oxygen and bottling
 

So I was just reading through a couple threads regarding oxygen barrier caps (over in equipment & bottling) and it seemed everyone was concerned about O2 left in the airspace in the bottle. My brewing science questions are 2-fold (and a half): how much oxygen is actually needed to spoil a beer (is there enough in the airspace)? Does any O2 seep into the bottles from outside?

To answer your last question, no... no air will come in from the outside if the cap is sealed correctly. I've never used the O2 barrier caps and have never had a problem with oxydation. One thing to do is to bottle like this:

-Fill the beer bottles with beer leaving the appropriate amount of head space (bottle filler).
-Place a sanitized cap on top of the bottle, but don't cap it (yet).
-Wait a few minutes to allow CO2 to escape from the relatively flat beer. It's generally enough to fill up the headspace and blanket the beer in CO2. Then cap.

You shouldn't need to worry about O2 then. As for how much O2 results in the off-flavor of oxydation... you got me.

Since we are on the topic of O2-absorbing caps, I have always wondered about the science behind how these work. I have always seen these things packaged in plain old plastic bags. So the caps are always exposed to oxygen - how can continually absorb O2?

I heard that they have to be wetted to activate them (meaning that you can't sanitize them before using them, if this is correct). Anyways, if this is true, I would love to know the chemistry behind this.

To the OP -- I believe that there is always a small chance that O2 can seep into the bottles, but only for beers that you age for > 6 months (more like on the timespan of years). Regarding how much O2 is needed to spoil a beer depends on the style. Big, robust beers with lots of dark malts have a lot of natural anti-oxidants in them. Pale, thin, delicate beers spoil very quickly with only small amounts of O2. Bottle conditioned beer are also more resistant to O2 because active yeast will consume it; beer that is fined or filtered, then packaged without yeast stale more quickly.

I have something to add about 02 absorbing caps I heard on Basic Brewing Radio. Dont remember the episode. They contacted the manufacturer about getting the caps wet. Apparently, the reaction is very slow. It takes a few days for the cap to fully activate and do its job. Therefore, you CAN soak these caps in sanitizer, or spritz them. The reaction will not take place in the 20 minutes or so it takes to fill and cap all the bottles.

I would sure love to know how these things work then. That makes even less sense now. :drunk:

I'll try to dig up that podcast

I have heard that a small amount of oxygen in a beer that will be bottle conditioning isn't that big of a deal because the yeast can absorb a small amount when fermenting the sugar. I have no idea how true this is but it seems logical. Also, are you guys flushing your bottling buckets with CO2 to avoid oxygen pickup in that transfer?

I think the major concern comes when bottling a force carbonated beer. I always flush the bottles with CO2 before filling and bottle on foam so I know there is no oxygen exposure.

I found this that seems to explain it. It seems that they incorporate an O2 absorbing substance, e.g. ascorbates, sulfates, and/or iron compounds in PVC. The substance slowly absorbs oxygen over time.

So my question is why don't they just go bad sitting on the shelf at the LHBS? They are constantly exposed to oxygen. They aren't even packaged with a dessicant, if moisture is a necessary component. I wish I had access to a high precision dissolved O2 meter to try some tests.

I've never really looked into them. Maybe they do go bad... maybe there's an expiration date and optimal storage conditions (temperature and relative humidity). Perhaps there is a certain relative humidity level for them to be actively absorbing oxygen... and that could be 99%, which is present inside a bottle, but rarely in the air.

Anyone on here ever use them? Does the bag have storage instructions or expiration date?