Washing vs Rinsing
Yeast washing involves acid & killing other microorganisms in the yeast sample. If you are harvesting your yeast to save money, don't bother. At the homebrew level it is very inefficient; you will save considerable money & time by just buying a new pitch. If you enjoy learning & working with yeast, it's a very challenging technique to master but can be a fun path to experiment with. I wouldn't recommend it to anyone beyond it's educational value.
Yeast rinsing is a much simpler process & is a great tool for homebrewing great beer as well as saving money. It is simply seperating the best yeast in a sample from the over/under flocculant yeast & non-yeast, such as trub, hop matter & precipitated proteins.
A Note on Sanitization:
Sanitation is key to the process. Every single thing in every single step gets sanitized or sterilized. Nothing gets left in the open any longer than it absolutely has to. Sanitize your entire work area as well. Don't rinse yeast the day you vacuumed or even the day after (especially if you have pets). Turn off all fans, you want the air as still as possible. I live alone, so it's never a problem but if you have kids running around or a spouse trying to get something done, find a quiet corner or a better time to do it. The cleaner you are, the better results you'll get.
The Idea:
Yeast both flocculates & settles. Often these are confused or thought of as the same thing. Flocculation is the yeast grouping together & forming larger particles. This helps them to settle out, but isn't the action of settling out. If we swirl up yeast in a jar & watch it settle, the first things that are falling out are trub & hop matter, mixed in with the overly flocculant yeast. Gradually less and less flocculant yeast settle on top finishing with precipitated proteins. Obviously we are looking to pitch yeast, so all the non yeast has to go & not all that yeast is the same. The over flocculant yeast, near the bottom, isn't going to attenuate the beer very well since it's dropping out of solution too soon. The under flocculant yeast, near the top, will stay in solution too long creating a number of problems in the final product such as clarity, aroma & flavor. Yeast rinsing is the method we use to get that 'just right' yeast & disposing of all the rest.
The Equipment:
- yeast sample
canning-type pot
metal tongs
sterilized, deoxygenated water
sterile jars
aluminum foil
The Preparation:
After you harvest your yeast sample, crash it in the fridge for 24 hours to 3 days. You want it nicely settled in the bottom of your harvesting vessel.
I prepare the water & jars at the same time. Start by lining the bottom of a large canning-style pot with mason jars (no lids). Fill the pot with water to 1-2" above the jars. I also put my tongs in there vertically so just the end is sticking out. I use the generic all metal kind you can get from any restaurant supply store - they sterilize in the boil well, don't have many parts & no soft surfaces that could potentially hide a contaminant - just don't be rough with the jars. While you bring the pot to a boil, prepare a piece of foil for each jar. Too big is better than too small. You want to be able to cover all the threads on the jar tightly. You can sterilize these foil squares with the boil or steam, but I've had no problems Just using StarSan. I hold a hard boil for 8-10 minutes before removing the first jar & let it continue until the last jar is out - the escaping steam is somewhat of a protective barrier. To remove a jar use the tongs to gently pull it halfway out of the water, pour out a small amount (~10% of the jar's volume). Quickly but carefully remove it the rest of the way & place it on the counter. Cap it with the foil as quickly as possible. Repeat for the rest of the jars. Let them cool at room temperature until they can be safely handled with bare hands before transfering them to the fridge. I generally do about a dozen at a time & use them over the course of several weeks.
The Rinsing:
Remove your settled yeast sample & a jar or two of water from the fridge & allow it to naturally warm up. I've had good results rinsing around 55F, but I don't watch it down to the degree. A bit below room temp is fine. Remember to keep a spray bottle of StarSan handy as you'll want to re-sanitize frequently. Anytime removing the foil from one of the water jars, cap it as quickly as possible - even empty ones as you may need them for transfers (you don't have to use the sterilzed jars for each transfer but it is the best option - that being said, I have used well-sanitized growlers frequently with good success & always flame the opening prior to a transfer).
First decant the majority of the liquid off the yeast sample. You want just enough left to swirl it into a fairly thick but pourable slurry. If the yeast vessel has anything stuck to the inside walls like a foam line from a starter, transfer the slurry to a water jar, otherwise you can use the same vessel. Dump the water from one if you need to. Add water & swirl to thin it out evenly. It can vary depending on how thick your slurry started at, but roughly the same volume of water as the slurry. You can alter how the yeast settles with the thickness of the thinned out slurry. Leave it still for a few minutes to allow the over flocculant yeast & any heavy non-yeast to settle. Transfer the liquid to another vessel, leaving the bottom layer behind. Allow it to settle for several more minutes & decant the majority of the top liquid containing the under flocculant yeast & protein matter. Place your rinsed yeast sample in the fridge it will settle out further leaving a somewhat protective layer of deoxygenated water on top.
Using Your Rinsed Yeast:
The rinsing process is stressful to your yeast. Not as much as temperature shock from pitching too hot or cold, but it's still certainly not the best for them in terms of cellular health. You harvested them post-fermentation, so they're already pooped out & then you chill them down into near dormancy. It's really taken a toll on their reserves. Always do a starter when using rinsed yeast. In my particular method, I harvest, rinse, build cell count to an appropriate pitch & rinse again. If you're in the same boat & already have an appropriate cell count, do a small starter & pitch at high krausen. If you still need more cells, then let it finish out. The starter is no different than working with a vial or smack-pack.
The Not-So-Fine Print:
This is a skill that develops with practice & a watchful eye. There are no cut & dry answers unless you're analyzing each step, doing cell counts, densities & such. Your first time trying it, don't remove too much. While you want to keep the number of transfers to a minimum, you can always rinse a sample again if you need to but you can't get the stuff back that you already dumped. The more samples you rinse, you'll start to get a good feel for your amounts & timing. Each strain of yeast behaves quite differently, so you will have to alter those amounts & timing depending on what you're working with. I would suggest learning & dialing in the process with your favorite strain before experimenting with others. If you already know how your 'house' strain ferments, you can pick up minor problems in the ferment that you missed while rinsing or doing your starter & fix your process accordingly.
BN Army // 13th Mountain Division 
