See page 7 of this thread https://www.homebrewersassociation.org/forum/index.php?topic=21705.msg276016#msg276016
The takeaway is that Mark sees stressed, continually aerated wort as a bad thing and that a healthy pitch of the entire starter which was aerated thoroughly at the beginning and pitched at high kreusen is better.
Actually, that's an incorrect takeaway. A stir plate provides inadequate aeration if operated at a speed low enough to prevent shear stress (perform a Google search using the terms "magnetic stirrer" and "shear stress"), and if operated at a speed high enough to add significant O
2 to a culture results in shear stress being placed on the cells, which is why cultures that are stirred fast enough to create a vortex smell foul. Physics prevents a culture in an Erlenmeyer flask from receiving O
2 after it starts outgassing because gas pressure is highest at the mouth of the flask.
With that said, stir plates and orbital shakers are completely unnecessary in a home brewery (I purchased my orbital shaker for experimental reasons). A better investment is an O
2 diffusion stone and a source of O
2. Brewing yeast cells will grow to fit their environment if given enough O
2 and carbon (sugar is carbon bound to water; hence, the term carbohydrate). Most brewing yeast cultures do not need to be stirred because viable cells naturally remain in suspension due to something known as NewFlo flocculation. NewFlo strains do not aggregate until glucose, mannose, maltose, sucrose, and maltotriose have reached genetically set levels; hence, most brewing cultures do not need to be stirred to keep the cells in suspension.
As I have mentioned many times before, my method is a low cost, low-tech way to produce a healthy yeast culture. I did not set out to create a low cost, low-tech method for making healthy starters. It was a case of serendipity. I was preparing starters using English measurements at that point in time. I made one quart starters in a 48oz glass Ocean Spray Cranberry juice bottle. I went to make a starter and noticed that the bottle was cracked, so I decided to use a 1-gallon glass jug that I used to make mead for my starter. Shaking until the culture was almost completely foam was the result of being strong at that point in my time due to spending my teenage and my twentysomething years in the gym. I used the method for several years before it dawned on me why starters made in the 1-gallon jug worked better than those made in a 48oz container. The reason is foam. It is easier to make 1 quart of wort expand into foam in a 1 gallon container than it is in a 48oz container, and wort in gas-liquid foam form has a much higher specific area surface than wort in liquid form, which leads to increased O
2 pickup. In essence, my method is a poor man's O
2 injection system.
Topic: Stir Plates (Read 4895 times)
