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Yeast Washing - Tony Vacek (February 1998)
Get out the Bleach and Tide we all be going to get us some real clean yeasties. You betcha them litt'l criters are going to be spotless, squeaking clean and smell country fresh. Well, maybe something like that but not quite. When I started brewing several years back the first several kits I bought came with a package of dry yeast. It worked and I was happy with it. Then one day I ordered a Grand Cru that came with a liquid yeast vial. I felt that the taste was a step up over the prior batches that I had used dry yeast. Almost every batch since then has been fermented using liquid yeasts. Typically I would buy a yeast strain and use it for the batch at hand. I would then racked off the yeast and then send the yeast cake from my primary out to the septic system for its enjoyment. I was brewing about once a month and this didn't seem a waste of yeast. Besides the next batch I brewed might be a lager. Well times changed and thankfully I started brewing more often. About that time I thought that I needed to reduce the cost of brewing. The first item in my mind was to reuse the yeast. The cost of yeast is around five dollars and if I ran a second batch over the first batch's yeast I could spread that outlay over two batches. So planning of multiple batches using the same yeast was started at my brewery. When it was time to rack off into a secondary fermenter I had a second batch brewed to drop into the primary on top of the yeast cake that had formed. This also worked well in that I was doing multiple batches using the yeast where possible before switching to another yeast for a different type of taste. If you don't like putting your wort on the dregs how about this idea. You can siphon some of the yeast cake directly from the bottom of one batch into the new batch. Now my horizons are growing again. I don't want to run several batches of the same type back to back but I want to reuse the yeast. I currently do not want to start yeast ranching so it seemed like this yeast washing idea might be the way to go. Here's what I have found out.First off like so many items in homebrewing there are many different views on the proper way to do it. The concept is fairly simple. You want to remove yeast from a current batch with as little contamination as possible and save it in a sealed jar in the refrigerator until you are ready to pitch it again. Most breweries store their yeast in some fashion and repitch when needed. Why not us homebrewers.? If you are like me you like to brew a variety of styles with a variety of yeasts. This method of storing yeast should allow you to do this and still have the yeast available for a latter brew date. Why worry about washing the yeast? When Dave Logsdon of WYeast Labs was asked this question his answer was that it was important for healthy yeast to be washed free of trub and hop residue so that it could be stored for future use. Dave stated that the problem with simply storing the mixed contents from a carboy after fermentation was that the unwanted particulates would suffocate the yeast over a period of time. Also yeast washing allows you to remove the dead yeast cells from the sample. Most breweries, Dave stressed, use an acid wash. Now for us homebrewers the use of sterile water wash is much more practical. The water can be distilled or bottled but it must be free of chlorine.
Some advantages of the yeast washing process are that you have clean yeast in quart jar that is that is ready to pitch. This allows you to have more control over pitching rates. Each time you will know how much you are pitching verses just pitching on the yeast cake where each time the amount of yeast present differs. Some of the research was concerned that brewers pitching over the yeast cake may be overpitching the batch. I usually do not worry about this. I would see overpitching more preferable to underpitching. I have heard of brewers that have attributed problems with yeast bite to the practice of pouring fresh wort over dregs from the primary. Another benefit is that you will have less residual trub in your new beer, thus less potential off-flavor development. The washing process will yield a yeast mixture that will still get rapid starts, on the order of 10-12 hours and healthy fermentations. The biggest possible disadvantage that I found was as the number of generations increases the risk for mutation of the yeast also increases. You should keep this in mind in your brewing with washed yeast. But then again, think about the number of brews that you can pitch from the first yeast cake. If you get three or four jars of washed yeast from the first generation and then again from the second generation and then stopped. You would end up having gotten over 20 brews without going beyond the third generation. Not much worry about mutation of the yeast in only three generations. There is probably more worry about contamination in the processing. You need to remember that everytime you mess with the yeast there is an opportunity for contamination. So use good sanitation practices and you should have nothing to worry about.
Okay first we need to gather a sample of yeast to store. Where do we gather this from the primary or the secondary? Some say to use the secondary to get your sample. Why? How about the fact that the yeast from the secondary is cleaner than the primary. The trub is left behind during the racking from the primary. Others maintain the with the washing that you do this is not an issue. If you take your sample from the primary you are selecting the most flocculent and a more healthy yeast. If you consider that the secondary yeast has hung around in suspension from the primary. It is therefore less flocculent. If you repeatedly harvest yeast from the secondary to minimize trub carryover, then you are acting as a natural selection force and thereby causing your yeast strain to gradually become less flocculent. Then again the other side maintains that a benefit of using secondary yeast you will create select a more alcohol tolerant strain. If you are looking for a more non-flocculent varieties of yeast then perhaps the secondary selection would be the best route for you. Like I said there are different viewpoints you make the choice.
Now for the process....
First we need to get three one quart mason jars and sanitize them in preparation for the yeast slurry. Then we boil some water in a pot for 10 to 15 minutes and fill each jar half way with water. Seal the jar and allow them to cool. This can be done quicker by placing them in a refrigerator to aid in the cooling process. After they have cooled rack your beer to the secondary or to your bottling bucket depending on where you have decided to harvest your yeast.
We then should sanitize the opening of the carboy with flame or alcohol. You can flame-sterilize the mouth of your primary carboy by wiping it down with ethanol or rubbing alcohol and setting it on fire. It's not really dangerous. Please use some common sense and don't burn your house down or set your hand on fire. We would hate to lose any of our homebrewers. A couple of bucks for the alcohol and a spray bottle will be well worth the added safety against contamination.
Now pour the water from one of the quart jars into the carboy. Swish this around, and pour the watered down slurry back into the empty jar. Put the lid back on the jar and shake. Let it sit about 10-15 minutes, and you will see a whitish, maybe slightly tinted liquid of yeast and water separating from hops and other trub. While the viable yeast remains in suspension, pour off this portion into the second jar. Be careful to leave as much of the hops and trub behind as possible. Put the lid on and swirl the contents. Wait around 30 minutes. Then pour off yeast fraction which suspends above the particulate into the third container. Finally put the lid on and shake. Put this jar in the fridge. When this jar settles out completely (could be 1 - 5 days), you should have 1/4 inch to 3/4 inch of whitish yeast settled on the bottom, and what would appear to be beer as a liquid over this. You then store this container in a refrigerator until needed. This could be for one or several months before you begin to brew.
There is some concern that the yeast solution maintains a proper ph level for the yeast to survive and prosper during its hibernation in your storage jars. Numerous sources like Hough, Briggs, Stevens and Young, "Malting and Brewing Science" and Broderic, H.M. "The Practical Brewer" state that the pH should be between 2 and 2.8. Some of these sources warn that chemical washing "..represents a drastic measure which may affect the yeast and its brewing performance". There is mention that there is debate as to whether washing is a good idea or not but feel that it is OK if properly carried out.
When you are ready to pitch take the jar out of the refrigerator and let it come up to pitching temperature. You then pour off the liquid in the jar into your fermenter. The resulting fermentation will have a short lag time and is typically very active. Some sources recommend that a starter be made prior to pitching. This is probably not needed in that you've got a pretty decent volume of yeast already which should limit any chance of contamination. An advantage that I can see of using a starter is that it gives you is a chance to be sure that the yeast is still healthy. If you have followed the procedure the chances are extremely high that the yeast will be ready to go without a problem. Once again a choice that is up to you. Pitch directly or make a starter its your call.
Here is a the lazy mans or hobo's approach to yeast washing. How about just thinking of doing the washing? All you do is pour the sediment from the previous batch into a sanitized jar, then stick it into the fridge. Come pitching time, you just let it warm up to room temperature and dump it into the next brew as is. This has been done without any noticeable problems. I do not think I could recommend this one though.
We have mentioned that it was easiest for the homebrewer to use water but what else can be used? Some sources reference using substances other than water to wash the yeast. Such as DeClerk, J "A Textbook of Brewing", Chapman and Hall, London, 1957 briefly mentions washing with a 1:1000 solution of phosphoric acid to kill any lactic infection. The use of carbonated water is not appropriate. If you think about it the yeast have already been washed in the fermenting beer which is saturated with CO2. This will not give the desired effect, however, since the pH of fermenting beer is typically in the 4.5 - 5 range. The desired pH for yeast washing is a pH of around 2 is desired. When you saturating water with CO2 at atmospheric pressure will result in a pH of no lower than 4 since not enough CO2 can dissolve to get it lower than that. Raising the pressure will lower the pH somewhat but it would obviously be impractical to carry out the wash under pressure. Phosphoric, citric, tartaric and sulfuric acids seem to be the most popular other solutions for yeast washing. If you do use phosphoric acid you have to be careful since it can hamper the yeast and could possibly kill them if ph and time are not carefully watched. A safer bet would be to use an acid mix sold specifically for yeast washing. Siebels has an acid wash packet with directions which is said to work very well.
In closing I believe that the point here is that even the most basic homebrewer can store yeast in preboiled undistilled water and still achieve success. The yeast can be stored for months and still used. It typically will start faster than a typical Wyeast pack. So relax and have some fun with this idea.
