# Will peroxide kill yeast?



## philistine (13/2/15)

Hey All,

I've got a batch fermenting atm thats blowing off a shit load of krausen. I've set up a blowoff tube that goes into a 5L demijohn and there's about 300-400ml of peroxide/water sanitzer solution covering the tube.
I just went and had a look and at the bottom of the demijohn there's a thick layer of what looks like a really nice clean healthy yeast cake.
Is that yeast still alive?
Ive had this blowoff set up quite a few times now (usually always with peroxide) and whenever I get a really crazy ferment and a decent amount of krausen gets thrown out of the fermenter - I swear the blowoff container starts to ferment itself and starts growing it's own krausen.

Just wondering if its worth washing and saving...?


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## Yob (13/2/15)

Why do you use peroxide?


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## philistine (13/2/15)

no reason in particular... its cheap ($3 a bottle from woolies)
I usually use it coz its convenient - i use it as a spray sanitizer while Im setting everything up, then tip whatever's left into the blowoff container to cover the end of the tube.

I've used sodium perc. a few times and noticed the same thing (ie. when there's a decent amount of blowoff, the blowoff starts... well.. blowing off)


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## philistine (13/2/15)

i just googled 'peroxide and yeast' and apparently yeast causes hydrogen peroxide to break down


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## Black n Tan (13/2/15)

Hydrogen peroxide has the chemical formula H2O2. It is a highly reactive oxidising compound (reactive oxygen) and at the right concentrations will kill yeast and bacteria. So if you want to harvest the yeast from your blow off, peroxide or other sanitisers are not the way to go. I have no idea what concentration you are using the peroxide at, but I assume you are using it to sanitise your blow off water. As such you should not expect your yeast that has come in to contact the peroxide to be in good health.


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## Feldon (13/2/15)

I recall the breakdown products of hydrogen peroxide are oxygen and water.

So if the yeast are growing in the demijohn it may be because they are multiplying in the presence of all that free oxygen.


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## philistine (13/2/15)

(after posting this thread) i was reading something about school science projects mixing yeast with peroxide to see how much foam it produced.. so Im thinking the foam Im seeing is just that - foam.. not krausen... Still, im gonna give it a go and wash it then do a little experiment to see if it'll grow in a litre of starter...


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## Ducatiboy stu (13/2/15)

Peroxide makes a great sanitiser because it tries to oxidise everything it come in contact with. And it leaves no residue.

Probably the ulimate santizer when you look at it.

And yes, it will kill your yeast stone dead


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## MHB (14/2/15)

Maybe - It will depend how much yeast and peroxide are in the blow off jar, I doubt you added pure peroxide, so it may have killed the first of the yeast to come across, but the peroxide is consumed during the reaction.
If there is more yeast than peroxide available to kill it then the later yeast will be alive, mind you if its an open jar, its probably got lots of other bugs living in it by now, so I wouldn't really be using it as a re-pitch - that's just asking for trouble.
Mark


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## Mr. No-Tip (14/2/15)

I have no idea but am interested in a definitive answer. Can you make a small starter and find out?


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## Yob (14/2/15)

Microscope and varying concentrations, a starter won't tell you if you've damaged, how much you've damaged etc, I can't see it doing them any good really


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## Camo6 (14/2/15)

I did similar a while back but used star san in the blowoff bottle. As an experiment I threw it into some leftover wort. No activity at all. Now I only use sterile water in the bottle.


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## TOF (21/5/15)

I know this is an old thread but be very aware of what strength of Peroxide solution you are using, the common bottle from the supermarket is 3% by volume and is quite safe to use. Pharmacies have stronger mixtures but only at 6%, Peroxide is used in certain industrial applications at up to 100%, at this strength it has the capability to dissolve most fabrics before you have time to react to the pain. Beware, Ken.


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## MHB (22/5/15)

Even industrial "100%" peroxide has stabilisers added usually sodium-thiosulphate, you will I am sure have seen those jet back packs that some times fly around at shows and the like. The fuel is 100% H2O2 it is being pumped into a chamber full of silver mesh, the jet effect is the H2O2 breaking down into H2O + O2 and releasing a lot of energy so the water flash boils into steam - coming out with enough force to lift the pilot.
Point being H2O2 is very reactive and in anything like high strengths very dangerous, the products sold for sterilising are very effective and if you want to reuse yeast you don't want it or any other steriliser any where near your yeast.

If you want to crop yeast from the blow off tube, put an interceptor bottle in line. Just a sterilised bottle with a two hole bung, pretty common in labs for trapping all sorts of liquids and gases, should work a treat and not harm your yeast.
An example being bottle B in the following. but note the flow would be from C-A, the long tube being the inlet to the trap and the short outlet going to an airlock.
Mark


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