Yeast Reuse

Keeping your homebrew cost effective is important. One of the most expensive ingredients in homebrew is the yeast which can run $6 - $8 each. That's a significant cost when added to each batch. The yeast left over after fermentation is just like the yeast you paid $8 for in the tube (or smack pack), so why not reuse it?

Let me clarify something here: yeast cannot be reused indefinitely. Just like any organism, yeast can evolve or mutate over time as more and more generations are created and the characteristics that the yeast impart to the beer can change. Because yeast reproduce so rapidly, the "mutation" of the yeast can take as few as 5 or 6 batches of beer. It also can depend on the yeast strain - certain yeasts are more susceptible to mutation than others. As a general rule, I don't push my yeast past 4 uses, although I've heard of commercial breweries who reuse up to 20 times. You can find you own limitation by experimenting.

My first attempt at reusing yeast was a rousing success. It consisted of racking off beer from the primary fermenter into a secondary, then draining fresh wort directly into the primary fermenter full of yeast. The results were amazing. Activity started within 45 minutes with blow off after only 4 hours. I was impressed. The advantages to this process were obvious: quick ferment starts, no need to make a yeast starter, no need to buy yeast every time, and no cleaning a carboy on brew day. However, the main disadvantage was having to time the brew days such that racking coincided with brewing. That didn't always work out perfectly and sometimes I left beer in the primary longer than I wanted to, just to be able to reuse the yeast. This started to be a problem, so I began siphoning off the yeast into a clean and sanitized jug (my 1 gallon glass yeast starter jugs to be exact) with an air lock attached when my timing of the brewing and racking didn't quite match. I would store the jug in the refrigerator, then just warm it to room temp on brew day and pitch right into the primary.

To make the most of the yeast left in the primary fermenter, you need to understand that for a 5 gallon batch, about 1 cup of yeast slurry is all that is necessary for a healthy pitch rate. There is way more than that in the bottom of the primary usually, so splitting up the primary yeast is a good way to stretch the total amount as far as possible.

My method for this is to get 3 or 4 clean and sanitized 12 oz bottles. Siphon out your wort from the primary into the secondary fermenter and leave behind the primary yeast. Next, mix up the yeast slurry left in the primary really good, then siphon out equal amounts into each bottle. About 1/2 - 2/3 of a bottle is all you will need for a 5 gallon batch. I am usually able to get about 3 bottles worth from the primary. As I explain below, it's not really necessary to get more than that. After each bottle is filled, flush each bottle with CO2 to minimize contact with oxygen, then cap them and put them into the refrigerator.

Typically, I brew 16 - 20 times a year in 5 gallon batches. Since I don't like to push yeast past 4 uses, I can get 3 more uses out of each bottle, but each of those bottles will in turn yield another 3 bottles of yeast. When you do the math, it turns out that you can get 40 bottles of yeast from just 1 yeast tube using this method. That's 3 bottles from each primary ferment for 4 total yeast uses. This is way more yeast than I could possibly use in a year. If you find yourself needing more than that, you could probably split the primary yeast and get 4 bottles per, which would then give you 85 bottles over the course of 4 uses. In any case, it would certainly last any reasonable homebrewer an entire year.

Useful Tips

1. Use an Auto-Siphon. The Auto-Siphon is the best way to siphon wort or yeast. When you are done siphoning out the wort from the primary, remove the debris guard from the inlet end of the Auto-Siphon. Swirl the yeast really well and then put the inlet end of the siphon right down into the yeast slurry. Tilt the carboy so that all of the slurry is gathered in one big pool. Put the discharge tip of the Auto-Siphon into a container of liquid sanitizer. Leave it there and then give the Auto-Siphon a few pumps. It will start to draw up the yeast slurry as you pump. After a couple of strokes, take the tip out of the sanitizer and insert it into one of the sanitized bottles and continue pumping. The yeast slurry is too thick to siphon by itself, so you will have to pump it out manually with the Auto-Siphon. Pump until the bottle is about 1/2 - 2/3 full. Then go to the next bottle, pump some more, etc, etc. The reason you have to submerge the siphon tip at the beginning is so that the Auto-Siphon can prime itself.

2. For one reason or another, the bottles, even when refrigerated, can build up pressure in them over time. Bleed off the pressure in the COLD bottles every week or so by taking a bottle opener and barely lifting up the bottle cap to let pressure escape, then release the cap and let it seal back up. It is especially important to burp the pressure as the bottles are warming to room temperature for a direct pitch or making a starter. If you don't do this, when you finally uncap the bottle, the yeast wants to foam right out. Just remember to burp the cold bottles every week or so.

3. Label your bottles! Put a date, yeast type, and generation number on each bottle. This will help you maintain a first-in-first-out inventory on your yeast. It is also helpful to include the type of beer that was fermented by the yeast in the bottle. I use the small 3/4" white stick on dots on top of the bottle cap and hand write this information.

4. Don't worry too much about going from a dark beer to a light beer with the same yeast. I have successfully brewed an American Wheat with the yeast from a Porter with no problem. However, if you are concerned about it, label each bottle with the type of beer fermented by the yeast in the bottle, then progress from lighter beers to darker beers.

5. Sanitize, sanitize, sanitize.

6. Don't worry about cold break or other products of fermentation getting into the yeast population in the bottle. I've never had any problems with this and I've never had to resort to yeast washing or other procedure. Just pump it straight from the primary into the bottle and be done with it. Personally, I think it's not worth worrying about.

7. Choose your yeast strains carefully. Since my homebrewing horizons are fairly narrow, I typically use two types of yeast for everything. For American beers, I'll use either Wyeast 1056 or White Labs WLP001. For British beers I'll use either Wyeast 1028 (London) or White Labs WLP005. These are great all-around yeasts for the styles I typically brew (see the Recipe Section). From experience, the British yeasts don't store as well as the American yeasts. Don't let them sit for months at a time regardless of the type you use. You need to brew regularly for this recycling process to work well.

8. Make starters for any bottle of yeast that is more than a few days old. The cold temps really put the yeast to sleep and you will do yourself a favor if you go ahead a make a starter, even given the huge population of yeast in your bottle.

9. Taste your starter before you pitch. No, it won't taste like beer, or even taste good for that matter, but you will be able to tell if your starter went Belgian on you. All you are looking for is a clean taste with no off flavors. Just flame the rim of your starter vessel and pour off some of the liquid into a shot glass and taste before you pour anything into your fermenter. This is cheap (free) insurance against ruining a perfectly good batch of wort.