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Carbonated Fruit in Large Batches

ParkerCook_66639

A food-science professor/friend of mine is wanting to make a large batch of carbonated grapes and is sure that using a pressure cooker and dry ice will work. I told him I'd throw the idea out on the forum for input from everyone. Is this a good idea? Is it safe? Will it work? I've only made carbonated fruit with my whipping siphon so I couldn't help him out.

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seijoed

Grant Lee Crilly interfering with the natural order of things

I'm really glad I didn't want to try that actually.

ParkerCook_66639

@Grant @Tim thanks so much guys!

Tim_Sutherland_52834

Not having any fruit, but some time, I dug up my old chem memories and calculated the pressures in both my 0.5 liter iSi and 12 litre Kuhn Rikon Pressure cooker.

By completely filling my iSi with water I get a 726ml volume, this includes the small volume in the lid above the gasket. The pressure cooker gives me 13,209ml (again including the lid).

Using the Ideal Gas Law, PV=nRT, the molar mass of CO2 of 44.01g/mol, and current room temp (23C or 296.15K) I calculate the pressure in the iSi with one 8g CO2 charge as 616.5kPa (89.4psi), two charges is double the pressure and I have given fruit two charges before - soft berries will deform and hard fruit will retain shape. Ben Krasnow in one of his videos calculates the pressure in his 0.5 litre iSi and gets a higher pressure, but he uses 0.5 litres as the volume.

From my basic understanding a pressure cooker will release pressure once the pressure inside goes over ~15psi. From my calculations adding 24g of dry ice to my 12 litre pressure cooker will only produce a pressure of 14.7 psi, so in theory the pressure cooker will not need to vent. Adding fruit will change the volume of the cooker and the amount of CO2 would need to be reduced accordingly. If by accident I added 30g of dry ice (18.4psi), the pressure cooker should vent the CO2 until the pressure drops. From my reading of a number of MSDS (pages 5+4), the expansion ratio for dry ice is 554 times, much less than the 1,600 times for water to steam. The safety valves should be able to vent the extra pressure without problems (assuming the cold does not effect them). The air temp inside the closed pressure cooker will become lower than room temp which would cause the actual pressure to be less than the calculated pressure.

In theory it should be safe to carbonate fruit in a pressure cooker with dry ice as long as some basic calculations are done before hand. Note dropping a 5lb brick of CO2 in the pressure cooker would not be smart as the calculated pressure would be 1,393psi - this may void the warranty on the pressure cooker.

Whilst I have done many things in my life, a chemist or engineer are not two of them, my numbers may be out and things go BOOM.

grant

Dont do that! You don't want to make a bomb. ANd the fruit does not need that pressure. Once brought back to atmospheric pressure the fruit will most likely explode like when bringing a fish to the surface of the ocean from the abyss.

You only need to:

1) Pack the fruit in a box and cover with cloth

2) Add dry ice to the other side of the box as too not freeze the fruit

3) Plastic wrap the box and store it for several hours of overnight.

Enjoy!

Tim_Sutherland_52834

I don't know if the 15psi the pressure cooker will get to will be enough to carbonate the grapes that you will get the effect you are after. You will need to do a few trial runs to see if the dry ice can carbonate and also time how long it takes for it to work.

The easiest solution would be the carbonate in an ISI to order. Over time the grapes will lose their carbonation and so even with dry ice you will need to do more than one batch during the five hours.

The only potential issue I see with dry ice and a pressure cooker is the cold freezing one or more of the safety release valves.