What do home brewers and industrial brewers have in common?
They all create wort and pitch yeast to make beer. The processes used may be different, but the one constant thing is “yeast.” Without it, beer production wouldn’t be possible.
Yeast is the most important part of fermentation. This little microbe is the cornerstone of how beer tastes, smells and gets one inebriated. Hence, harvesting and repitching yeast is a common practice in many breweries.
Professional brewers reuse yeast all the time, mainly because the cost of yeasts can be prohibitive in large batches. Brewers can reuse yeast for up to 10 generations if good yeast harvesting and storage practices are followed.
This article will discuss the best and worst yeast harvesting practices for breweries. But first, a quick primer on yeast harvesting.
What Is Yeast Harvesting?
Yeast harvesting is the process of culturing yeast from a previous batch, yeast pack, or bottle to build up the cell count and pitch it again.
By harvesting and reusing yeast, brewers can save money and even become familiar with a particular strain—what flavor it produces, its standard flocculation rates, what temperature it likes, and its normal fermentation time frame, among other things.
Harvesting can be done by either top cropping (open vessels) or bottom cropping. With the advent of cylindro conical fermenters, bottom cropping has become the norm and is considered the best harvesting method for breweries.
Yeast Harvesting Best Practices
As mentioned earlier, the best yeast harvesting methods can generate up to ten generations from one initial purchase. Here are the best yeast harvesting practices to follow.
1. Harvest at the Right Time & Temperature
The timing of cropping impacts the quality and density of the slurry. So, it’s critical to maintain consistent timing to help keep the desired characteristics of the culture.
In bottom cropping (Dish Bottom Vessels and Cylindroconical tanks), harvest yeast:
- Shortly after fermentation finishes
- When the beer temperature has fallen below 40 °F (4 °C), typically within 48 hours
- After the trub has been fully discharged.
In an open vessel (top cropping), harvest yeast:
- When the gravity has dropped below 50%
- Only if the slurry looks creamy with no trub, off-flavors, or aromas. Watch out for stuck fermentations and fix them once they happen.
2. Know Which Part of the Yeast to Extract
Yeast is usually cropped from the bottom of the conical fermenter cone after fermentation and cooling to ensure fermentation has completed and cells have flocculated out of the beer and sedimented at the bottom.
This process produces “3 layers” within the yeast cone, which must be managed.
- Layer 1: Trub or dead yeast (at the bottom)
- Layer 2: Ideal and healthy yeast (in the middle)
- Layer 3: Poor flocculating and thin yeast (at the top)
The best yeast cells to harvest settle in the middle layer. This is the section of the cone you’ll harvest. The middle layer is composed of healthy yeast and dense culture, which is fit for fermentation.
3. Reuse Yeast for 5 – 6 Batches
Under perfect conditions, brewers’ yeast can be reused indefinitely.
But in the real world, conditions change each time you harvest yeast for the next brewing cycle. Even minor changes can stack up to the point where the beer loses its flavor or won’t be the same as the first batch.
As such, experts recommend you reuse the yeast for 5 – 6 batches and not more than ten.
The more you reuse the yeast, the bigger the variance you’ll see from the original batch. Plus, there’s always the risk that some wild yeasts or bacteria will creep in with each new generation. This may not be a problem for home brewers doing it as a hobby, but a lack of consistency can be a major problem for breweries.
4. Yeast Storage Best Practices
Yeast should be used as soon as possible and not stored for long periods before reuse. There are many options for yeast storage vessels (also known as brinks). A brink can be as simple as a bucket or a keg modified for pitching.
Whatever yeast vessel you choose, make sure it’s easy to clean and has a way to relieve pressure when yeast is stored.
When it comes to yeast storage, the following practices should be observed:
- Always store yeast in cold temperatures. The ideal temperature range is about 33˚F-38˚F. Try to keep the yeast as cold as possible but never let it freeze.
- The storage vessel should have as little oxygen as possible
- Store it in a sterile container.
Before using a yeast storage vessel, disassemble and soak the fittings to wipe out any bacteria and purge the vessel with CO2 to minimize the slurry’s contact with oxygen.
The Dont's of Harvesting Yeast
Avoid these practices when harvesting yeast.
1. Storing Yeast in the Fermenter
Storing yeast in the fermenter is not recommended.
Note that yeast has been found to contain insulating properties. Hence, if stored in the fermenter, the middle layer of the yeast cake that forms at the bottom of a cylindroconical fermenter can heat up. And when yeast temperature rises, its life expectancy falls.
2. Filling the Brink to the Top
When harvesting, you need a vessel to hold the yeast—commonly called a brink.
Never make the mistake of filling your brink to the top when cropping yeast. Yeast slurry is usually rich in CO2, which causes the yeast to expand and produce foam. As such, it’s recommended to leave an empty portion at the top to account for expansion/foaminess.
There you have it—the best and worst yeast harvesting practices.
By using the information in this post, any brewer should be able to harvest, store and reuse yeast utilizing the industry best practices. Yeast repitching, when appropriately applied, can reduce cost and tank time, which also results in greater operational efficiency.