Sunday, March 16, 2008

An interesting observation

I bottled my garage-lagered pilsner tonight. I think this is going to be a very fine beer.

As I was transporting bottles, I noticed a very interesting phenomenon. One I had never noticed before.

If you take a bottle of beer and tap it sharply with your finger, it makes a clear ringing sound. A sound you would expect to hear.

However, if you do the same thing to a bottle of beer that has just been bottled, the sound is a dull thud. There is no ring to it. It sounds as if the bottle is filled with sand.

I have some beer that was bottled 3 days ago and it has partially regained the ring.

So, what causes this? Well, I'm not sure.

The just bottled beer is not carbonated yet and it contains a fair amount of suspended solids. That may be the cause, but I will know more tomorrow. I am going to check again tomorrow to see if allowing some of the solid to settle out makes a difference.

UPDATE: I checked the bottles today and the ring is back. Since it is too early to carbonated, I suspect the sound has to do with suspended solids. Apparently, the colloidal suspension the results after bottling has a dampening effect on the vibration of the bottle. After settling out for 24 hours, the dampening effect is gone. Interesting.

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Check back in the next few days for my most labor intensive post ever. It's a journey of sorts.

1 comment:

Susie said...

I would guess that the pressure built up from the carbonation would increase the resonant frequency of the bottle? A rough analogy would be to a kettle drum membrane being tightened to raise the sounding pitch?

It is really kind of fascinating to think that the pressure of carbonation is enough to change the sounding pitch of the glass bottle though! I don't think I would have expected it to have a significant effect, because the glass of a bottle seems so solid.

I wonder if you could calibrate the pitch of the bottle to act as an indicator of how much fermentation has happened... then you could (theoretically)calculate the % alcohol, as the molar ratio of alcohol to CO2 is a more or less a set number. That would be completely ridiculous, but so damn cool. (What can I say, I'm an acoustics nerd turned food chemistry nerd, and this got me really excited...)

Anyway, I would predict that the pitch drops back down once the bottle is opened and the pressure let out.