Goat Cheese is dry compared to many other cheeses. We make a goat cheese pizza but have to moisten the shredded goat cheese with goat milk into a kind of slurry. Very low in lactose and tastes good but it doesnt even melt much because it is so dry. Probably lower in fat too I would guess. If your espuma is too dry try adding more goat milk to the mixture until it just moves in the blender.
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.
Best Answer
When I first got my iSi I had wildly inconsistent results, including exactly what you're describing. I'm not sure if you're just whipping cream or if you're whipping other cream-based preparations, but the most common reason for this happening is that the liquid going in isn't quite, er, liquid. Any solid particles of any kind will almost assuredly cause sputtering, which is why they recommend that you strain everything through a fine sieve.
Other things I've learned about the iSi whippers to help prevent these inconsistent results:
Ignore everything the instructions tell you about how to charge it. They're somewhere between very misleading and complete nonsense. What I actually do is this:
Screw on a charger as described.
Shake it vigorously, as if it were a cocktail shaker.
Let it rest for a moment, then shake again. Repeat the shaking 4-5 times.
Finally, remove the charger and screw the cap back on.
The instructions are full of ominous warnings about not being able to discharge it properly if you shake it too much because the nozzle will get blocked or something. Never happened. What's far more likely is that the cream doesn't actually whip fully or there are large air pockets. Do not err on the side of caution here; many "external" iSi recipes such as those you find in the HRC actually tell you to shake frequently as the dispenser chills. I'm not sure if I'd do this with cream (as opposed to a water-based foam) but I can't stress this enough, don't skimp on the shaking.
If you need to chill it some more after charging, make sure to chill it on its side. The instructions are quite explicit about this and in this case they're actually correct.
Shake it again after you chill it and before you dispense any. This is very important and conspicuously absent from the instructions. You shouldn't need to shake as much as the first pass, but some of the gas does seem to separate over time.
Start by dispensing the cream very, very slowly, until you actually see some come out, then you can apply more pressure as needed. If you squeeze the trigger as hard as you can right off the bat, you'll just end up depressurizing the thing before any cream has a chance to come out. Every single time I've pulled too hard, I've ended up with spatters.
Finally, make sure that you actually thoroughly clean it all between uses, including the tiny horizontal hole in the metal tube that you screw the tips onto (I forget what it's called) as well as the socket that piece goes into. Any blockages whatsoever, no matter how small, can cause at least minor sputtering.
Hope some of that helps. If you do all of that, you shouldn't have any sputtering issues. Last 7 or 8 times I've used mine, I haven't had any.