How long to deoxygenate water?

I've searched the forums and the web and can't find a substantiated answer to a simple question: how long do you need to boil water to reach a reasonable level of deoxygenation?

I know boiling can not totally remove O2 from water. However, there has to be some general guidelines on this matter. I'm particularly interested in long-term yeast storage, so I don't want to over boil and condense materials either. I'd sincerely appreciate informed replies.

I don't have a good answer for you but I do recommend searching the terms yeast storage on the forums. Should be quite a few threads.

The solubility of a gas in water is directly proportional to it temperature, with increasing temps = lower solubility. The solubility of O2 is well determined:


As for how long it takes, the answer is "its complicated". The off-gassing rate is determined by a combination of the surface area available for gas-exchange (i.e. the larger the diameter of the pot = the larger the area of water exposed to the air = the faster the gas exchange), the partial pressure of O2 in the water and the partial pressure of O2 in the air.

That's the bad news.

The good news is that as you approach a boil, solubility goes down to near-zero, while the surface area increases greatly (due to the steam bubbles, which act just like the air above the pot). Meaning, that a short boil will quickly deoxygenate the water (2-3min should work, unless you've got a huge volume of water). A word of caution - deoxygenated water will suck O2 out of the air quite quickly; to minimize this make sure you cool quickly, use the water soon after cooling it, and don't shake it up too much when you're using it.

Bryan

Sincere thanks, Bryan!

For long-term yeast storage, I will be boiling distilled water and pressure canning it for sterility and to maintain the lowered O2 level.

For short-term yeast storage (e.g. harvesting/washing yeast), I purge the headspace in my containers with CO2 to avoid as much oxygenation as possible. With the 15 ML vials I use for long-term storage, purging isn't a viable option, though.

Boil it 20 minutes and put it in a canning jar, just poil the canning jars and lids in the same H2O and you are good to go.

seafra said:

Sincere thanks, Bryan!

For long-term yeast storage, I will be boiling distilled water and pressure canning it for sterility and to maintain the lowered O2 level.

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If your canning, there is no need to pre-boil; simply put in jars, can for 20min like you would any other preserve, and it'll be fine. A major part of how canning preserves food (aside from sterilization) is by removing O2; that's why canned fruit doesn't brown.

Bryan

I wouldn't use distilled water that'll put a lot of osmotic pressure on the yeast.

Bubbling nitrogen through the water will significantly decrease dissolved oxygen levels