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This might be considered off-topic, but thought it was worth asking, as I have no idea where else to ask --

I'm trying to make something forcibly eject from a cake. I've done some testing with a can of reddi whip, and I've found that I can get decent distance by restricting the size of the opening. But I'm debating on getting my own whipper, thinking that I can then tint the results, but that I might also be able to charge it more than once to get a more forceful ejection.

Are there any problems with over-charging a canister? In the response to the question about ragged peaks from a whipped cream dispenser, one of the responses said it might be from over-charging the container, so I'm a little concerned. (not that much, as it just needs to shoot out, being pretty isn't necessary, so ragged peaks aren't an issue; the whole thing turning to butter and clogging the canister or being inedible would be)

(I also assume there's a safety margin so it's not an explosion issue if I only double or triple charge it... I seem to remember my mom once double-charging one, when it didn't dispense, only to find out she had clogged it up with home-grated nutmeg; there wasn't an explosion 'til she tried taking the lid off)

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up vote 6 down vote accepted

Charging a whipper two or three times is definitely not going to make it explode; for certain lower-density preparations you're supposed to charge it twice, but even if that weren't the case, consider that one of the chargers holds only a fraction of the volume of the whipper itself (8 g, to be exact), so if the chargers don't undergo explosive decompression then it's definitely not going to happen to the whipper.

As for it possibly turning into butter, that's a more realistic possibly depending on what you're putting inside it. I can't verify whether or not it happens with cream since I've never tried it and probably never will; I wouldn't recommend it, since whipped cream gets very dense to begin with.

But honestly I think your biggest problem is going to be that whipped cream dispensers aren't designed to dispense upward. The instructions are very explicit that you have to hold it upside down in order to dispense; if you hold it right side up then it's just going to vent the gas and make it impossible to get the cream out with opening it up.

Simply stated, the cream is much heavier than the gas, and I believe that whippers don't actually achieve saturated vapour pressure inside. That's why the gas will always eventually end up on top no matter how you orient the whipper; the key to getting the cream out is forcing the gas back down through the cream by depressurizing it, which is why you need to hold it upside down.

So unless you want to eject it from the bottom of the cake, I'm sorry to say that I don't think this is going to work for you.

One alternative you might be able to try is to pre-whip the cream with a stabilizer or make a fondant, then put it into a hollow tube and eject the gas from the whipper into that tube. That way you can guarantee that the "liquid" is actually in the path of the gas, and the gas should propel it upward. I emphasize should; it's going to depend on the density of what you're trying to propel and how good your seal is, and you'll probably have to experiment a little.

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I know it's not going to work spraying up ... I'm hoping that I can get it horizontal, with the tube lower down, and then bend it back up so it's shooting out the side. Basically, hide it in a custom cake stand, so it's actually below the cake, so the cake's still edible. But if the whipped cream idea doesn't pan out, I've already got a friend who's a pipefitter who said he can get me a Gallo gun if I just want to make a real mess of things ... but then it's a single shot, and might not be fit for consumption. –  Joe Jan 10 '11 at 4:43
    
Ah, I see @Joe. I'll try dispensing mine sideways when I have a few minutes and see what happens. I suspect that some might come out but it wouldn't be very "forceful". And, actually, I meant to mention in my answer that even when dispensing down, you really can't try to dispense too fast, otherwise the gas will just blow straight through the cream and you'll get nothing. These things just are not designed to propel. –  Aaronut Jan 10 '11 at 4:47

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