The easiest way to get an ingredient onto the conveyor is to switch it with a candy to its left or right, if the two candies below it are the same colour as the one you switch it with.
You can also drop down the ingredients onto the conveyor by matching the candies below them or by using a Colour Bomb to remove the candies underneath them.
Pay attention that there are STUCK ZONES, so try to not make matches below the conveyor, when the ingredients are in the columns 2 or 8.
You can win this level without destroying the popcorns, but it's better to remove them. Colour Bombs can be useful to get ingredients onto the conveyor, as said above, and without them you have more chances to make special candies in the middle of the board.
The maximum number of ingredients on the board is 2, the third will spawn when one of the first two is collected.
There are no candies below the Ingredients cannons, so if you drop down an ingredient or two and no matches are made under the dispensers in the same move, the ingredients will spawn from another point of the board (see video below 2:26). This is probably a bug, but why not milk it while it's there.