To which of course I was told that I basically had no frame of reference and that I needed to read all the science behind it and read "Yeast" and if all the breweries in the world are doing it why was I ignorant of the fact that better beer can't be made without Pure O2......
Next time one of those one-year-wonder brewers goes off on a tangent about how one cannot brew good beer without using pure O
2, ask him (it will be a him because women do not suffer from too much testosterone syndrome) what O
2 is used for in a fermentation and if there is anything that a brewer can do to limit the O
2 load in a fermentation. You can then sit back with a bag of popcorn as he scrambles to come up with a coherent answer.
Yeast use O
2 to synthesize ergosterol and unsaturated fatty acids (UFA). They do so by shunting O
2 and a small amount of carbon (sugar is carbon bound to water) to the respirative (aerobic) metabolic pathway (all reproduction in wort is fermentative due to the fact that brewing yeast strains are Crabtree positive). Ergosterol and UFAs make the plasma cell membrane more pliable, which, in turn, allows nutrients to enter and waste products to exit the cell.
One of the reasons why aeration is such a hot topic today is because more and more home brewers are pitching quiescent yeast cells (thanks in large part to disinformation being spread on HBT). Twenty years ago, the average home brewer who made a starter knowingly or unknowingly pitched at high krausen. The drill was to smack a pack of Wyeast (White Labs was a non-entity for the most part) the morning before brew day, allow it to swell during the day, make starter in the evening, and pitch the starter the next day. Today, people are making starters days in advance and allowing them to ferment to completion, so that they can decant the supernatant. By doing so, they are increasing the initial O
2 load placed on the wort when the culture is pitched.
All allowing a starter to ferment past high krausen does is waste ergosterol and UFA reserves because the mother cells that were in suspension while O
2 was still in solution share the ergosterol and UFA reserves that they built with their daughter cells. High krausen occurs as the culture reaches maximum cell density. All replication beyond this point is for replacement only, which means that we are wasting ergosterol and UFAs when we allow a starter to ferment out.
High gravity and high alcohol beers share one thing in common; namely, the environment is hard on yeast cells, which means that cell membrane health is even more critical in high gravity/high alcohol environments. What makes cell membranes healthy? Ergosterol and UFAs make cell membranes healthy. The reason why high gravity and high alcohol solutions are hard on yeast cells is because both environments draw water out of the cells. In the case of high gravity wort, a phenomenon known as osmotic pressure is responsible for drawing water out of the cells. Osmotic pressure is the result of the solute levels being different on opposite sides of a semi-permeable membrane. Water is drawn to the side with the higher solute content (the hypertonic side), which is the wort. In the case of high alcohol, alcohol is hygroscopic. Anyone who has added "dry gas" to his/her gasoline tank in the winter to deal with condensation in the fuel supply has witnessed alcohol's ability to attract and hold water molecules.
In both cases, the lost of water inside of the cells results in the loss of something known as turgor pressure. Turgor pressure is the pressure inside of a cell that pushes the plasma membrane up against the cell wall. Loss of turgor pressure causes wrinkles in the membrane. It also causes the cells to shrink. Some of the cells cannot handle the pressure difference and implode. Those that survive are not able pass nutrients and waste products as freely as they would be able to do in a less hypertonic solution.
With that said, how do we reduce O
2 demands when pitching? We do so by pitching a high krausen. In the case high gravity wort, we pitch a larger number of cells at high krausen in order to account for the fact that many cells may not be able to handle the osmotic pressure.
Finally, why do commercial breweries use pure O
2? Well, most commercial breweries repitch bottom-cropped yeast. Bottom-cropped yeast is taken after the cells have reached quiescence; therefore, they have low ergosterol and UFA reserves. Another reason why commercial breweries use pure O
2 more than likely has to do with efficiency. Injecting pure O
2 is definitely more efficient than pumping air into wort. Time is money and so is energy.
You know the drill. Basically the OP had asked for some advice and about 10 really nice and helpful comments were left and invariably someone had to say, "... If you don't do it this way your beer will suck..." Which is something that seems unnecessary to me.
Friends don't let friends read or post on HBT.
Topic: Anybody Brewing Great Beer with Manual Aeration? (Read 10671 times)
