Originally Posted by mysteryberto
I thought all the CO2 would escape before you had a chance to switch caps and had heard of people freezing bottles before swapping caps. Does the cap swapping tip also work for beer?
Sorry for such a lengthy response, but I have been down this road before, so here's my experience.
Once the soda is sufficiently carbed, switching caps is like opening and closing a bottle of soda from the store, which people do all the time with 2 liter bottles. Eventually it will go flat, but you can recarb it again if necessary. Like soda from the store, the colder it is whenever you open it, the less C02 you'll lose. Freezing it won't help- although the colder it is the less co2 it will lose, freezing a carbonated liquid will force out the co2, so if you open it while it is frozen, it will be largely flat when it thaws out.
Beer is trickier because every time you open it, you run the risk of oxidizing it. In other words, although you can open and close soda repeatedly- as we all have done with 2 liter bottles of coke, this doesn't work as well with beer and wine. If you carb beer in a 2-liter bottle, you need to make sure to squeeze the bottle and force out all
of the air before you put on the carbonator cap. That way, once you shake it to carbonate it, you won't be oxidizing it in the process. I sometimes draw off a 2 liter of beer as a test sample before kegging and carb it with the carbonator cap. I leave the cap on it, and whenever I open it, I make sure to squeeze out the 02, replace the carbonator cap, and then hook it back up to the co2 tank and reinflate the bottle at 10 psi or whatever I have as my keg serving pressure. The purpose with hooking it back up is not so much to carbonate but to keep it from oxidizing. With this method, it keeps longer than say a 40 ouncer you have opened, but it is not very efficient because you use more co2 this way, not to mention that it'll oxidize eventually even with this method because whenever you pour the beer, o2 is coming into the bottle to replace the beer that is pouring out. The more you drink, the more head space you have, and thus, the more co2 you'll need to use each time. I don't mind this for a small sample that I consume in a few days, but if I did this with an entire batch, I would be constantly refilling my tank. You could forego replacing he o2 each time you open it, but as we all know from kegger parties with a hand pump, it will skunk very quickly.
Theoretically, you could do smaller quanities in 20 oz plastic bottles and replace the cap with regular caps just after carbing, which I have tried. The risk of oxidation would be smaller because co2 is heavier than air, but once you carb a 2 liter bottle with a carbonator cap, you'll see that this method is far too labor intensive. I tried this once and found that although carbing a 2 liter is much quicker than force carbing a keg, there is a significant amount of shaking involved. Thus, if you used 20 oz bottles for a batch of beer of any size, it will be far more labor intensive than either kegging or bottling with priming sugar. In sum, I have found that although force carbing beer in a 2 liter is nice for sampling a test amount before kegging or bottling, the carbonator-cap method is too labor intensive for less than 2-liters, and 2 liter bottles of beer are just too large in general, so you end up wasting beer because it oxidizes before you finish it, or you waste a lot of co2 to try and keep it fresh. I can finish one 2 liter bottle before it oxidizes, but doing that more than occasionally would reak havoc on my health and probably my job and marriage. That's a lot of pressure each time I open a beer (no pun intended).