Foamed candy: Sponge toffee
February 28, 2011 
2 Comments
It always irks me when people make the sweeping declaration that “foams” are a fad that will soon fade. While this may be true of some types of foams – although even there, I’m not convinced – foam is a structure that cuts across all categories of food, savoury and sweet.
Take, for example, the latest foam I made. Does it really seem like a passing fad? The Crunchie bar was introduced in 1929 and is still available today, after all.
There are a couple of aspects of sponge toffee that make it interesting as a foam. For one thing, it’s a solid foam, unlike the other foams I’ve written about previously, which were liquids. There are two easy ways to make solid foams. You can make a liquid foam, then drive the water out of it, through baking (as in bread) or dehydrating (as in certain types of meringue). Alternatively, you can use a base that’s solid at room temperature, heat it up and add the bubbles, then cool it down again, trapping the air. Chocolate and sugar are frequently used in this way.
The other thing that makes sponge toffee interesting as a foam is that the gas isn’t dissolved or whipped in, but produced through a chemical reaction: the sugar syrup is heated with acidic corn syrup and honey, then baking soda is whisked in, producing a multitude of carbon dioxide bubbles. In this respect, it’s very similar to quick breads, which use an acid-base reaction (usually in the form of baking powder) for their foam structure.
I find sponge toffee to be compelling because it’s the foaming action that makes all the difference: if you were to just heat sugar syrup to the hard crack stage and pour it into a pan, you’d break your teeth trying to eat it! But turn it into a foam, and it immediately becomes a treat to be savoured. I’m hoping to be able to dip this batch of sponge toffee in chocolate, but I fear it may not last long enough.
That looks perfect. I got that result a few times, but many many more have been either too bitterly tan in the center, or didn’t lift enough and was too hard and dense.
Thanks, sammy. You certainly have to be careful with the caramelizing, and work quickly once the baking soda has been added! I’ve heard that warming the pan in advance, and keeping it warm as the candy cools can help with the lift.