Originally Posted by OHIOSTEVE
way way way over my head......here is my plan for this.... brew 10 gallons of KBBA and pitch this into 5 gallons and the fresh yeast into 5 gallons...treat em both the same and see if there is a discernable difference.
While the process requires attention to detail, plating yeast is not difficult (a petri dish partially filled with solidified wort or another culturing medium is known as a "plate"). I plated my first yeast culture after brewing my third or fourth batch of beer. However, that was back in 1993 when the state of commercial yeast in the amateur brewing community was fairly dismal.
Plating requires extreme attention to sanitation. I make my own plates and slants from 5 degrees Plato (1.020 SG) hopped wort and agar (a gelatin that is made from seaweed that remains solid at room temperature). Unlike starters, plating and slanting gelatinized wort should be autoclaved to render it absolutely sterile. While most microflora are killed at temperatures above 150F, one has to take the temperate up to 250F for at least 13 minutes in order to kill spores. This process is accomplished using an autoclave (I usually autoclave plating and slanting media for 15 minutes). An autoclave is little more than a laboratory-grade pressure cooker. One can use a normal pressure cooker as an autoclave in a home setting. I know that some amateur brewers only boil their plating and slanting gelatinized wort, but I do not recommend that practice. If one wants to produce plates and slants that will reliably keep for months in a refrigerator before being used, one should autoclave one's plating and slanting media. A small pressure cooker can be purchased fairly cheaply.
Plating is usually performed within the confines of a laminar flow hood in a laboratory setting. The air inside of a laminar flow hood is under positive pressure to keep anything from settling onto the plates (the air source is filtered).
A plate being streaked in a laminar flow hood
The tool that is in the right hand of the scientist shown above is known as an inoculation loop. A disposable inoculation loop is being used in the photograph. I use a reusable loop that is made from nichrome wire. A reusable loop has to be heat sterilized using a Bunsen burner or an alcohol lamp before being used (the loop is heated in the flame until it glows). An alcohol lamp is much more practical for a home-based lab because denatured alcohol is nowhere near as explosive as propane.
A slightly bent reusable nichrome wire loop
In a home setting, one can plate over a clean, well-sanitized surface using only an alcohol lamp or Bunsen burner, as the air around the burner is rising. However, all transfers need to be performed within a few inches of the flame.
The basic yeast plating process is known as a four quadrant streak. The process is started by heating the loop until it glows. The loop is then dipped into the yeast culture to be plated, which will immediately cool it to the temperature of the culture. One then lightly draws a zigzag pattern on one quarter (quadrant) of the plate with the tip of the loop. The loop is then heated until it glows and cooled on a spot on the plate that has not yet been inoculated (I leave a small area in the middle of the plate untouched to use for cooling the loop). The plate is rotated ninety degrees, and the next quadrant is streaked by overlapping one's zigzag pattern with the pattern in the first quadrant. The third quadrant is streaked by once again heating the loop until it glows, cooling it on an untouched area of the plate, and overlapping one's zigzag pattern with the second quadrant. The process is repeated with the fourth quadrant; however, one must be careful to only overlap the third quadrant with one's zigzag pattern. The plate is then covered and allowed to incubate at room temperature (I store the plate in a clean well-sanitized container while it is incubating). What one is doing with this process is diluting the culture.
After incubating the plate at room temperature for a couple of days, the first quadrant of the plate will usually have a solid line of microflora where one drew the zigzag pattern on the plate. The zigzag pattern will start to have gaps in it in the second quadrant. By the time that one gets to the fourth quadrant, there will be well separated individual dots. These dots are referred to as "colonies." Each colony is composed of the offspring of a single yeast cell.
An incubated four quadrant-streaked plate
Yeast colonies are fairly easy to identify from other microflora. They are creamy white in color and round in shape. Anything that is fuzzy or non-creamy white is a nasty that one does not want in one's beer. When selecting a yeast colony for propagation, one should select only colonies that exhibit good morphology, that is, colonies that have a nice round shape. Non-round colonies tend to be genetic mutants. One wants to pick an average size colony to transfer to a slant. A slant is a screw-cap culture tube that contains the same gelatinized wort as one's plates. The culture tube is positioned at angle while the gelatinized wort is cooling; hence, the name "slant."
Screw-cap culture tube
A slant is inoculated using the same sterile technique that was used to streak the plate. The loop is heated until it glows and cooled on an area of the plate that contains no visible microflora growth (I often use the same area of the plate that I used when streaking it). A yeast colony is then scooped from the plate using the loop and streaked onto the slant (just smear it on the surface of the slant). The culture tube is capped and allowed to incubate at room temperate for a few days before being stored on the refrigerator. The slant contains what is known as a "single-cell pure culture" because it was grown from a single yeast cell.
A properly grown starter from a slant will be significantly purer that anything that one can acquire commercially in the homebrew trade. I brewed for ten years using only home lab isolated and propagated yeast. My beers were significantly cleaner tasting than those of my peers who used commercially-produced yeast. My batch-to-batch quality control was better as well. Yeast is the most important ingredient in brewing; therefore, it should receive the most attention in the brewing process.