Brew Tips #11: Yeast Pitching Rates and Preparation
The last couple batches I put in primary I was playing with different means of pitching my dry yeast. Starter vs. rehydrating vs. dry pitching as well as tweaking with pitching more or less yeast. Some recipes in BeerSmith were suggesting I use 2 packs of dry yeast. So, I also wanted to know if that was actually a good practice, especially since the calculation really just rounds up even if the ideal amount is really just 1.1 packs.
Before I dive in, if you're making a high gravity beer, pretty much everyone is in agreement, do everything you can to improve odds as these are most at risk of a stalled fermentation. And in these cases a starter may actually make sense. Or even better, pitch onto a yeast cake from a lower gravity beer. But, as a general rule for more regular strength beers, I think what I'm going to say makes sense.
Preparing yeast beyond dry pitching takes time. Which means I definitely wanted to understand the benefits, if any. Rehydrating yeast wasn't affecting me much. I simply take the yeast out when I start brewing and pitch it into a cup of room temperature water while the wort is cooling, which takes 30+ minutes in my bath tub anyway. But, nonetheless, even that seemed pointless. After all, if it isn't a high gravity wort, you're not really doing anything that won't happen when you pitch dry anyway.
I didn't keep the link, but in my research I stumbled across an article where an individual did some test batches with different pitching rates and another article where yeast preparation was discussed. And the results were actually quite interesting.
As far as prep goes, making a starter or rehydrating actually run the greatest risk of hurting your yeast populations. Done right, a starter can be a great thing, but done wrong you might only break even or worse, reduce your yeast count. The only real benefit is conditioning the yeast to metabolize your wort, but this is generally only going to make a different in high gravity ales. If you're not super careful, or don't have a stir plate and a complete yeast nutrient, it turns out that you're safest just following the manufacturers instructions.
Rehydrating yeast is a similar story. You're creating more chances to shock the yeast and more than likely the quality of the cells is degrading while they are being rehydrated. If you have really old yeast and you want make sure it is still viable, then this might save you from waiting several days to confirm that fermentation never started. But otherwise, it isn't boosting the cell count, and by having the yeast metabolize the little nutrients they were packed with while in water, you're more than likely making things worse. Also, use tap water if rehydrating. Yeast cells will degrade even more quickly in filtered or reverse osmosis water. The minerals in tap water are generally good for them (assuming your water is safe for drinking).
So, not what I expected there. I completely expected to find that, at a minimum rehydration would have no negative impact and a starter would always yield a bigger population. I was humbled and very incorrect.
As far as pitching rates, this was another surprise. When in doubt, most people seemed to recommend over pitching. When I went out and did the research things made a lot more sense. Spoiler: if you're not confident you can hit the perfect value, under pitching is better (again, high gravity ales excluded).
The article basically made the point that yeast don't care about making beer. They care about themselves and they will react based on the current conditions. Ideally, they want to procreate, but they also want to live. What is usually considered the ideal pitching rate involves attempting to make a situation where the pitched yeast will reproduce a little, but spend most of their time making alcohol.
The ways a brewer controls this are with the initial yeast population and the gravity of the wort. If there is a smaller population and a lot of resources, the yeast will spend more time procreating. If the yeast population is higher relative to the resources available, then they will spend their time subsisting and creating your beer. The ideal pitching rate then is designed to allow just enough new cells to be born to carry your beer to the finish line while allowing the yeast to be as comfortable as possible.
What this ends up meaning (and this is partially dependent on personal preference) is that in most cases you want to under pitch if you aren't sure about yeast cell counts. Both over and under pitching result is greater attenuation, but over pitching creates a battle for resources which in the best case just results in stressed yeast and mild off flavors, but in the worst case can lead to yeast death and much worse off flavors in your beer.
Under pitching on the other hand might lead to a slower starting fermentation but it will also lead to a greater population of younger, healthier cells. Hence the reason under pitching also results in better attenuation than the ideal pitch rate. You end up with a bigger population of cells more capable of taking the fermentation process further. This also means it is less likely that you'll need to re-pitch at bottling time. In fact, only over pitching or waiting far too long to bottle should lead to the need for re-pitching at bottle time.
The other reason to prefer under-pitching is that you can always add more yeast later, but you can't easily remove them.
So, this ended up being another great topic because it stresses two things I tend to aim for; simplicity and cost efficiency. If you're just getting started, don't listen to the forums. Follow the directions for your yeast, which might be as simple as dumping a dry packet in the wort. Also, if your yeast pack says it can handle 5 gallons, don't feel the need to pitch a second just because a forum suggested it. If you have problems with yeast getting started on a particular recipe you can always pitch more, and consider pitching double if you do that recipe again. It is really that simple.
Also, as far as pitching rates are concerned. As I pointed out, BeerSmith and many other tools will just round up to whole numbers of packs. Since most yeast packs and their directions are intended for 5 gallon batches, if you're doing that size of a batch and you pitch 2 packets you're very likely to go nearly as far as doubling the ideal pitch rate. A single pack on the other hand will usually result in just slightly less than the ideal rate. In other words, safer and closer to the ideal pitch rate.
Before I dive in, if you're making a high gravity beer, pretty much everyone is in agreement, do everything you can to improve odds as these are most at risk of a stalled fermentation. And in these cases a starter may actually make sense. Or even better, pitch onto a yeast cake from a lower gravity beer. But, as a general rule for more regular strength beers, I think what I'm going to say makes sense.
Preparing yeast beyond dry pitching takes time. Which means I definitely wanted to understand the benefits, if any. Rehydrating yeast wasn't affecting me much. I simply take the yeast out when I start brewing and pitch it into a cup of room temperature water while the wort is cooling, which takes 30+ minutes in my bath tub anyway. But, nonetheless, even that seemed pointless. After all, if it isn't a high gravity wort, you're not really doing anything that won't happen when you pitch dry anyway.
I didn't keep the link, but in my research I stumbled across an article where an individual did some test batches with different pitching rates and another article where yeast preparation was discussed. And the results were actually quite interesting.
As far as prep goes, making a starter or rehydrating actually run the greatest risk of hurting your yeast populations. Done right, a starter can be a great thing, but done wrong you might only break even or worse, reduce your yeast count. The only real benefit is conditioning the yeast to metabolize your wort, but this is generally only going to make a different in high gravity ales. If you're not super careful, or don't have a stir plate and a complete yeast nutrient, it turns out that you're safest just following the manufacturers instructions.
Rehydrating yeast is a similar story. You're creating more chances to shock the yeast and more than likely the quality of the cells is degrading while they are being rehydrated. If you have really old yeast and you want make sure it is still viable, then this might save you from waiting several days to confirm that fermentation never started. But otherwise, it isn't boosting the cell count, and by having the yeast metabolize the little nutrients they were packed with while in water, you're more than likely making things worse. Also, use tap water if rehydrating. Yeast cells will degrade even more quickly in filtered or reverse osmosis water. The minerals in tap water are generally good for them (assuming your water is safe for drinking).
So, not what I expected there. I completely expected to find that, at a minimum rehydration would have no negative impact and a starter would always yield a bigger population. I was humbled and very incorrect.
As far as pitching rates, this was another surprise. When in doubt, most people seemed to recommend over pitching. When I went out and did the research things made a lot more sense. Spoiler: if you're not confident you can hit the perfect value, under pitching is better (again, high gravity ales excluded).
The article basically made the point that yeast don't care about making beer. They care about themselves and they will react based on the current conditions. Ideally, they want to procreate, but they also want to live. What is usually considered the ideal pitching rate involves attempting to make a situation where the pitched yeast will reproduce a little, but spend most of their time making alcohol.
The ways a brewer controls this are with the initial yeast population and the gravity of the wort. If there is a smaller population and a lot of resources, the yeast will spend more time procreating. If the yeast population is higher relative to the resources available, then they will spend their time subsisting and creating your beer. The ideal pitching rate then is designed to allow just enough new cells to be born to carry your beer to the finish line while allowing the yeast to be as comfortable as possible.
What this ends up meaning (and this is partially dependent on personal preference) is that in most cases you want to under pitch if you aren't sure about yeast cell counts. Both over and under pitching result is greater attenuation, but over pitching creates a battle for resources which in the best case just results in stressed yeast and mild off flavors, but in the worst case can lead to yeast death and much worse off flavors in your beer.
Under pitching on the other hand might lead to a slower starting fermentation but it will also lead to a greater population of younger, healthier cells. Hence the reason under pitching also results in better attenuation than the ideal pitch rate. You end up with a bigger population of cells more capable of taking the fermentation process further. This also means it is less likely that you'll need to re-pitch at bottling time. In fact, only over pitching or waiting far too long to bottle should lead to the need for re-pitching at bottle time.
The other reason to prefer under-pitching is that you can always add more yeast later, but you can't easily remove them.
So, this ended up being another great topic because it stresses two things I tend to aim for; simplicity and cost efficiency. If you're just getting started, don't listen to the forums. Follow the directions for your yeast, which might be as simple as dumping a dry packet in the wort. Also, if your yeast pack says it can handle 5 gallons, don't feel the need to pitch a second just because a forum suggested it. If you have problems with yeast getting started on a particular recipe you can always pitch more, and consider pitching double if you do that recipe again. It is really that simple.
Also, as far as pitching rates are concerned. As I pointed out, BeerSmith and many other tools will just round up to whole numbers of packs. Since most yeast packs and their directions are intended for 5 gallon batches, if you're doing that size of a batch and you pitch 2 packets you're very likely to go nearly as far as doubling the ideal pitch rate. A single pack on the other hand will usually result in just slightly less than the ideal rate. In other words, safer and closer to the ideal pitch rate.
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