Hey guys, I’m brewing a pilsner this weekend and I’m using my harvested yeast that i collected from my munich helles. I cleaned it very well and its really young (collected this week). I have 3 mason jars and about 30ml each of very white compacted yeast. Considering 4mil cells/ ml thats only 360 mil cells. By the calculations, i need almost 1 trillion cells and 2 stage 3 liter starters (15 gallons, 1.048 og). That seemed way too much to me. Anyone who has experience repitching lager yeast can help me? Are my estimations correct? I have time until brewing so doing 2 starters wouldnt be that bad but i just wanna make sure i need that much yeast
Please tell me that you did not rinse your yeast with boiled water. Yeast rinsing is an unnecessary rookie move that adds no value while placing the culture at risk of infection due to removing the protective environment the culture built for itself.
With that said, you are probably looking at an 11 to 12 degree Plato beer. At 1m cells per degree Plato, you need around 12 * 1,000,000 * 57000 = 684 billion cells to the get the job done with good sanitation coupled with solid aeration. Using unwashed thick slurry, you are conservatively looking at 1.2 billion cells per ml, 684 / 1.2 = 570ml of thick slurry. You can actually get away with as little as 750,000 cells per ml per degree Plato (if you have the stomach for it and are extremely anal when it comes to sanitation, you can get away with less than 750K, way less). I just pitched a package of Imperial L28 straight into 20L of well-aerated 14P wort without making a starter. My fermentation temperature was set to 54F/12C, which is middle of the range for that culture. Active fermentation started in less than 24 hours, which is respectable for an initial lager pitch. Imperial states that their packages contain 200B viable cells when shipped; therefore, I was looking at a best case scenario of 200,000,000,000 / 21000 = ~9.5m cells per ml. That pitching rate yields a per ml per degree Plato pitching rate 9.5m / 14 = 680K cells. While the package was relatively new, I would estimate that I could count on there being 500K cells per ml per degree Plato. That is even lower than George Fix’s pitching rate of 750K cells per ml per degree Plato. In reality, yeast cultures are like nuclear weapons in that one only needs to be close to one’s target to get the job done. The difference between 9.5m cells per ml and 19m cells per ml is one replication period. Replication requires O2, so wort aeration is much more important than precisely hitting one’s cell count target.
You can get away with rinsing yeast with boiled and cooled water, I used to as well, but it does increase the chance for an infection. The yeast maintain a lower pH as a protective measure against bacteria, which do not thrive at beer pH levels. When replacing the beer with water you raise the pH toward 7, and increase this risk.
Now what are the benefits of washing yeast? I used to because John Palmer’s book, How To Brew, told me I “needed” to separate out the trub. This seems logical because washed yeast lacks the large amount of trub and looks prettier than unwashed. However, I have found no negative effects of a little trub that gets through when I decant while pitching.
Basically, it has always been a bad move that has been difficult to kill because every newbie wants to gain some street cred by publishing an article on yeast rinsing. Do you want to know where the practice of rinsing yeast with boiled water originated within the amateur brewing community? Charlie Papazian introduced it in the “New Complete Joy of Homebrewing” (it may even date back to an earlier publication of that book). He also promoted the use of a secondary fermentation vessel as a way to prevent autolysis. While using a secondary fermentation vessel to prevent autolysis has gone the way of the do-do bird, amateur brewers still cling to yeast rinsing, a practice that is not based on science and provides no microbiological advantage.
Brewing yeast strains are Crabtree postiive. What that means is that whenever the medium gravity is above the Crabtree threshold of 0.2% w/v (an S.G. of 1.0008), brewing yeast cultures will chose fermentation over respiration even in the prescence of O2. There is scientific evidence that brewing cultures became Crabtree positive due to competitive pressure. You see, the main reason why we have cell counts in the first place is that they are primarily a safeguard against a micro-oganism other than the pitched yeast culture owning the wort. From the time a yeast culture is pitched until the culture grows large enough to reach high krausen, it is in competition for ownership of the wort with wild microflora (boiled wort is not absolutely sterile and sanitization is not a synonym for sterilization). A yeast culture owns a batch of wort by doing three things. First, it consumes all of the dissolved O2, shutting out aerobic microflora. It then lowers the pH to around 4, which shuts out pH sensitive microflora. The pH sensitive microflora include the pathogen Clostridium botulinum, which cannot replicate below a pH of 4.6. The final defense that a yeast culture mounts is the production of ethanol, which is toxic to all living organisms at a given level, even human beings (i.e., people die from alcohol poisoning every day).
When a brewer rinses yeast with boiled water, he/she removes the protective force field that a yeast culture built for itself, basically opening it up to infection from house microflora while providing zero microbiological advantage. A yeast culture does not need to be kept free from trub and hop particulate matter. It needs to be kept as free from wild microflora as possible because every time a culture is pitched, it presents an opportunity for microflora other than the culture to replicate. This reality is what places an upper limit on bottom-cropped yeast more so that any other other reason when a yeast culture is not serially overpitched.
Now, top-cropping is an interesting take on cropping. While top-cropped yeast should also be stored under green beer, top-cropping naturally purifies a yeast culture because wild microflora do not floc to the top, which means that top-cropped yeast can be re-pitched almost indefinitely as long as care is taken to not infect the culture. The sad thing is that I have never heard of true top-cropping lager yeast.
If you need further evidence that yeast rinsing is an amateur brewer fabrication that is not based on microbiology, watch how a craft or industrial brewery bottom crops yeast. They either pump it out of the cone into a yeast brink for temporary storage or into a fermentation vessel with fresh wort. I have yet to see a professional brewery rinse yeast with water before repitching it.
I don’t know the science, but I’ve cold stored yeast in clean sanitized Teddie peanut butter jars (under the beer it made) for weeks and used it to make other batches. I let it warm up and proof it like you would with bread yeast before pitching just to make sure it’s still alive.
yup, frankly i didn’t hear about yeast “washing” until well after the fact that i was simply reusing yeast from a finished beer, which is so natural a brewing thought/action that it has been going on for thousands of years.