Sterile yeast rehydration water

[foles]

Anybody every had contamination from rehydrated dry yeast ? I usually give a cup a quick boil in the microwave, let it cool to about 35C then rehydrate. I've had contaminated beers while using this method, despite my wort passing the wort stability test. Given pitching yeast is usually a likely cause of contamination, I am starting to think I'm not sterilising my water properly. May have contaminants from my carbon filter that need a good 15-20 min boil first. Its funny how the same rules or sterile starter water don't seem to apply to rehydrating yeast?

Thoughts?

 

[harebearva]

I personally can't say for sure that I haven't, but I feel there are many more likely opportunities for infection. Some people claim that once water reaches a rolling boil, it is sterile, but I go about 1 minute at boiling. I pretty much do the same process you do. I boil water 3 minutes in the microwave then chill and rehydrate yeast. Not sure of your complete process but I soak my scissors in star san and spray the yeast pack as well. I also cover it with foil that I have sprayed with star san as well. Tough part about infections is tracking down the culprit. I usually end up soaking EVERYTHING in PBW to be sure.

 

[j1n]

i doubt that's the cause of the contamination. Pasteurization of liquids @ 160 degrees for 30 seconds kills 99.99% of bacteria.

Also i dont boil the water when i rehydrate i just set my electric kettle to 170 and then wait for the water to cool to 100 before adding the yeast. Many here also heat the water to 160-170 for when they hydrate and add gelatin to clear the beer.

 

[trentm]

Anybody every had contamination from rehydrated dry yeast ? I usually give a cup a quick boil in the microwave, let it cool to about 35C then rehydrate. I've had contaminated beers while using this method, despite my wort passing the wort stability test. Given pitching yeast is usually a likely cause of contamination, I am starting to think I'm not sterilising my water properly. May have contaminants from my carbon filter that need a good 15-20 min boil first. Its funny how the same rules or sterile starter water don't seem to apply to rehydrating yeast?

Thoughts?

Sterilization is a term that often gets misused. Palmer defines sterilization as: The elimination of all forms of life, especially microorganisms, either by chemical or physical means. In fact water cannot be sterilized by boiling. Although boiling water for 15 minutes will kill most vegetative fungi and bacteria, and inactivate viruses, it is ineffective against many bacterial and fungal spores. So technically when we boil water we are sanitizing it (To kill/reduce spoiling microorganisms to negligible levels - Palmer). That said, for most brewing applications sterilization is not required and sanitization is adequate. However, in some instances, when working with yeast sterilization is necessary. This is not the case when working with a single step starter because the yeast will quickly out compete any organisms that may have escaped your sanitization process. With stepped starters, sterilization may be needed because with each step the lag period may allow any unwanted organisms to room to compete. After all that, I really don't have experience with dry yeast but I would assume that good sanitization techniques should be adequate. Think through all your processes to make sure all your equipment is clean and sanitized, consider increasing your boiling time and pitch your yeast as soon as they are rehydrated.

 

[SpeedYellow]

Seems highly unlikely that your boiled water is causing the problem. Just make sure its container is sanitary, of course. You may want to cover the rehydrated mixture during the process if you're really worried about it.