the wort in the primary fermenter to as high-tech as using specialized equipment.
This step is necessary because boiling the wort removes all the oxygen.
Aerating should be done before fermentation begins. For the yeast to survive there needs to be oxygen present when it is pitched.
There are a few different methods used to aerate such as:
- Shaking the wort in the fermenter
- Pouring the wort between containers
- Using an aquarium pump
- Using an O2 diffuser
Any of these methods – if done right – will improve your beer. Oxygen allows the yeast to better reproduce, improves attenuation, and reduces the chances for off-flavors.
Why does yeast need more oxygen at the beginning of fermentation?
Every living thing goes through various stages in its life cycle. Oxygen is just as important to yeast as it is to us. There are, of course, some differences.
In its first stage of fermentation, yeast uses oxygen to synthesize unsaturated fatty acids (UFA) and ergosterol. These compounds are responsible for proper yeast growth after the oxygen has been used up.
This process helps the yeast build up its membrane structure. Yeast cells’ membranes help them reproduce asexually in a manner called budding. The stronger the membrane the more they can reproduce without being stressed.
Without oxygen, yeast does not have the chance to synthesize the UFA and ergosterol. Additionally, there is no chance for aerobic cellular respiration. This can cause off-flavors, slow yeast reproduction, slow fermentation, and reduce yeast viability.
Do you aerate before or after pitching yeast?
It is important to note that oxygen can be harmful to your beer once the yeast has used up all that was initially available. At this point, the yeast will switch to anaerobic respiration which is the step in which it makes ethanol and carbon dioxide.
Oxidized beer tends to taste similar to wet cardboard, paper, or leather. This is why it is important to only aerate before you pitch yeast. These off-flavors may not come up if you don’t, but the risk isn’t worth it.
It is still possible to aerate afterward, but it is not recommended.
Aerating immediately after pitching will have the lowest chance of these side effects because the yeast will not have started the fermentation process.
However, certain methods of aeration take longer than others and fermentation may start as you aerate. Once fermentation has started it is too late to aerate.
Should you stir the yeast starter?
Yeast starters are essentially small batches of beer so there are many similarities in how you should treat it. What is different is the purpose.
You should stir or otherwise agitate the starter while it is being made. Once it has been pitched into your wort there is no need to stir.
By stirring, swirling, or using a stir plate on a yeast starter before it is pitched, you keep the yeast in the aerobic respiration stage. This keeps the yeast reproducing instead of fermenting.
If you stir after pitching it would only slow the fermentation as well as the earlier mentioned side effects.
See the web story version of this article here.