Hey Joe,
Glad you got a kick out of my experiences with White Labs pitchable yeasts. I still have a couple of tubes in my brewhouse fridge-a-merator!
A little more on flocculation which is an interesting process and very important to mead and beer making.
The text is from a set of transcribed notes I had from my Microbiology 510 Course at Cal Poly Pomona. The course was called Applied Microbiology and we actually made beer, mead, wine, sauerkraut and yogurt in the class. We had a big party at the end, and my Vin Rose Wine was voted the best. Our professor was East German with a very thick accent and she provided the knackwurst and buns for our sauerkraut. It was a good party!
---- Notes:
Flocculation of yeast is very important in production of beer that causes the yeast to precipitate out into the bottom of the fermentation vessel at the end of the fermentation cycle. As a result the yeast may be harvested from the bottom of the fermenter and used in a culture to grow colonies in sufficient numbers for the next fermentation, while the beer may be matured without the need of a centrifugation step.
In a best case scenario brewing yeast will not flocculate in the beginning of fermentation, but only after all the nutrients have been metabolized. However depending on the conditions, the yeast may flocculate too early or too late, leading to improper fermentation or the need for centrifugation. In order to improve the control of flocculation during beer production the genetic mechanisms of flocculation are being studied.
Yeast flocculation requires the presence of at least two types of molecules on the cell surface. One type is mannans (carbohydrate chains), which are produced by the gene products of the MNN genes and are present on the cell surface at all times.
The other type is flocculins (sugar binding proteins), which are the gene products of the FLO genes, that are activated only after depletion of nutrients. The flocculins bind to mannans on the surface of neighboring cells leading to the cross binding of cells and ultimately the formation of flocs, each consisting of several cells.
Because the surface to volume ratio of the aggregated cells is reduced, the flocs precipitate out much faster relative to the free cells. ----Another note is that this flocculation process is similar in effect to the micro-agglutination process used in Immunology and Serology for type and cross-matching of blood for prevention of transfusion-reactions.
If you can visualize some of those little Styrofoam balls from the local art supply store that have a bunch of long sharp needles sticking out from them. Toss several of them together in a bunch, and at a very basic level you have a rudimentary model of a floc.
Cheers,
Oskaar