I read somewhere that reusing dry yeast was not recommended, but wanted to see if others had any experience with reusing 34/70. I have a 5 gal batch of pilsner fermented with 34/70 that I would like to repitch into a larger 10gal batch of Oktoberfest. I was planning to pitch half of the yeast cake into each 5 gallon batch of the Oktoberfest. I am using 2 buckets for the 10 gal batch. Any issues with doing this?
Never had a problem reusing any dry yeast.
I read on one of the dry yeast mfrs sites that they recommend it not be reused.
Here it is: http://www.fermentis.com/brewing/homebrewing/frequently-asked-questions/
Can I re-use the yeast?
Due to the risks of infection and the inability to check yeast cell counts of yeast slurries it is not recommended as the risk of failure is increased and outweighs the cost of new yeast.
Edit: But the Danstar tech data sheet for London ESB says “When using Lallemand Brewing Yeasts, you may repitch the yeast just as you would any other type of yeast according to your brewery’s SOP for yeast handling.” LOL
which are exactly the same concerns with reusing any yeast, liquid or dry. Dry yeast is not more prone to those issues than liquid, yet we reuse liquid yeast all the time.
Wasn’t it, once upon a time, that dry cultures weren’t pure cultures (something to do with the drying method) and so they weren’t suitable for use over many propagations? I don’t imagine this is the case anymore, but I’m wondering if this is some bit of knowledge that has lasted beyond its relevancy.
I even read lager yeast shouldn’t be reused because it absorbs DMS in the fermentation D rest so when reused could increase the chance of DMS in the new brew. If it’s on the internet it has to be true right? (I read ‘6 myths’ on AHA by Denny last night.)
well, I don’t do a d rest, so I guess I’m OK! 
Hey that’s why this forum is needed. We can learn and change our misconceptions :) Thanks for your advice!
I generally keep a pack or 2 of US-05 in my yeast fridge just in case. I recently found myself with only that for ale yeast and one packet was dated. Didn’t have any reason to use it for quite some time. The second packet was getting close to 2 years old, so I rehydrated it and then pitched it into a starter to produce a couple of 100B cell vials. I used these vials as I would fresh liquid yeast and they performed well. While I use mostly English ale yeasts for my APAs and IPAs, I haven’t found a dry English ale yeast that I prefer over the liquid offerings.
Not sure if first rehydrating is necessary when making a starter from dry yeast, but I prefer to err on the side of caution. IMHO, today’s dry yeasts are of a quality comparable to liquids. As for re-use, US-05 is reputed to perform much better when re-using than on the first pitch.
I have started using 34/70 for my lagers this summer and have saved the yeast and it is going on it’s 4th batch. I don’t see any negatives to saving it and reusing. In fact I think the fermentation has gotten stronger as the generations move forward. The first batch fermented well but the second and third batches had shorter lag times, and seemed to ferment well. The beers tasted amazing too. I only plan to use a couple more times before I start over with some new packs though.
I just pitched an 8th generation slurry from two packs of 34/70 that I re-hydrated at the beginning of the year. I’ll probably go two more and start over.
I’ve repitched slurry from both US-05 and 34/70 with no problems.
Fermentis’s position is one part an unspecific statement of fact (repitching yeast always invites risk of infection) and one part straight marketing (it’s cheaper to buy new yeast). Put them together it’s just advising you to buy more of their product.
Of course the manufacturer says don’t repitch. I’ve actually found 34/70 works better when repitching. I’ll start my lager series in November and keep repitching until March. I’ve done this for 3 seasons and haven’t noticed any difference pitch to pitch
Man, I’m always amazed at how this forum supports my brewing. Right now I’m cold-crashing an O-fest, with plans to repitch the 34/70 into a Munich Dunkel tomorrow. I think that as long as the initial fermentation was clean and healthy, the slurry should be in better shape than the original dry pack. Maybe I’m vastly oversimplifying things here.
One thing that I recently picked up here was the idea of overbuilding starters in order to maintain a cleaner yeast culture. I’ve been using that method a lot in my brewing, and I like it a lot. So, the downside with repitching is the gamble of contamination. I plan to reserve a clean portion of my yeast slurry from the Ofest as my “pure” culture, and then build that through starters for future lagers.
However, a whole batch worth of lager slurry is way to valuable to just dump, so I see myself overbuilding a starter, brewing a batch, then using the slurry for a second batch or two. I don’t brew lagers that often, but I’m definitely going to keep moving forward with this method as a way to simplify lager production.
PS - doesn’t dry yeast pretty much turn to liquid once you use it?
I have gone to using dry yeast in the summer months and not repitching during the summer due to a concern that there is just a higher degree of airborne contaminants during the warm months, so any collection and repitching is more perilous in the summer. Probably overkill, though, because if you pitch enough yeast it should outcompete a minor infection, right? I just try to minimize the chances of an infection. Also I have found that I really like S-189, so it is pretty easy peasy to use that for my lagers without needing to repitch.
I know this is an old thread, however it almost had all the information I required. When harvesting 34/70 and then when it is time to pitch, does one use half or the entire amount of the harvested yeast. I know ale yeast it is about half, just not sure about lager yeast.
That depends on what you are making. 34/70 is a lager yeast so I will comment on using it for a lager recipe. Use all of it, making sure you have the proper pitch rate. I personally don’t worry about that when repitching. Pour most of the beer off, swirl the remaining and pitch. I have gone, if I remember correctly, 6-7 generations with 34/70 without any perceptual difference. I also will pitch straight from the cooler. No need to let it warm up.
You want to pitch around 150ml of settled, thick slurry per five gallons of wort, especially if you plan to serially repitch a culture. Underpitching is okay. Overpitching leads to insufficient new cell growth to sustain a culture over multiple repitches.
I find the yeast picthing calculators handy and convenient. Gives you an idea how much yeast you need for every batch. Mrmalty.com
I have counted counted cells with a microscope and hemocytometer and matched it very closely with these results.
I have also counted stained yeast cells using an hemocytometer and a microscope. It is an interesting exercise and necessary for commercial brewing, but has limited use at home. At this point, I really do not find yeast calculators to be all that useful. I find rules of thumb combined with my experience with a culture to be more useful. That being said, what is interesting is that Mr. Malty’s standard re-pitch suggestion is 173ml, which is basically a 1L starter at maximum cell density. His ale pitching rate is 500ml at maximum cell density, which solidifies my assertion that underpitching by as much as 50% makes no difference in fermentation outcome while providing enough new cell growth that a culture can be serially re-pitched more than a couple of times without worrying about a huge loss in viability, that is, as long as one’s wort is well aerated. I have always re-pitched between 150 and 175ml of settled slurry per 5.25 gallons. That is based in the rule of thumb that 1ml of settled, thick slurry contains approximately 1.2 billion cells as well as the accepted average maximum cell density of a 1L starter, which is 200 billion cells. If we divide 200 / 1.2, we get 167ml; therefore, pitching anywhere between 150 and 175ml of settled, thick slurry will yield approximately an equal number of cells as a 1L starter at high krausen. Pitching less less slurry will yield more new cell growth in well-aerated wort while pitching more slurry will increase the average age of the cells in the culture due to suppressed new cell growth. That is why overpitching is a poor practice in a serially re-pitched brewery. It is better to improve brewery hygiene than overpitch to avoid contamination from wild microflora. For most part, we do not base pitch rates based a fermentation reaching projected terminal gravity. That is function of genetics and dissolved O2 demand. We can seriously underpitch if there is enough dissolved O2 to support the number of replication cycles necessary to reach maximum cell density and our brewery hygiene is impeccable. Suggested pitching rates are for commercial brewing, which accounts for the difficulty encountered in keeping a commercial brewery and brewing equipment spotless. Pitching rates are primarily about outcompeting competitors.