While ganache is often used as truffle centers or to glaze cakes, it can also be used for piping decorations. Creating ganache roses requires attention to the consistency of the chocolate and your piping technique. Once you decide which style of ganache you are most comfortable working with, a bit of practice is all that's required to produce beautiful roses. After creating them, you can place them on a cake glazed with ganache for a striking chocolate-on-chocolate look.
The Right Ratio
The ganache used to glaze cakes often requires a one-to-one ratio of chocolate to heavy cream. If you desire to make roses out of leftover ganache from frosting the cake, you need to cool the chocolate to a much stiffer consistency. Either cover the ganache with plastic wrap and place in your refrigerator to chill or cool it down by placing the bowl in an ice bath, making sure not to allow water to touch the chocolate. Alternatively, for stiffer flowers that set up more firmly, make a new batch of ganache with a two-to-one ratio of chocolate to heavy cream. Allow the mixture to cool to room temperature before piping the roses.
Whip It Well
Whipping the ganache before piping results in a consistency similar to an American buttercream. Once your ganache has cooled and resembles pudding, place it in your mixer and whip it with the wire whisk until it reaches the consistency of frosting. Typically, this takes 30 to 60 seconds. If you over-whip the ganache, it separates and hardens, similar to the way whipping cream turns to butter with too much mixing. Once the ganache whips to this stage, there is no saving it, and you have to start a new batch to get the right consistency for roses.
Keep It Cool
Regardless of which style of ganache you use for piping roses, keeping the chocolate the correct temperature is key. If the ganache gets too cold, you will be unable to pipe the petals. But if it gets too warm, the chocolate will not hold its shape. Once your ganache is at the correct consistency, work quickly to avoid significant temperature changes. The warmth from your hands on the piping bag may cause the ganache to begin melting along the edges. If this happens, place the filled piping bag inside the refrigerator for a minute or two to cool it down.
Tips and Tricks
Affix a small square of parchment paper to the top of your rose nail with a bit of ganache, then pipe your rose as you normally would. Slide the rose off of the nail by pulling the parchment across it and place it on a plate or cardboard cake base in the refrigerator. This allows you to make a number of ganache roses and keep them cool until you are ready to position them on your cake. Once you've completed your ganache roses, keep them out of sunlight and heat to avoid altering the color of the chocolate; otherwise, you may end up with splotchy flowers. Allow any extra ganache roses to set up in the refrigerator, then cover them with plastic wrap and store for up to a week.