Secondary fermentation: using N2O to prevent oxidation

So, from what I have gathered you want to use the smallest possible carboy that will contain your batch when you rack to secondary for settling/secondary fermentation/bulk conditioning. You use the smallest carboy that will fit the batch because you don't want the oxygen in the headspace to oxidize your product.

I am about to brew up a 5 gal. batch of partial grain imperial stout, and the recipe requires the use of a secondary. My (currently only) glass carboy is 6.5 gal, leaving 1.5+ gal of headspace in the top of the carboy. I was thinking, to displace the oxygen in the headspace, that I could "blow in" some N2O (nitrous oxide, also known as whipped cream propellant, or "whipits"). Would this be a prudent procedure to help eliminate the risk of oxidation? if not, should I just buy and boil a gallon or 2 of marbles to fill in the rest of the space? or should I just RDWHAHB and not worry about the 1.5gal of air in the secondary?

advice is much appreciated

Doesn't N2O have more parts oxygen per space than the normal air we breathe?

N2O doesn't break down into elemental oxygen and nitrogen unless its under pretty extreme conditions (like those found in the combustion chamber of your engine, ~7-10 ATM and over 200*C). That's why they use it in food preparation. Whipped cream doesn't oxidize because under normal conditions the N2O won't break into N2 and O2 (otherwise we might have sour-whipped-cream). They also often fill bags of chips with N2O, again to replace the oxygen and keep the product fresh.

edit: N2O is a pretty stable molecule. might not be as stable as CO2, but its close under normal conditions.

Why not CO2? Unless you don't keg and have a lot of access to it.

Edcculus said:

Why not CO2? Unless you don't keg and have a lot of access to it.

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I don't have any CO2 sitting around (I don't keg), but I do indulge myself with a bit of laughing gas every now and then, and as a result I have a few N2O charges just sitting around.

If I settled with CO2 over N2O, could I drop a small chunk of dry ice in the secondary, and let it bubble away to replace the air in the secondary, or is this a recipe for killing yeast and creating off flavors?

How about dumping in a little bit of dextrose?

schadelh said:

could I drop a small chunk of dry ice in the secondary, and let it bubble away to replace the air in the secondary, or is this a recipe for killing yeast and creating off flavors?

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The problem with dry ice is most of it is dirty (as in physical dirt). After the CO2 sublimates, you're left with potential range of impurities that may potentially lead to off flavors.

Yeast are EXCELLENT oxygen scavengers. Use them to your advantage - either don't use a secondary or pitch a small amount of sugar after racking to your secondary vessel to awaken the yeast and encourage oxygen uptake.

But, if you do nothing, you'll probably be fine too.

Remeber to sit down, and I wouldn't use NO2 while dealing with a glass carboy, as you are very likely to drop and break your carboy...Wait, that's not what you mean is it?

worth said:

Remeber to sit down, and I wouldn't use NO2 while dealing with a glass carboy, as you are very likely to drop and break your carboy...Wait, that's not what you mean is it?

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Maybe off topic, but doesn't Guinness use N2O? or is it N2?

Edit: just finished brewing the batch. OG = 1.113 this is going to be a powerful brew!