Is there any way to keep the yeast going to use in the next batch so you don’t have to buy it every time?
Absolutely! Brewers, small and large, have been re-pitching yeast for as long as beer has been brewed. Brewing scientists did not describe the basics of fermentation until the mid 1800s, and Emil Christian Hansen did not develop pure culture methods for brewing yeast until the 1880s. This means that for thousands of years, beer was made using a mystical and unknown ingredient that could only be introduced to wort through re-pitching methods! Of course, the beers before modern microbiology were probably much different and the advances in brewing microbiology advanced the spread of lager beer across the globe.
The basics of yeast harvesting and re-pitching are really quite simple. Yeast from clean fermentations is collected, cleaned, stored, and re-used within a reasonable time frame. A variation on this same process is to clean, collect, store and re-use. So how do you do this at home?
The simplest methods of yeast cleaning attempt to remove trub, hop matter, and dead/low viability yeast cells from the yeast crop that we want to collect and use. Many brewers use some sort of skimming method to remove trub from the top of the fermentation. A blow-off tube in a carboy actually serves this purpose and does a very good job of removing trub during fermentation. Skimming can also be performed manually in open fermenters using a slotted spoon to remove the dark brown foam, sometimes called braun hefe (brown yeast) or brand hefe (burnt yeast), from the top of the yeast kräusen. Top skimming removes cold break trub and very bitter hop acids that stick to yeast cells and rise to the surface of the fermenter. If these compounds are not removed by top skimming, much of this stuff falls to the bottom of the fermenter.
Racking beer into a secondary immediately following primary is another example of yeast cleaning as this method leaves behind trub, hop particles, and early-flocculating yeast cells. If you are using a carboy as your fermenter, you can harvest the yeast after the carboy has been emptied by simply swirling the yeast off the bottom with the small amount of beer remaining in the carboy, and then pouring the slurry into a container for re-use (more on this later). It is not advisable to harvest yeast from the bottom of a fermenter weeks following fermentation and yeast flocculation because yeast viability declines during this time period.
Conical fermenters are becoming more common among homebrewers these days, and these vessels allow trub, hop particles, and early-flocculating yeast to be purged from the bottom before the prized yeast cells flocculate, thereby eliminating the need to rack to a secondary. In practice, many brewers blow the cone about 24 hours after the fermenter is filled to remove cold break trub and dead cells, and also discard the first bit of yeast drawn from the cone immediately prior to harvest because this yeast is a combination of dead/low viability cells and early flocculating cells that are not the best to select for the next fermentation. Note that some yeast strains are aggressive top-croppers, for example most hefeweizen strains, and either need to be harvested from the top of open fermenters, vacuumed off the surface of a closed fermenter (see my June 1996 landmark BYO article “Fermenting with your Vacuum Cleaner: Offbeat Tips”) or collected from the bottom of the fermenter after the beer has been drained from the bottom.
Some commercial brewers clean their yeast after harvesting by using a screen to remove trub and hop particles (you can do this at home using a hand held stainless strainer often used to remove pulp and seeds from citrus juice or cheese cloth), and some brewers use water washing to remove as much beer from their harvested yeast prior to storage. Regardless of the cleaning method, it is important to harvest yeast soon after fermentation is complete because yeast viability declines when yeast sits at the bottom of the fermenter, especially if the fermenter is not kept cold.
If you read brewing texts written for commercial brewers, you will read about acid washing as a method used to kill bacteria. Most commercial brewers these days have moved away from acid washing for a number of reasons, the primary reason being that modern equipment is easier to keep clean and the incidence of bacterial growth has greatly reduced over the past 30 years. Acid washing also decreases yeast vitality and can decrease viability if not performed properly, which is another reason that many brewers avoid this form of chemotherapy for harvested yeast. I do not recommend acid washing because I believe that the risks to yeast viability and vitality greatly outweigh the benefits when the basic rules of yeast re-use are followed.
After yeast has been cleaned and harvested, it is now time for storage. The two most critical things to control during yeast storage are time and temperature. If you are able to keep yeast between about 28 to 34 °F (-2 to 1 °C), you can easily store your yeast slurry for up to about 2 weeks without excessive loss of viability. Of course, minimizing storage time is preferable because cropped yeast works best immediately after harvesting. The normal practice for many commercial brewers is to hold yeast for no more than 3-4 days, often times agitated to minimize temperature gradients in the slurry, because the risks to the brewery are much greater on a larger scale. One trick to keeping yeast cold is to make a salt water and ice mixture that you can dunk your yeast container in, and storing the entire kit in a refrigerator; if the salt water mixture is contained in an insulated container, the low temperatures can be maintained for a very long time.
Whatever you do, DO NOT store your yeast slurry in a sealed jar! Yeast cells contain glycogen and there can be low-level metabolic activity even at very cold storage temperatures, resulting in the production of carbon dioxide and the potential for exploding yeast bottles. I actually caused such an explosion about 25 years ago by placing a Pyrex media bottle with yeast slurry and a tightly attached lid in a walk-in cooler in the brewing lab at UC-Davis. Fortunately, there was no one in the cooler when this bottle exploded!
Although the cell density in cropped yeast slurry varies by strain and by batch, the density is usually between 750 million and 1 billion cells per milliliter, which is really a pretty tight range when compared to the pitching rate range that is needed to produce great beer. Yeast viability does drop over time, but if you are able to keep your slurry cold OR minimize storage time you don’t need to worry too much about viability. This means that you don’t need to buy a microscope to perform cell counts and to do viability tests to successfully re-use yeast at home. A general rule of thumb pitching rate is 12 million cells per mL, and can be obtained by adding 250 mL (1 cup) of slurry to 5 gallons (19 L) of wort at 12–14 °Plato (1.048–1.057 SG); textbook pitching rates are proportional to wort strength, so you can scale up or down depending on gravity.
There are some basic rules about selecting yeast to re-pitch, and here are my top 5:
1. Never re-use yeast from a batch that fermented slowly or abnormally.
2. Never re-use yeast from a batch that tastes off.
3. Never re-use yeast from beers with an original gravity greater than about 16 °Plato/1.064 SG (this rule is often broken by breweries who brew primarily high gravity beers, and requires specific techniques to make successful).
4. Never re-use yeast slurry that has been stored for more than 2 weeks.
5. Never re-use yeast collected from spiced, flavored, fruit, or otherwise funky beer (mixed culture sours are excluded from this general rule).
Some brewers maintain a yeast culture like a sourdough mother. This is pretty easy to do if you have the proper ratio of yeast cells to food (one part yeast slurry to eight parts wort is typical). Other brewers like passing yeast around their brewing group; if you have brewing friends that you know well and trust, you can share yeast in an effort to minimize the time between collection and pitching. This can be fun, but is also pretty risky. I hope this information helps you in your yeast recycling endeavors!
Using normal homebrewing equipment, and cold crashing in the carboy within a chest freezer, what is the best way to avoid oxygen intake due to gas contraction and subsequent suction of airlock water and air into the carboy?
I feel like this is a stumper of a question because it is nearly impossible to avoid oxygen from flowing into a carboy when the carboy is placed into a cold environment. But preventing liquid suck-back is pretty easy to avoid. This is a question I have answered several times over the years, and is one of those important questions that can never be answered too frequently.
So to recap the problem; when gas cools it contracts and creates a suction in a closed container. Carboys are vented using airlocks and the liquid in the airlock is pulled into a carboy when the gas cools. The best way to prevent suck-back is to simply remove the airlock when cooling, but this results in exposing your beer to oxygen and microorganisms in the environment. Cotton plugs are great filters used in microbiology labs to keep microbes from the air out of flasks and test tubes, and work very well for the application in question. Simply remove your airlock, insert a large cotton plug made from a roll of cotton batting available at your local pharmacy, and move the carboy into the cooler. The only problem with this method is that air will be pulled into the headspace of the carboy as the gas contracts.
If the carboy were able to with-stand pressure, you could pressurize before moving into the cooler environment. But carboys are not designed to hold pressure so this method cannot be used. You can, however, blanket the headspace with a very slow flow of carbon dioxide and vent the gas through the cotton plug or airlock. Once the carboy headspace is the same as the cooler temperature you can stop the carbon dioxide purge (or not if you are not purging) and reinstall the airlock.
I am a fan of Corny kegs for secondary because they are so convenient to use, and because they are pretty cost-effective for the benefits they offer. If you have a Corny keg, you can rack your primary into the keg, apply top pressure to the keg, and throw it into your cooler without having to worry about suck-back, carbon dioxide purging, or over-pressurization.
Is there a good reason to drain off the liquid in a yeast starter before adding the cells to your wort?
The liquid above the yeast sediment in a starter is beer, and this beer usually does not taste much like the beer that is produced after the yeast cells from the starter are used for fermentation. This is the main reason that some brewers would rather leave this beer behind and only use the yeast from the starter.
The problem is that it is best to transfer yeast from the starter to the fermenter about 48 hours after the beginning of the starter fermentation (or 48 hours after the beginning of the last step of a multi-step propagation if you are doing that), and the yeast has not yet flocculated. And if you wait long enough for the yeast to flocculate the yeast will be less vigorous when pitched into your fermentation. So in practice, most brewers pitch the entire starter into the fermenter.
A beer made using freshly propagated yeast is referred to as “first generation beer” because it is made from first generation yeast. The yeast harvested from a first generation beer is referred to as second generation yeast. First generation beers often taste different from subsequent generations. These latter generation brews do not contain “propagation beer” in question which many larger breweries will blend with older generation beers. I have always found this distinction to be interesting because many homebrewers only brew beers from first generation yeast, and most commercial brews are brewed from “older generations” (most lager brewers limit their yeast to about 10 generations, and ale brewers usually run up to 20 generations or greater) since each fermentation produces enough yeast for 2-4 more batches.
Considering that caramel malts have their starches converted to sugars by heat inside the husk during Malting and do not have to be mashed, are caramel malts (when mashed) affected by mash temperatures in the same way base malts are in terms of the activity ranges of the diastatic enzymes? In other words, would mashing caramel malt in the range of 140–148 °F (60–64 °C) yield a higher degree of attenuation than mashing it in the range of 150–160 °F (66–71 °C)?
Van Buren, Arkansas
This is a question that I cannot remember ever being asked and am scratching my head a bit! Your description of caramel (also known as crystal) malt production is right on target, and the assumption is that there is no starch remaining after these malts are produced. The term “starch conversion” is really quite vague since conversion does not give any information about fermentability, and really just lets the brewer know if there are any amylose fragments large enough to react with iodine in the iodine test. No iodine reaction, and we say that the starch has been converted, but converted to what?
So what do we know about the mash that occurs inside of the malt kernel in the “stewing” phase of crystal malt production? Well, we know that there is not an excess of water as there is during mashing in the mash tun. Very thick mashes with less water do not behave like thinner mashes. My guess is that there is some residual starch present in crystal malt because there is not enough water to hydrolyze all of the starch, which is different from a typical mash.
Another assumption made about crystal malts is that the sugars and the amino acids are all tied up in Maillard reaction products and unavailable to malt amylases. While it’s true Maillard reaction products are not available to malt amylases, all of the carbohydrates in crystal malt cannot be bound to amino compounds because there is more carbohydrate in malt than amino compounds (amino acids, polypeptides, and proteins).
Your mashing temperature does indeed affect residual starches present in crystal malts. But this statement comes with a very big caveat . . . there is usually so little starch left in properly made crystal malt that the concentration is effectively zero. And since crystal malt usage rates rarely exceed 15%, the mash profile as it pertains to crystal malt starch degradation is really more of an academic pursuit than anything. The fact that so much great beer is made by steeping crystal malt with no mash modification at all, reinforces this notion.
Crystal malts and roasted grains are usually lumped together into the “steeping grains” category of ingredients. Steeping grains are thought to be unaffected by mashing because the nature of the grain endosperm has been changed so much during production that malt enzymes active during mashing do not alter the extract produced from these “steeping grains.” However, not all specialty malts are created equally and there are differences in quality and consistency among suppliers, and sometimes within an individual supplier.
One thing that can yield interesting results is to take 50 kernels of malt from a bag, carefully cut each kernel in half with a razor blade, and observe the appearance of the endosperm. Crystal malts should have a uniform, crystalline appearance. Different crystal malts will have different colors depending on the color specification, so this difference is expected between different samples.
The look that is not expected in crystal malts, independent of supplier and color specification, is a starchy appearance that is similar to the endosperm of pale malts that require mashing (cut a few kernels of a base malt for reference). Starchy “crystal malt kernels” are, despite the label on the bag, not actually crystal malt kernels. If you happen to be using crystal malt with a high proportion of starchy kernels, then this whole topic changes pretty dramatically because steeping these kernels will contribute starch to your wort. Not a big deal if you are an all-grain brewer and mash all of your grains together, but this could be a big deal to extract brewers using steeping grains.
Mash temperature does, without question, influence wort fermentability. Crystal malts increase residual extract, and add body, color, and mouthfeel. These desired effects are independent of wort fermentability associated with the base malt starch and enzyme package. If you are brewing a beer with crystal malts and want to increase fermentability, you can adjust the mash profile to affect the base malt starches or you can dilute residual extract with sugar adjuncts. Thanks for the interesting question!