Toffee with Gas

by mutteringhousewife

You’re getting a peek today into one of my tutorials.  I’m teaching fledgling primary school teachers how to teach science and every week we do some hands on activities around one topic.  This week we’re playing with air, and there was an activity planned which involved gelatin and a blender and various other things to make something edible with air whipped into it.  Well, you know how it is with blenders.  These were cheap and nasty ones and burned out on Monday.  We can’t have the students not knowing anything at all about air in food.  So I’m going to tell them about one of my favourite combinations, air and sugar.

But first!  Just the sugar.  For a control I need to make this food without the air.  When you heat up sugar dissolved in water quite a lot and then cool it quickly, what do you get?  Does anyone know?  That’s right, toffee, a gold star for you.  Just doing it with white sugar is a little dull, so here’s the recipe I’m using today.

Place in a large saucepan three quarters of a cup of white sugar, two tablespoons of honey, two tablespoons of golden syrup and two tablespoons of water.


Generally a toffee mix will have more water in it, but bear with me.  Heat it gently while stirring until the sugar dissolves.



Not too gently, you don’t want to be there all day.  You let that bubble away without stirring it until it gets to about 150 degrees Celsius.  You determine what the temperature is with a candy thermometer.



If you have a dodgy thermometer like I do that appears to have got water in it and is unreadable, or just don’t have one, you want to test the mix periodically for consistency.  You do this by dropping a bit of it onto a saucer of cold water.



Those little blobs will go from stuff you can swirl around, to blobs that retain their shape, to blobs that are fairly firm but can be squished, to hard crunchy little blobs.  Those last two steps can be quite close together.  Get that stuff off the heat and pour it onto a baking tray lined with baking paper.


Pretty soon it will harden and you can snap it into bite sized tooth gluing pieces.



We could go into the chemistry of what’s going on here, and it’s a lot more complicated than you’d think.  I’ll restrain myself and just mention that the sugar hasn’t really melted, kind of, because it’s thought that sugar doesn’t actually melt, it decomposes into a whole lot of other compounds, some of which melt at this temperature and some of which don’t, and it’s still kind of in solution with a tiny bit of water.  Dumping it onto a cold tray not only recrystallises the sugar and the breakdown compounds, but by doing it fast you’ve also turned it into a glass.  Don’t get me started.

So how do we add air to toffee?  I’m glad you asked.  Bicarbonate of soda.

Make the toffee as before.  But just at that point where you’re taking it off the heat, chuck in a teaspoon and a half of bicarbonate of soda.  You’d kind of expect that a bit of bicarb into this super hot boiling mess would pretty much explode.  But it doesn’t, because what it would like to react with is water, and there’s only a tiny bit in there.  Mix it fast with a wooden spoon, you want those carbon dioxide bubbles distributed throughout the whole lot before it starts solidifying.  Dump it, as before, onto a lined baking tray.



Honeycomb.  You’ve made honeycomb.  It has little to no resemblance to that waxy stuff you find in a beehive, but we’ll let that go too.  This will also set pretty fast, when it’s cool you can snap it into pieces.  Now taste some of the toffee and some of the honeycomb.  The honeycomb will give you a bit of a buzz on your tongue from unreacted bicarb, but ignoring that, aren’t they completely different eating experiences?  And the difference is air.  You lucky lucky tutorial class, you actually get to try some.  Aren’t you glad the blenders burned out?