# Washing yeast with chlorine dioxide



## Dubzie (14/8/18)

In my yeast research I came across a few old posts over on homebrewtalk about people who had successfully "cleaned" infected yeast with chlorine dioxide. Not sure if you can cross link to that forum here, but i can provide the threads.

I've also found the PDF attached that shows how good it is at killing bacteria ect while barely touching the yeast viability. 

Does anyone here use this method? Seems it would be great to treat a vial/slurry before making a starter.


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## MHB (15/8/18)

Have a look at "Water Purifying Tablets" they are sold at camping and outdoor stores. They have the Sodium Chlorate and the Acid in the right ratio to make ClO2, then you just have to work out how much to use. Can be purchases as powder and liquid (2 part mix at need).
Known to be an effective process, the biggest problem for home brewers is measuring accurately, very easy to over/under dose and either not kill the bacteria or to kill everything.
Unless you have a very firm grasp of chemistry and some pretty good measuring equipment I would look at making 1 tablet up in a known volume (say 1 tab/L) and then measuring how many mL you need to get the desired amount of ClO2, just remember storing ClO2 solution can be problematic (needs dark and cold), if you cant test for activity you are guessing.
If you cant measure the amount of ClO2 in solution you would be well advised to make up fresh each time.

Will follow with interest, but still no substitute for keeping the yeast clean, I wouldn't be storing or propagating yeast that was contaminated, potentially most useful for reusing large amounts of slurry.
The last paragraph in the attachment needs re-reading!
_All this having been said, remember that there is no substitute for proper sanitation. The best way to keep undesirable organisms from infecting beer is to keep all the equipment clean, sanitized and unexposed._
Mark

PS
Just had a look on eBay and the two part liquid looks like the best option for making up small quantities.
M


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## Dubzie (15/8/18)

Chemistry isn't one of my strong points and I don't have any measuring equipment. 
100% agree it's no substitute for proper sanitation, i've been looking at it as more of an additive to the process.

Get jar of stored yeast, decant and add solution of 20ppm to the jar.
Let the yeast settle out again (while prepping starter)
Decant solution and pitch yeast to the starter.

Are these Chlorine Dioxide Solutions not the same thing: Ebay
Further googling found this: "chlorine dioxide gas is in fact bubbled through a solution of slightly saline water until complete saturation occurs hence the reason for no further activation being required " Here

With these linked solutions at 24000ppm and 3000ppm, 1ml would treat 1.2L and 300ml respectively @ 20ppm


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## MHB (15/8/18)

I'm not 100% sure how shelf stable it would be once opened, at least with the 2-part ones both the acid and Sodium Chlorate would be stable giving the same concentration of ClO2 every time. If you stored the liquid version cold and dark it should last a fair while but I cant be more precise than that.

There is a very handy little equation that helps with dilution (well its called the standard dilution equation).
C1V1=C2V2
C is Concentration and V is Volume, so if you wanted to make 1L of 20ppm solution from your 24,000ppm stock (remember to keep all the units the same mL and L don't work)
C1 is 24,000ppm, C2 is 20ppm V1 we want and V2 is 1,000mL
24,000*V1=20*1000 gives 20,000/24000 = 0.8333mL.
Or as you said 1mL to 1.2L

Worth noting that the paper you quoted talks about a range from 20 to 50ppm. they are working in a Lab and probably to better standards than most home brewers will be able to achieve, I think somewhere in the middle would be a smart place to start, if not at the higher end, so 35-50ppm might work more reliably the 20ppm.
just playing with the same equation but the other way, what would 1mL/L give us?
24,000*1=C2*1000 gives 24ppm, 1.5mL/L gives 36ppm which is where I would be thinking o starting.
Mark


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## Dubzie (15/8/18)

Noted!

_While phosphoric acid did a respectable job of destroying the bacteria, the viability of the yeast suffered to varying degrees (~14.5% and ~4%). It also seems to have had no effect on the wild yeast. Chlorine dioxide appears to have cleared both slurries of bacteria quite thoroughly, even at the 13-ppm-levels we achieved, without decreasing the viability of the yeast. This was accomplished inside of ten minutes, rather than over the two-hour period required for the acid wash._​
So from the look at it the solution they made: _50 ml activated sodium chlorite (0.5 ml of 8.3% sodium chlorite concentrate, added to 100 ml cold water which had been acidified to pH 3), which was calculated to yield 20-50 ppm in the volumes treated._
which was then added to 1000ml of water + slurry, giving 13ppm?


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## MHB (15/8/18)

Ok, I think I see what's going on, the amount of reagent added should have given 20-50ppm in the whole litre, when they measured it they only found 13ppm.
Just means the reaction wasn't complete and there was still Sodium Chlorate that hadn't converted - at the time of the test. They are speculating that it may have converted later and kept working on some of the contaminants.
If as you surmise they made 100mL of 20-50ppm ClO2 then added that to make a litre the range would be 20/10=2ppm to 50/10=5ppm not the 13 they have measured.
If I get a chance I'll have a bit of a dig through some other references and see if we can get some tighter numbers.

Looks like it might be worth working on, could be a simple way to get much cleaner yeast for repitching.
Mark


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## MHB (15/8/18)

PDF didn't save will try later
M
Its Later
Good read


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## Dubzie (16/8/18)

Ahh yes also read that pdf in my research!


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## MHB (16/8/18)

Then you will note that the second, (MBAA presentation) is over 15 years newer so probably better researched is talking about 50-100ppm concentrations for effective suppression of some of the common beer spoilage organism's.
Depending on what you are trying to achieve, well worth pinning that down. No point in treating a fresh slurry that isn't contaminated, have to hope we aren't contaminating our fresh yeast as we make a starter - if so probably more important to address that.
But might be very useful for improving yeast collected from a brew.
Mark


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## Dubzie (16/8/18)

Thats true!
My current method to over build a starter save 500ml of the starter for the next starter.
My thoughts were to treat the saved yeast before I built it back up in the starter, as nothing is ever 100%.
If all it takes is a drop or 2 of solution, plus the time it takes for the yeast to resettle, while i'm building the new starter then it cant hurt.


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## /// (19/8/18)

The sodium chloride versions are harsh on stainless. We used to fortify with citric acid, but it's pretty dangerous as it releases chlorine gas whilst doing so; breathing it in causes hydrochloric acid in the lungs ... Not good! Once diluted it is great to use


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## Dubzie (20/8/18)

/// said:


> The sodium chloride versions are harsh on stainless. We used to fortify with citric acid, but it's pretty dangerous as it releases chlorine gas whilst doing so; breathing it in causes hydrochloric acid in the lungs ... Not good! Once diluted it is great to use


I should get my solution soon which has already been pre-mixed so it doesn't need to be activated.


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