I happened to save this post from another forum by YeastWhisperer / S. cerevisiae, the person that, I believe, takes the credit for the SNS terminology and introducing it to the homebrewing community. I think it helps explain the main benefits of stirred vs. "shaken once until very foamy" starter approach.
https://www.jimsbeerkit.co.uk/forum/viewtopic.php?f=12&t=70926&start=30"Gas is absorbed at the interface between a gas and a liquid; therefore, gas permeability is bounded by specific surface area. One liter of medium that is shaken until it is almost foam has a huge amount of amount specific surface compared an equal amount of medium in pure liquid form. A non-direct O2-infused, stirred 1L starter does not begin to approach providing the same level of dissolved O2 to a culture at the beginning of incubation as does a well-shaken starter. In fact, a non-direct O2-infused stirred starter does not come close to providing the same amount of dissolved O2 over the entire period that a culture is stirred because most stirred starters are made in conical flasks. The surface area of the gas-liquid interface is reduced as the volume of liquid is increased in a conical shaped vessel. Almost no O2 exchange occurs after the culture starts to outgas due to the fact that the culture is under positive pressure and that CO2 is heavier than air. The cells in a stirred culture also have to deal with continuous shear stress. I am not pulling the shear stress problem out of thin air. It is a well documented and researched problem that plagues designers of bioreactors, and bioreactors stir at very slow rates while injecting O2 (perform a Google search on the terms "bioreactors" and "shear stress"). New patents are applied for in this area on a regular basis.
I can go grow a pitchable culture from a 4mm loop of yeast cells in as little as 2 days using my method. Most home brewers are pitching a culture that contained 100 billion cells at the time of packing. A four month old culture that has not been abused contains approximately 1/4th of the number of viable cells that it contained when packaged; therefore, a four-month-old White Labs vial contains approximately 25 billion viable cells, which means that we are looking at log(200 / 25 ) / log(2) = 3 replication periods to reach maximum cell density if pitched into one liter of medium or 4 replication periods if pitched into two liters of medium. If the culture is held at at least 21C, a replication period should be approximately 90 minutes; hence, we are looking at a worse case scenario of 6 hours beyond the amount of time that it takes the cells to exit the lag phase.
Anyone who is making a one or two liter starter from a commercial yeast culture several days in an advance is pitching quiescent yeast cells. Quiescent yeast cells take longer to exit the lag phase because they have to reverse the morphological changes that they underwent in preparation for quiescence. Quiescent cells also place a higher O2 load on the batch of wort into which they are pitched because they have low ergosterol and unsaturated fatty acid reserves."
Topic: A question on the "shaken-not-stirred" starter... (Read 5046 times)
