Sometimes I make whipped cream in my ISI cream whipper and it comes out beautifully fluffy and smooth, and other times when I dispense it, the cream looks "ragged" for lack of a better description. Any ideas what factor accounts for the difference?
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.
(1) You are definitely over whipping the cream. Please read the instructions - these are tested in the iSi lab to ensure your best results.And they do give you the correct amount of shakes per the fat content of the cream. You describe what we call "choppy" cream.
(2) Hold the whipper upside down in your hands. This means that your little finger is on the lever - not your index finger. This can position is very important because you need to have the gas behind the cream when it's dispensed. this will ensure that the gas is working with gravity and going through the cream and will result in less sputtering, and a full dispensing of your cream.
(3) Make sure you are using iSi branded chargers. Not all chargers are the same, and while the less expensive chargers will fit onto the charging mechanism, it can damage the pin of your iSi whipper and will VOID your warranty. The off brand chargers will provide an inconsistent amount of gas in use, and contain a high amount of oils from manufacturing that will be injected into your foods, this can change the recipe outcome.
(4) Carefully measure your contents, and don't over fill; The head room is very important for the best use of the mixing between the cream and the n20 gas. There is a pour line indicated; make sure your liquid + solid ingredients do not exceed that level (10-x sugar and cream)
I was taught how to whip cream with a handheld mixer and there are a few things to consider
Is the whipped cream being over whipped? When you beat it too hard with a handheld it starts to form ragged peaks
Is the cannister almost empty? Gas charged cannisters often 'sputter' a little bit when over-charged or almost empty.