Decorating bags are simply pastry bags that are filled with icing. However you should not use bags that have been filled with batter as grease can cause your icing to become lumpy and affect the pressure of the flow of icing out through the bag. There are three types of bags: Featherweight, Disposable, and Parchment.
These bags can be used with or without a coupler. To use without a coupler, cut about 3/4 in. off tip of Disposable Bag (Featherweight Bag is ready to use). Simply drop the decorating tip you want into the bag with the narrow end of the tip down.
A new Featherweight bag will have to be trimmed with scissors to accommodate the coupler base. First, twist the ring off the coupler base. Drop the coupler base, narrow end first, into the bag and push as far down as you can.
With a pen or pencil, mark the spot on the outside where the bottom thread is outlined against the bag material. Push the coupler back up into the bag, and cut across where you have made the mark. Push the coupler base back down through the bag opening. One thread should be showing.
Choose the decorating tip you want to use and slip it onto the coupler base. Now twist the coupler ring over the tip, locking it in place. Changing decorating tips is easy: Twist off the ring, replace with new tip, then screw the ring back on.
Disposable Bags are made of clear plastic. You simply throw them away when you are done. Parchment Bags are made from envelopes created by parchment paper triangles. Generally, you’ll use parchment bags to make decorative highlights with small amounts of icing, then discard each bag when it’s empty.
The coupler is a two-part device that screws on to the icing bag. This allows you to change the decorating tip without changing the bag.
The two parts of the coupler are the base and the ring. The base fits inside the bag, and then you put the decorating tip of your choice over the portion of the coupler that sticks out of the bag. When you screw the ring on, you’ve locked the decorating tip onto the coupler and bag.
When using disposable bags note that notice that the threads in the coupler base start about 1/2 in. above the tip. Push the coupler base into the bag as far down as possible. With scissors, trim bag about 1/4 in. below bottom edge of coupler. Position decorating tip over coupler base and bag. Screw ring in place to secure. To change decorating tips, unscrew ring, replace decorating tip and screw on ring.
The most important thing to remember is not to overfill the bag, or icing may squeeze out the wrong end. The right amount of icing to start with is about 1/2 cup.
Fold down the top to form a generous cuff, and hold the bag beneath the cuff. Use your spatula to fill the bag with approximately three tablespoons of icing at a time.
To remove icing from the spatula, hold the bag on the outside between the thumb and fingers. Then pull the spatula out of the bag, using the bag and your fingers to squeeze the icing off.
To close the bag, twist the icing bag tightly closed, forcing the icing down into the bag. You can make sure you’ve released any air trapped in the bag by squeezing some of the icing out of tip into the bowl. This is called “burping” the bag.
You are now ready to make whatever designs you need to for your cake.