Monday, September 6, 2010

Carbonated Grapes

Ages ago, I took a road trip from Boston to the __ folk festival in NY.  On that road trip, we had a cooler of food in the back seat.  We wanted it to stay cool for as much of the weekend as possible, and there was an ice vendor down the street so we were able to get dry ice.  We put dry ice over the bottom of the cooler, covered it with water ice, put frozen stuff on that, then a shelf, then the fresh food.  About the time we hit Sturgis, I was getting peckish and reached into the cooler for some fruit.   I grabbed a nectarine and some grapes.

I bit into the nectarine and almost spit it back out because it registered as rotten, even though I'd bought it not 4 hours before and it was superfresh then.  I tried the grapes and got the same input, but not the same reading on it.  It turned out that the cooler held in enough gas to carbonate the fruit as the dry ice sublimated.  I just couldn't make myself finish the nectarine, even though I tried, because it really gave the sensation of eating food that had started to decompose.  But the grapes?  Fabulous fun.  I don't know if everyone would have the same reaction - I had previously bitten into bad peaches but my reactions to fermented grapes remains entirely positive to date.

Recently, I learned that high altitudes can kill the ability to sense carbonation, as can some anti-altitude-sickness meds (and likely other things as well), which means that we have carbonation sensors in our tongues that are separate from other things.  I think that's pretty cool. And I think of carbonation as another thing we can taste since it registers partly between sensation (hot/cold/wet/dry) and flavor.  It makes sense that some people don't like carbonation given my inability to finish a perfectly good carbonated nectarine due to the association with rot.  Fortunately, I have more positive interactions with carbonation.

Ever since then, I've wanted to try carbonating grapes again to see if I could get it to work. Last night, while picking up some supplies (for key lime cake) I noticed a cooler of dry ice at the supermarket for $1.49/lb and bought about a pound of it.   I tried 3 different containers.

  1. Initially, I wrapped the dry ice in some paper towels, put it under a makeshift shelf, put grapes on top and wrapped it in 3 layers of supermarket plastic bags and stuck it in the fridge on a towel to keep the glass shelf from shocking.  About 4 hours later, there was a smidge of carbonation.
  2. Figuring that a pressure vessel with a relief valve would be better, I stuck them in my pressure cooker.  But it never built up enough pressure to seal well, so the results were kind of paltry there too.
  3. Lastly, I just stuck the remaining hunk of paper towel wrapped dry ice with the grapes in a gallon ziplock and stuffed it back in the fridge figuring that if it did explode from pressure, it wouldn't do much damage.  And if the grapes froze instead?  I like frozen grapes too.
The grapes in the ziplock seemed to work the best. It didn't take a lot of dry ice, either.  I totally recommend carbonating grapes for a funky party treat, where putting it in a cooler with a tight fitting, but not locked, lid would probably be the best of the options.

UPDATE: If you try this, and want to share, don't do it more than a day in advance, and try not to freeze the grapes. The frozen grapes are good frozen, but not if they thaw out, and the CO2 seems to encourage browning as well (seeing as it feeds plant life, that makes sense). I did vinegar rinse (swish in 1part vinegar/3 parts water, rinse, dry) all my grapes before carbonating to be on the safe side and they're still looking a little miserable two days in. Some still look ok and they are still carbonated but the bag is no longer puffed up.

SAFEY UPDATE: If it wasn't perfectly clear - don't confine dry ice in anything that won't leak at least some, or pop open harmlessly at a low-ish pressure. Soda bottles? Right out. They will blow up into bits of shrapnel. Fun outside, not so much in your fridge or your face. Stick to flexible things or unsecured lids. See comments for technical details if "don't" is insufficient for your rebellious nature.


West/CJ said...

Those grapes sound really good. I've put them on my list of things-to-try this year.

pswett said...

You should be careful confining dry ice: if it goes above the triple point pressure of 75 psi it turns to liquid and the sublimation turns to evaporation, with a substantial increase in rate. This will blow up just about anything you encounter in civilian life due to the 800 psi vapor pressure.

You can use this to good advantage with soda bottles; a Gatorade bottle in particular makes a deafening report and polyester shrapnel.

I carbonate beer fairly often using modest amounts of pressure from a regulated CO2 cylinder, and it's generally a Henry's Law situation, but can take a week to equilibrate. To speed it up, you use a high pressure initially, then lower it closer to the anticipated equilibrium. Beer is usually 4-7 psig at 40F.

Finally, you could probably increase the intensity of the sublimation and hence carbonation by taking a hammer to your dry ice pieces, that will increase surface area and incident radiation, and consequently the CO2 partial pressure in the cooler.

CrankyOtter said...

The hammer is a good idea. It probably only needed a few pea sized pieces in the ziploc. By the time it got to the ziploc bag it was fairly small, about the size of a beer coaster. The thing was fully inflated, but never blew out. After i opened it the first time, there wasn't enough gas to repressurize.

I tried that because I figured the ziplock would leak sufficiently, or blow up at a low enough pressure not to damage much. Same thing with the unlatched styrofoam-n-plastic cooler. The one we used was a giant one with a hinged lid that we pushed shut but didn't latch. And my pressure cooker would have, in an emergency, blown out the gasket as it's 5th defense against blowing up, had the regular valve not worked fast enough.

But thanks anyway for the warning. I don't want someone getting hurt trying to ruin their fruit. We used to blow up soda bottles in college with dry ice we got from the chemistry building, then put the rest in the wading-pool-hot-tub to make bubbles. Do you know what pressure the soda bottles fail at? I never tried gatorade bottles, but a girl needs goals.