Just a quick update....It seems like washing the yeast with chlorine dioxide was a success! I used some yeast that I knew was slightly contaminated. WoodlandBrew was kind enough to run some test on my yeast before the "wash"...http://woodlandbrew.blogspot.com/sea...l/lab%20report
I used the WL002 for a Brown Porter. Racked into the kegs and it tasted great. No sourness at all. Just to confirm my results I will send him some of my "washed" yeast for comparison.
Here is a what a brewing supplier says....
WASHING OF YEAST SLURRY WITH OXINE: Stabilized ClO2 (Oxine) will effectively kill unwanted bacteria in yeast at 20 to 40 ppm, while leaving the culture yeast unharmed. Because of stabilized ClO2's unique action, it does not have the drawbacks of phosphoric acid. It does not form chlorophenols (which contribute to a much feared medicinal character in products) in the presence of organic materials.
YEAST WASHING METHOD: Normally, an initial washing at 20 to 40 ppm (20 ppm for homogenous yeast, 40 ppm for "clumpy" or highly flocculant strains) is effective against most Lactobacilli and Pediococci species. This "wash" is done by adding stabilized ClO2 directly to yeast slurry on a volume/ppm basis. It does not need to be activated as the pH of the yeast slurry is low enough to convert to ClO2.
Stabilized ClO2 is supplied at a concentration of 20,000 ppm or 2% Chlorine Dioxide when activated. Therefore, on a volume basis, one could essentially make up with one gallon of stabilized ClO2 concentrate, one thousand gallons of solution at 20 ppm. By this method, we can also assume with one gallon of concentrate to make up one thousand gallons of yeast slurry at 20 ppm. It is impractical to measure the concentration of ClO2 in the presence of yeast, so the dilution must be made based on the strength of the concentrate (20,000 ppm).
Yeast slurry should be thin enough to allow for homogeneous mixing, usually 20 to 40% solids. The killing action of stabilized ClO2 is very fast compared to the traditional phosphoric acid wash. Only 15 to 30 minutes need be allowed for effective bactericidal effect of stabilized ClO2, with no resultant stress on yeast cells.
YEAST WASHING DOSING RATE: For regular washing of homogenous recycled brewers yeast, a 20 to 40 ppm wash for a minimum 30 minutes to 5 hours prior to pitching. Mix 1 to 2 ml of stabilized ClO2 concentrate with each liter of yeast slurry. Agitate thoroughly during the process.