Round It Up! Collecting Yeast from Bottles
Have you ever thought about getting yeast from a bottle of beer? Wouldn’t that be a great way to start brewing traditional beer styles? It can be, but as anyone who has ever tried to collect yeast from bottles will tell you, it can be a hit-or-miss affair. Well, cheer up. Collecting yeast from bottles is tricky, but the following tips just might help you achieve some success.
All beer is made by yeast. We let bacteria ride along in a few styles, but without yeast, there would be no beer. Yeast cells consume wort sugars and convert them into alcohol, carbon dioxide and flavor compounds. In some beers, the yeast is left in the beer when bottling. A successful “yeast rancher” can sometimes recover this yeast for use in homebrewing.
Why is yeast left in the bottle? It depends on the brewery. Some German hefeweizen brewers bottle with yeast as a matter of style. Some do it to enhance shelf life, and many breweries do it for cost. Breweries save money by not filtering the beer because it is one less step, and filtering material and equipment costs money.
Most homebrewers “bottle condition” their beer without thinking about it. Bottle conditioning means carbonating beer naturally in the bottle with a bit of priming sugar and yeast. Since most homebrews are not filtered, they always have some yeast in the bottle. Even filtered beer can have some yeast in it. But it is hard to cultivate small quantities, and most likely you will be unsuccessful unless you have a well-stocked laboratory at your disposal. If the beer is pasteurized, your chances are extremely slim, since even if there were some cells left after filtering, they would have been killed by the pasteurization process. All canned beer is pasteurized.
Even when beers are bottled with yeast, it can be troublesome to collect live yeast. Sierra Nevada, for example, filters their beer and then adds yeast back when bottling. The yeast is added in order to develop natural carbonation in the bottle, rather then using compressed carbon dioxide. Many brewers feel this gives a better flavor to the beer. But the quantity of yeast added to the bottle is very small; indeed, many drinkers do not even notice the small yeast film at the bottom of the bottle. Many homebrewers have tried to obtain yeast from Sierra Nevada bottles, but have come up empty. Some of the reasons for that will be explored in this article.
What is the yeast condition in a bottle of beer?
Yeast is a single-cell organism, with an outer cell wall for rigidity and protection and a hydrophobic plasma membrane to create a barrier to water. As yeast sits in a bottle of beer, it will slowly strip the beer of any trace minerals and elements, even consuming some residual sugars. Once these components are gone, yeast will resort to feeding off dead cell material.
The danger of bottling with yeast is that it can provide nutritional value for bacteria and wild yeast to build in numbers in the bottle. The advantage is that they provide a natural oxygen scrub, in that they will consume any oxygen introduced during the bottling process. (Oxygen is evil number two to bottled beer. Bacteria is number one.) But it takes only very limited amounts of yeast to do this. You will notice that the pH will rise over time for bottled-conditioned beer. This is a result of cell lysis (death) and release of alkaline compounds into the medium.
What causes cell death? Alcohol, pressure (the build-up of carbon dioxide), temperature, handling, contamination with other microorganisms, and time are some factors. The more alcohol in a beer, the higher the proportion of cell death that will occur. Take a Belgian beer like Chimay, for example. Here you have a high-alcohol beer, combined with the fact that it was made in Belgium, shipped and imported, which takes time. Many imports are six months old (and sometimes much older), before being consumed. That is a very long time for yeast to sit in a high-alcohol environment.
In addition to cell death, living yeast can mutate during storage. Mutations happen when fragments of yeast DNA rearrange. Mutations are constantly occurring in brewers yeast DNA, but since brewers yeast has multiple copies of each chromosome, the mutations usually do not show an effect. But as mutations build up over time, they start to become noticeable in the yeast population. What types of mutations occur? You name it, but the most common mutations are flocculation changes, attenuation changes, petite mutants and flavor changes.
What causes mutations? The same reasons as for cell death above, but much more difficult to identify and quantify. Stress of any kind will cause yeast to react and can create mutants. Temperature change (either up or down), is one example of a stress on yeast that induces mutations.
The take-home message is that you should not expect yeast from a bottle-conditioned beer to perform exactly the same as it did at the original brewery. It is almost impossible to get commercial-grade quality yeast from bottle-conditioned beer, but you can get some nice, diverse yeast to use in a few homebrew batches.
Sources of bottle yeast
There is much speculation as to what yeast strain is used in a particular bottled beer — and most breweries try hard to protect this proprietary information. Sometimes a brewery will bottle their beer with a different yeast strain than they used in the fermentation. Some breweries just say they do that, but actually bottle with their fermentation yeast.
European imports provide a wealth of yeast varieties, but they often suffer from age and handling. Some beers that are bottle-conditioned for the European market are pasteurized before being shipped to North America, to increase their shelf life.
The beers that most homebrewers are interested in collecting yeast from are Belgian beers and hefeweizen beers. German-made hefeweizen beers are typically filtered, and lager yeast is added back at bottling. This not only keeps a primary flavor component out of the beer and away from yeast-stealing competitors, but it improves the shelf life by preventing the continual development of phenol and clove character to the beer during storage.
Some Belgian beers are bottled with the original fermentation yeast. But in many cases the fermentation yeast is a mixture of strains. Often, there is an unintentional mixture of strains, meaning wild yeast contamination. Chimay is one beer that sparks a lot of debate about what yeast is in the bottle. It is in fact bottled with the primary fermentation yeast, but the yeast is no longer the same when collected out of the bottle (for some of the reasons stated earlier). That is probably why many people who have collected it, and used it, think that it is not true Chimay yeast.
Microbreweries are probably the best source of bottle-conditioned yeast. They will be the freshest, and usually have fairly high levels of yeast in the bottle. But many microbreweries do not have the money to invest in high quality bottling lines, so the level of contamination can be high at times.
There are many Internet discussion groups that attempt to assemble information on bottled-beer yeast identities. They are a decent resource, but remember that some of it is speculation and even accurate information can change at a moment’s notice. A brewery may decide to start bottling with a different yeast or eliminate bottled yeast entirely. Your only sure bet is to collect some and try it out.
How do you get yeast out of the bottle?
Refrigerate the bottle for at least two days to get a nice yeast sediment in the bottom. Remove the bottle from the refrigerator and sanitize it, especially the rim area. Also sanitize a beer glass, a yeast collection vessel (a 50 mL test tube works great), and the surface you are working on.
It is best to have some 70 percent isopropanol (available in most drug stores) around to spray on surfaces. Remove the bottle cap with a sanitized opener, and pour the beer into a sanitized glass. Stop pouring when you get close to the sediment, and without tilting the bottle back up, swirl to stir up the yeast and add to your sanitized collection vessel. Cap and refrigerate if not using the same day. It will last for a couple of weeks in your refrigerator.
If you are successful at collecting yeast from a bottle, how do you know for sure that is not contaminated, and how do you know if it will work? Collect some and do a test batch.
What do you need to do with bottled yeast?
Collect it, test it, clean it up if necessary, and grow it up to the quantity you need. Here’s how to proceed.
Once you have yeast in a collection jar, it should be tested. This can be done by simply inoculating 50 mL of wort with a very small portion (less than 5 mL) of the sample, allowing it to ferment for five days and tasting the final product or plating the yeast out on petri dishes. The plating technique has been covered in previous articles, including “Culture in Your Kitchen” (March 2001). It will be summarized here to be complete. Plates and slants are commonly used in all yeast and bacteria culturing. A semi-solid media (generally just called agar) is put into a petri dish or test tube. If it is a petri dish, it is called a plate, and if it is a test tube, it is called a slant. Slants are used for long-term storage (less than six months), and plates are used to work with yeast for the short term. For isolating yeast from bottled beer, plates are used. If you want to store the yeast after isolating it, it can be put on slants. Slants have a longer shelf life because they have a screw cap and don’t dry out.
To plate a yeast sample collected from a bottle, dip a sterile inoculation loop into the yeast and streak it across the agar on the plate. Plates provide a check at the purity of your yeast, because most contaminants can grow and become a visible colony. This allows the average person without a high-power microscope to identify contaminants with the naked eye. It will show if there is bacteria in the sample. Bacteria can appear translucent or slimy with a clear, white or reddish-pink tint. Molds are easily spotted; they look like the mold that grows on bread.
You can also look at the different yeast colonies and evaluate whether they all look the same, or have major differences. Different colony types usually indicate different yeast strains. If there are different types, you can put each one separately into 50 mL test batches, and taste the result.
After inoculating small test batches, how do you choose the desired yeast? Choose the yeast that tastes and performs the best. A good indicator of wild yeast, for example, is little to no change in the specific gravity of the beer. That is why you want to test the yeast. You don’t want to invest in ingredients for five gallons of beer, only to get a problem fermentation. Or perhaps the original fermentation culture was mixed; if you think that’s the case, you might want to use 2 or 3 different strains from your separation.
Once you are confident the yeast is pure and of good brewing quality, it needs to be cultured to a volume for your brew batch. Healthy yeast grow in globs or in single colonies as round, creamy-white domes on the agar. Blisters around a colony can be a sign of wild yeast. Each colony contains millions of cells.
For a five-gallon batch of beer, you need at least 10 billion cells total. A 16-ounce bottle of beer will only have 1 to 500 million total cells. While it can sometimes work to do a one-stage starter from a bottle of beer, it is best to do at least two stages (10 mL and 400 mL, for example; see below).
The following steps should be followed when building up the yeast cell count in two stages:
- Plate the yeast from the bottle of beer as described above.
- Pick a single colony (small white disc of yeast) from plate and transfer to 10 mL of sterile wort in a test tube, being careful to open containers for the minimal time.
- Prior to inoculating starter, flame opening, then insert loop with yeast and shake yeast into solution. Flame cap and tube, then snug cap. Unscrew cap slightly to allow oxygen transfer.
- Shake starter to aerate and to mix yeast into suspension. Leave upright in a warm place (70 to 80° F). Your 10mL starter is now inoculated and will grow over a period of 24 to 48 hours. It won’t look like a normal fermentation; very little action will be seen at the top. Rather, a white sediment of yeast will appear on the bottom over the next two days, assuring you that growth has occurred. You should use this starter after approximately two days, however, it will keep if refrigerated after growth has occurred up to 7 days. Just remember to warm it to room temperature before proceeding to the next step.
- When you are ready to grow your starter, boil 400 mL of water with 4 tablespoons of dry malt and some dry yeast nutrient. Add mixture to your sanitized Erlenmeyer flask. If you use a 1 liter Erlenmeyer flask, you can boil directly in the flask. If you use a 500 mL flask, it is preferable to boil separately, in order to avoid boilover.There are two acceptable methods of sanitizing your flask. You may make up a chlorine solution of 1 tsp. bleach, add to Erlenmeyer and fill to top with water. Allow flask to soak for 15 minutes. Rinse with hot water, then cap top with aluminum foil.
Another method of sanitation is to place the flask, with a foil cap tightly molded around the lip of the flask, in the oven at 350° F for 2 hours. The bake method is preferred and may be done days in advance.
Once you have filled the Erlenmeyer with your hot boiled media, quickly place foil over the top, creating a cap. Allow to cool to room temperature, or cool to touch. You are now ready to add the 10 mL starter to the Erlenmeyer flask.
Tighten cap on 10 mL vial and shake to re-suspend yeast into solution. Unscrew cap slowly as there may now be pressure in the 10 mL vial, then flame opening while removing foil cap from flask. Flame opening of flask and dump in 10 mL vial, quickly replace foil and form tightly around opening. Shake Erlenmeyer flask to aerate and to mix yeast into solution.
- Allow this to sit at warm temperatures (about 70° F) for 1 to 2 full days before use. Activity should be present within 12 to 24 hours. Again, activity will only be slight and will not produce the vigor of a five-gallon fermentation.
- After 24 to 48 hours, swirl flask to mix the yeast into solution, remove foil, flame lip of flask and pour into five-gallon batch. Shake fermenter to aerate, then leave at recommended temperature. Activity should be present in 6 to 24 hours.
- Ferment ales at 65 to 70° F, and lagers at 48 to 55° F.
Summary: Life on the ranch
A common technique among homebrewers is to simply take yeast sediment from the bottle and put it into a pint of wort. Theoretically the yeast grows up, and you can use it to make five gallons of beer. However, several problems can arise. First, if the beer has very little yeast in it (like Sierra Nevada Pale Ale), there may be very few live cells by the time you try and collect it. So the result is little to no activity in the pint starter. The other problem is mutated or contaminated yeast from bottles.
By plating the yeast out on agar petri dishes, you can assess the quality of the yeast before using it, and it gives you a chance to clean up a contaminated sample. You do this by carefully selecting health colonies with your loop and leaving bacteria and contaminants behind. By giving the yeast a test drive in 50 mL wort sample, you can taste whether you should continue. Of course, you could taste the pint starter as well.
Collecting yeast from bottle-conditioned beer can be a fun way to experiment with different yeast strains. If you know the type of yeast in the bottle, it can also be a good way to produce traditional beer styles. It can be done easily, but you can increase your chance for success by checking the yeast first. Good luck!
