I am both Yeast Whisper and S. Cerevisiae. They are my old user names on two different sites. Denny and those who are in the know can attest to the fact that I changed my user name on this site in 2016 (I have a blog on Denny and Drew's site under which I blogged as Saccharomyces). I did so because my ex-wife reported a neighbor to county zoning who was illegally using his residential property as a commercial high-performance automotive service shop, complete with a dynamometer that was unbelievably loud when in use. His customers also used to burn-out in front our home when leaving his illegal shop (the road looked like a drag strip). When he lost his battle with zoning, my neighbor decided to attempt to make our lives miserable. Not only did he damage property we owned, he cyber stalked us and attempted to ruin our reputations. He reported that I was posting to this forum on company time after he made the connection between my real name and my user name on the site. As much as I hated it, I accepted that consequence because I was doing something wrong that needed to be corrected (which is why I no longer post during the day during the work week). However, the straw that broke the camel’s back was when he started to cause trouble on this forum and harass AHA headquarters. That is when I decided to close my S. cerevisiae account and create my Saccharomyces account. People I know from the site who I met at NHC have kept my real identity undisclosed because they know the back story, which is something that I appreciate.
With that said, not wanting to pour media into a glass container is a non sequitur. I switched to using a 5L borosilicate glass (Pyrex and Kimax are common brand names for borosilicate glass) media bottle years ago, so that I did not have to wait until the starter medium cooled (I believe that there are photos of my old Corning 5L media bottle on this site as well as the site on which I posted as Yeast Whisper). Large media bottles are not cheap new from a labware supply company, but they can be had new for 50% of what they cost from a labware supplier on eBay if one is patient and even less if one is willing to go second hand. Starter media can be poured into a borosillicate glass media bottle or any other borosilicate glass labware hot, which means that all the media bottle and GL45 cap need to be is clean. The starter medium will sanitize the media bottle and the loosely attached GL45 cap if allowed to stand for around 30 minutes before cooling because the starter medium will bring the bottle and cap up to at least the Pasteurization temperature of 145F (the time period is reduced to 15 seconds if the bottle and cap reach 161F). That is a heck of a lot safer than boiling in an Erlenmeyer flask, as is practiced by many homebrewers. Due to their design, Erlenmeyer flasks are not designed to be used for boiling, which is why they tend to break when put on a heat source. The proper piece of glass labware to use for boiling is a boiling flask, which is round to evenly disperse the stress that occurs when heated.
An orbital shaker is a very different device than a stir plate. The flasks that are normally used on orbital shakers may resemble an Erlenmeyer flask, but there are significant differences. Shaker flasks have baffles on the bottom. They also tend to be wider and shorter. The wider body is to increase the surface area for oxygen diffusion. The baffles exist to increase turbulence, which causes the media to foam. What most homebrewers do not know is that yeast cultures do not use oxygen in the average starter after the they have entered the log phase where exponential growth occurs due to the fact that the medium is above the Crabtree threshold. The keeping the yeast in suspension using a stir bar argument also demonstrates a complete lack of understanding of how yeast cells behave. Viable yeast cells naturally stay in suspension until they have exhausted all of the sugars that they can metabolize; therefore, there is no need to stir. All stirring does is keep non-viable cells in suspension. Shaking the medium into foam provides significantly more dissolved O2 than a stir plate does the entire time it is spinning the bar. The stir bar also places shear stress on the cells, which is why the starter medium from a stirred culture smells foul. Even if one allows a Shaken, not Stirred (SNS) culture to ferment out and enter quiescence, it never smells foul unless the starter has been contaminated. An SNS starter is also significantly easier to make and much cheaper if a repurposed 1-gallon apple juice jug is used (the caveat is that the temperature differential between the jug and the starter medium cannot be large).
The reason why one pitches at high krausen is because it signals the shift from exponential growth to the stationary phase. What that means to a brewer is that he/she has obtained maximum cell density without allowing the yeast cells to unnecessarily expend unsaturated fatty acids (UFAs) and ergosterol reserves, which means that less oxygen and time are necessary for the lag phase after the culture has been pitched. The UFAs and ergosterol that the mother cells store during the lag phase are shared with all of their daugther cells. The cells that are produced after the exponential phase has completed are for replacement only; therefore, they unnecessarily deplete UFAs and ergosterol. If one allows the cells to enter quiesence, one has to deal with cells that have undergone morphological changes in order to survive lack of carbon to metabolize for energy. Sugars are carbohydrates. Carbohydrates are composed of carbon bound to water (read my article entitled “Carbon Credits,”
https://www.experimentalbrew.com/blogs/saccharomyces/carbon-credits).
What we need to remember is that knowledge is power and myth is just that, myth. One can either except myth or one can seek to understand what is actually happening during cell culture. However, to say that using a stir plate produces a better culture is just mythological nonsense. A stir plate is better than just pitching a culture into a starter medium without any attempt to oxygenate the medium in some way, but that is a pretty low bar. The time to add oxygen to a culturing medium is before the culture is pitched or right after it has been pitched. If one gets that right, the rest is easy. The specific surface area provided to a culture in an Erlenmeyer flask is not large enough to cause significant oxygen diffusion. Sure, stirring the culture fast enough to create a vortex improves the situation by increasing the specific surface area and exposing more of the medium to the slightly larger specific surface area by turning it over, but it comes at higher sheer stress. Here’s an experiment to try. Make two starters and place them on stirplates for 24 hours. The first culture is spun fast enough to create a significant vortex. The second culture is spun very slowly. Now, smell each culture after 24 hours have elapsed. More often than not, the culture that was spun fast enough to create a significant vortex will smell much worse than the culture than was spun slowly. That is the smell of shear stress. Shear stress negatively impacts the health of the yeast cells.
In then end, if one wants to use a piece of mechanical lab equipment to make starters, one should stick to using an orbital shaker and shaker flasks. That is what White Labs uses when starting new yeast cultures from working cultures in their bank (The orbital shaker used in the propagation lab is an amazing thing to see because it is multi-level). White Labs stores its long-term cultures in a liquid nitrogen-fueled freezer that is capable of reaching -196C.
Here is a link from probrewer.com where the author covers propagating yeast directly from a single-cell isolation plate (each distinct round colony is the offspring of a single yeast cell):
https://discussions.probrewer.com/forum/probrewer-message-board/brewery-operations/yeast-q-a-sponsored-by-lallemand/34576-laboratory-propegation-and-brewery-propegation-of-yeast-sops Usually, one or more colonies are aseptically transferred to an agar slant for storage and the first-level starter is innculated from slant, not directly from a plate (however, starting from a single colony ensures that the culture grown is a single-cell pure culture). I will often transfer more than one colony to slant or create several slants from individual colonies if I suspect that a yeast culture is multi-strain. That is what I did when I cultured from a hydrometer sample I collected at a Ringwood brewery back in 1993.
Topic: A question on the "shaken-not-stirred" starter... (Read 5017 times)
