Why is the soda fountain foamy?

August 29, 2012 1:55 PM

Two soda fountains. Two paper cups full of ice. The first fountain consistently dispenses soda into its cup with very little foam. You could fill it all the way up to the top without having to stop once to let the foam subside. The second consistently produces a very foamy drink, so that you have to stop, let the foam subside, fill again, stop, start, etc. until your cup is full. What's the difference? Why the foamy soda?

Notes:
Same soda: diet coke.
No noticeable taste difference in the dispensed drinks.
Not the same ice: each fountain produces it own ice.
Not the exact same cups, but the same type: waxed paper.

Also, I have read the poured soda foams less if you wet the ice first. I have tried this on fountain #2 and it is not the case.

posted by stupidsexyFlanders to science & nature (9 answers total)

Balancing the mixture of CO2 and beverage can be a royal pain in the ass. It's a combination of pressure in the keg, the pressure in the CO2 tank, the length of the hoses, the inner diameter of the hoses, temperature across the length of the hoses and other annoying things.

I'd assume that the owner of fountain #2 has not found the right settings yet.
posted by sparklemotion at 1:58 PM on August 29, 2012 [3 favorites]

Just came to nth CO2 mix.

Makes all the difference.
posted by Ruthless Bunny at 1:59 PM on August 29, 2012

Subtle differences in the texture of the cups can do this too. My parents have one glass that looks almost the same as all the others, but it is older and rougher inside and will absolutely flatten a soft drink in a minute or two.
posted by crabintheocean at 2:10 PM on August 29, 2012

Yep, CO2 mix.
posted by greta simone at 2:13 PM on August 29, 2012

The process of balancing the mixture is called "brixing" the fountain. You use a device that measures the ratio of carbonated water to syrup. Too much one way = fizzy. Too much the other way = flat. See example here.
posted by DaddyNewt at 2:28 PM on August 29, 2012

You could determine whether the cup and/or ice has any effect by mixing & matching the source of the cups, ice, and soda, e.g., cup from fountain 1 + ice from fountain 1 + soda from fountain 2.
posted by DevilsAdvocate at 2:45 PM on August 29, 2012

Assuming the CO2 mix is the same, is it possible that the foamy fountain has a restriction or more complex path in the output nozzle that is agitating the soda as it is dispensed?
posted by bz at 4:11 PM on August 29, 2012

When I was a teenager, the diet cola always did that. And so everyone (in the places I worked) would stick a finger in the cup while filling to keep it from foaming up. (OMG, I cannot believe that was the recommended solution and it icks me out now. That's how we filled glasses for customers.) Anyway, my bosses told me that you couldn't get the CO2 to work right for the Diet unless you screwed it up for the other drinks. I guess there was just one CO2 tank setting.
posted by Chaussette and the Pussy Cats at 10:47 PM on August 29, 2012

Colder water will hold more dissolved gas. I wonder whether the two fountains dispence at the same temperature (before ice)
posted by lake59 at 1:23 PM on September 1, 2012