Do you have any sources I can read that support your arguments against stir plates?
Here is a better question; namely, have you ever seen a stir plate mentioned in a published yeast research paper? That is because a stir plate is not the correct device for cell culture. The correct mechanical device is an orbital shaker. That is what White Labs uses in the room where they grow seed cultures for propagation. The use a stir plate in cell culture is an amateur brewer creation that is based on an incomplete understanding of brewing yeast strains. As I mentioned in my blog entry, brewing yeast strains do not need to be stirred to remain in suspension because they belong to the NewFlo phenotype and the claim that they can exceed maximum cell density is nonsense. Brewing yeast strains do not truly respire in wort above the Crabtree threshold, which causes overflow metabolism. What they do is shunt O2 and carbon from the fermentative metabolic pathway to the respirative metabolic pathway for the production of ergosterol and unsaturated fatty acids (UFA) during the lag phase, the spinning the culture continuously adds O2 to the culture is based on not only not understanding how brewing yeast strains operate, it is based on faulty information because very little O2 is entering the flask after CO2 production occurs due to CO2 being heavier than air. About the only beneficial thing spinning does is help to drive off CO2 gas. Other than that, the downsides of a stir plate outweigh the upsides.
As far as to references, I have pieced a lot information together from various publications I have read over the years. I did not cherry pick my information. I continuously check for new research. If you use the search term "brewers yeast respiration Crabtree." you will be rewarded with links to many publications.
Here is one such link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4429655/
The abstract from that publication.
"The capability to ferment sugars into ethanol is a key metabolic trait of yeasts. Crabtree-positive yeasts use fermentation even in the presence of oxygen, where they could, in principle, rely on the respiration pathway. This is surprising because fermentation has a much lower ATP yield than respiration (2 ATP vs. approximately 18 ATP per glucose). While genetic events in the evolution of the Crabtree effect have been identified, the selective advantages provided by this trait remain controversial. In this review we analyse explanations for the emergence of the Crabtree effect from an evolutionary and game-theoretical perspective. We argue that an increased rate of ATP production is likely the most important factor behind the emergence of the Crabtree effect."
Who ever made the claim that stir plates produce more yeast because they continuously aerate the culture knew nothing about how the Crabtree effect.
Isn't intense shaking also going to induce shear stress?
Yes, it will, which I noted in the blog entry. As I mentioned, the starter can be pitched before or after shaking. If one pitches after shaking, it is best to gently shake the culture a second time to disperse the cells.
If you pitch the whole starter, then don't you usually pitch the early flocculating yeast anyway? Isn't pitching early flocculating yeast an issue with yeast cropping/sourcing?
I think that you are misreading into what I wrote or reading into it. Both methods result in early flocculators. The difference is that they are not held in suspension with an SNS starter. The whole argument that a yeast culture needs to be spun to remain in suspension demonstrates a lack of understanding of the NewFlo phenotype (you can Google that one too).
The last I feel often gets confounded, I feel I often read complaints against a particular method in hobbies when the method is independent of the end result. Is the primary issue using a stir plate, or pitching a starter that's fermented out? I typically use a stir plate but start my starter an hour or two before the brew day. When I'm done brewing, the starter is usually at high krausen and I pitch the whole thing.
It is primarily an issue of stir plates being promoted as the best way to make starters to new brewers, which is not based on peer-reviewed science. It is based on amateur brewer dogma just a like the dogma of using a secondary fermentation vessel to avoid autolysis. Luckily, the use of secondary fermentation vessels has died off. My goal is to educate new and exiting brewers about the fallacy of promoting stir plates as the best way to make a starter because it is not backed up by science. The absolute best way to make a starter is to saturate the starter wort with an O2 bottle and a diffusion stone before the culture is pitched (pure O2 provides for a higher saturation level than air). However, that method imposes cost and the responsibility of keeping a diffusion stone sanitary. As mentioned in the blog entry, my method of making a starter is not do all, be all method for making a starter. What it is is simple, low cost, and highly effective. The proof is in the pudding that few of the people who have tried SNS after using a stir plate went back to using a stir plate. Why would a brewer work harder than he/she needed to in order to achieve a comparable result?
By the way, I am not targeting you. I expect to get heavy blow back from the blog entry. People do not like to feel like they have been taken for a ride based on faulty information.
A few more posts since I last checked this out...
I think people should use whatever method works for them. I've done SNS and used a stirplate, and I tend to use my stirplate. I've got a newborn, so once it's started I don't have to swirl or do anything to release CO2 from solution. I think there's also a huge number of homebrewers who've successfully used a stirplate without creating a "foul smelling thing."
TLDR Version:
- It truly doesn't matter how you manage your starter as long as you provide enough oxygen and remove CO2 periodically.
- CO2 toxicity is real, and swirling by hand or stirring gently with a stir plate will increase growth
- CO2 blanket doesn't apply when there is fluid (gas) movement.
- A stir plate can absolutely add O2 to wort, until there's sufficient yeast activity/CO2 output from the wort that positive pressure is created in the vessel which limits O2 ingress (Airlock activity/lag is typically 4+ hours, high krausen in 12-18)
- Flavor profiles of yeast are relatively consistent through a range of pitch rates (strain dependent), so if your starter is off "optimal" by a few M/ml it's going to be fine.
- "If you're using a stir plate, shaking, or aeration, the yield will be higher" Yeast J. Zainasheff & Chris White
I'd also say it's unfair to say no testing or research has been done regarding starters at a homebrew level. Take a look at "Yeast" by Chris White & Jamil Zainasheff. Your claims of "foul smelling things" also fly against the experience of many homebrewers, who use stir plates without issues.
Carbon dioxide toxicity is something that is confirmed by science. This is commonly tested in a bioreactor, with oxygen continuously supplied. With this optimal setup, yeast growth and health is slightly inhibited when CO2 becomes greater than 40% of the solution, and significantly inhibited at concentrations above 50%. From data collected by Die_Beerery, you can see that yeast will consume 10 ppm of dissolved oxygen in an hour. It thus seems self evident that without regular agitation, yeast growth will be limited.
https://www.themodernbrewhouse.com/wort-study-1/https://pubmed.ncbi.nlm.nih.gov/786407/Our tests showed that vigorously shaking a starter every hour results in approximately double the number of cells created when using a starter that is not shaken.
Yeast Whit & Zainasheff
The yeast will do best when the starter setup continuously releases the carbon dioxide they reate, keeps them in suspension and evenly distributed throughout the solution, and provides them with access to reasonable amounts of oxygen.
Yeast White & Zainasheff
Carbon dioxide is heavier than air, but that's not relevant when there's moving fluid. It might factor in an environment like a cave where there's no air movement, but actively fermenting yeast puts out CO2. This would only limit oxygen intake if you have an airlock in place, or the positive pressure of carbon dioxide put off by the starter exceeds the atmostpheric pressure. High krausen is typically achieved in 12-18 hours (White & Zainasheff), and many beers see airlock activity in 4+ hours so I think it's safe to say that a starter will take up O2 from the atmosphere for a few hours after yeast is pitched.
Hopefully this was rambling and incoherent enough, I had to piece it together in between a dozen or so diaper changes.
Topic: Shaken, not Stirred: The Stir Plate Myth Buster (Read 14611 times)
