Please don't get offended. I do not have an agenda, and my goal is simply to brew the best beer possible. These are completely honest questions that I am curious to know the answers to.
First off, ergosterol and UFAs are synthesized during the lag phase by shunting carbon and O
2 to the respirative metabolic pathway. The lower these compounds are when the cells are pitched, the higher the initial O
2 load and the longer the lag phase because these reserves have to be rebuilt. That lag time increase is in addition to the time that it takes the cells to reverse the survival-related morphological changes that they underwent at the end of fermentation. You do not have take my word for it. All you have to do is search for publications that cover the lag phase, O
2 usage, and/or ergosterol and UFA synthesization in Saccharomyces cerevisiae or Saccharomyces pastorianus. You may have to read more than one publication to obtain the core of the knowledge that you seek.
Secondly, it appears that you may have not taken the time to read the entire thread and the entire "Shaken, not stirred lager starter" thread. If you had taken the time to read both threads, you would have known that absolute cell count is not the overall determining factor when pitching propagated yeast. Have you ever smelled a starter that was spun fast enough to create vortex? That smell is not oxidation. It's stress. The geometry of an Erlenmeyer flask prevents O
2 from entering the flask after the culture starts outgassing. Additionally, the reason why a vortex is required is due to the tiny amount of surface area and head space that is available in a 2L Erlenmyer flask that contains 1L of starter wort. A gas (O
2 in this case) dissolves into a liquid at the interface between the gas and the liquid. The vortex increases the media surface area. It also creates a vacuum that pulls air into the flask. How much air the vortex pulls into the flask depends on its strength as well as how open to the flask is to the outside world.
A "Shaken, not stirred" starter is not your typical non-stirred, non-forced O
2 starter. It takes advantage of physics and chemistry to create a massive amount of surface area. A gas-liquid foam has a very high specific surface area. A gas-liquid foam is pockets of gas enclosed by thin layers of liquid. A vortex does not come remotely close to producing the same amount of surface area produced when the shaking procedure is properly executed because there is no way to match it with a gas-liquid two-phase system. Once in gas-liquid foam form, chemistry takes care of the rest based on Henry's law (see
http://www.800mainstreet.com/9/0009-006-henry.html).
One thing that is still not clear is the interaction between the O
2 in the trapped air and the yeast cells that are on the surface of the thin layers of liquid that entrap the air if the culture is pitched before shaking. That arrangement makes available 21 parts per hundred O
2, not 8ppm O
2.
Finally, there are no "cookbook" answers when dealing with yeast cultures. Yeast cells are biological organisms that we can only steer during propagation and fermentation. No two strains behave exactly the same when pitched into a wort (No strain behaves exactly the same way when pitched in two different breweries). If they did, they would produce the same beer given identical worts. Anyone who has ever split a batch between two different strains has experienced different results from the same wort. Some cultures will behave beautifully when pitched at a rate 3 billion cells per liter and produce a lackluster beer when pitched at 10 billion cells per liter. Other strains need higher pitching rates to perform their best. They way that you personally are going to be able to compile the data that you seek is to experiment with the stains in question and take very good notes. You can be assured that professional brewers no exactly how there house yeast will perform when pitched. That knowledge comes from repeated use.
Topic: New starter procedure trial (Read 82674 times)
