What is a pastry bag?
Quite simply, it's a kind of large cone-shaped plastic bag (the pouch), in the bottom of which we place an outlet, usually made of very hard plastic, polycarbonate (the socket).
The bag is filled with the chosen preparation - cream, paste, mousse, etc. - then closed, and the contents squeezed out through the nozzle.
This gives you complete control over the output (flow) and shape of the cream/paste, thanks to the nozzle.
It's the favorite, indispensable tool of pastry chefs, who use it time and time again. In fact, they use the term "pocher", which in this context doesn't mean cooking, but dressing with a pastry bag.
In fact, bakers love to gently mock pastry chefs by saying that they "can't do anything without a pastry bag".
Useful at home?
Oh yes, indispensable even for an incredible number of preparations of all kinds. It's virtually impossible, for example, to make anything aesthetically pleasing in choux pastry without "poaching".
Difficult?
It's hardly complicated in principle, you just press on the bag and the mixture comes out, after which it's much harder to control the effort and precision of the gesture, but that comes with time.
Poaching regular macaroons, for example, is not at all easy, especially at first.
The first difficulty is filling the pouch, which sounds a bit odd when you say it like that, but if you're alone in the kitchen, it can quickly become a real pain: you have to spread the pouch, pour in the cream (sometimes in several stages), push it to the bottom, scrape out the rest, be careful that what's in the pouch starts to come out through the nozzle when the filling isn't finished, close the pouch, avoid air bubbles and leaks, and that's where the 3 or 4 arms I mentioned almost come into their own...
How do you do it?
1) If your preparation is rather liquid, such as mousse, cream, etc., pinch the tip of the bag with a frozen food clip, a large clothespin or even a rubber band to prevent leakage during filling.
2) Place the empty, pinched pouch in a container with a high rim (like a graduated liter), spread the edges apart and place in front of you.
3) Slowly pour the mixture into the bag, then scrape it all down with a maryse (no spillage).
4) Close the pouch by twisting the plastic (to avoid air bubbles) and remove it from the high-sided container. You can leave it to stand for a while, so your preparation is protected from the air.
5) When you're ready to poach, place the pouch with the tip upwards, remove the tongs, turn downwards and poach!
That's it, you know it all, but I'd like to finish by pointing out that, at first, it can be a bit disastrous, as you have very little control over the flow of the pouch and the shaping, but don't lose hope, you'll see with time and experience, it'll come...
To
sum up: to fill a pouch properly, pinch the end if the preparation is rather liquid, then fill with the pouch placed in a high-sided container, not held in the hand.