Wednesday, February 23, 2011

Headspace: I'm proud to say, I also have gas.

Remember when sneakers had
crazy gimmicks? Oh wait...
I felt a little left out with Gene's last post. Being the less fully equipped brewer in this tale of two: I don't have any hose problems, mysterious off flavors from improper keg washing, or other mechanical troubles. What I do have is lots of gas (that I make myself - heh.) My fascination with CO2 tanks ended around 2 years after Reebok Pump sneakers went out of fashion.

Since you don't need pressure to dispense beer from a bottle (just gravity and thirst,) I'm just going to talk about carbonation. When bottling with priming sugar there's really only one factor that you can change to affect the amount of carbonation: headspace.

I actually didn't know anything about this topic until I received my first issue of Brew Your Own magazine last week. In the March/April issue Ashton Lewis has an excellent answer to a reader question on the topic of carbonation space. That question is longer than this entire post, so let me summarize it for you:

"Does the amount of airspace you leave in the top of the bottle matter?"

Summarizing the answer is "Yes; yes it does," but I'm guessing you wanted a bit more than that. Without really caring about why it worked, but only that it did work I had some hunches about this that I bet many of you share.

Hunch 1: The air at the top of the bottle includes oxygen that the yeast need in order to make gas.
Hunch 2: The amount of air doesn't matter at all and is only there to prevent the beer from rusting the cap.

After reading the article, it's safe to say that both of these are dead wrong. Hunch 1 is not true because brewer's yeast operates anaerobically (that means without oxygen, not without exercise.) Hunch 2 is wrong because the inside of the caps are plastic coated (although the BPAs have more of a chance of leeching in if it's touching the liquid.) So what's the right answer?

A certain amount of head space is required to create the right outside pressure on the liquid so that CO2 created by the yeast is dissolved into solution rather than remaining as a gas. If there was too much headspace the CO2 would have plenty of room to move around and wouldn't get dissolved, too little and the cap might blow off from the pressure. That's less technical than his explanation, but if you want that kind of detail check out the magazine (Brew Your Own.)

So what's the lesson? Don't fart if you're in a pressurized space suit. Also, leave the recommended inch of head space in each bottle if you want a foamy home brew.

I hope you enjoyed this post (it had more poop jokes than usual!) Know a better reason for the headspace? Please leave any comments below! 

1 comment:

  1. I definitely agree with that. Not deviating from the recipe is probably
    also a good idea for new brewers.

    ReplyDelete