Hard Candy Chemistry!

So I'm Rich Hartel. I'm a professor and faculty member here at the University of Wisconsin. I teach candy science. So we're going to make some heart candy today. This is a mixture of granulated sugar. You can see the white stuff here. We have corn syrup in here as well and then we have water to help dissolve the sugar. We're just going to dissolve all the sugar and make sure that there are no sugar crystals in here because eventually we're going to make heart candy which is a sugar glass so we don't want crystals. So we've reached the boiling point now and so essentially we're going to follow the boiling point elevation curve up. So I'm making heart candy. We're going to boil up to what's called the hard crack stage where temperatures are on the order of 300 degrees Fahrenheit and water contents are down around two or three percent. So we're now at the 233 degrees Fahrenheit range and this is where we have the thread state and what that means is the viscosity is high enough that when you pour this into cold water it forms threads as it falls through there but the viscosity is still low enough that those threads dissolve fairly quickly. So we're now at about 240 degrees and this is according to the candy thermometer where we find the firm ball state and so we boiled enough water that when you pour this into when you drop it into cold water it forms a coherent mass that you can take out and form it into a ball that can still be manipulated so it's plastic enough to be malleable but it's still a firm ball that can hold its shape. Okay and we're at about 298 now and so I'm going to stop it and take it off the heat. So we're now going to take this over to the cold table and pour it out and start the next stage of the process. So at this point we've poured it onto the cold table and it's starting to cool. You can see that as it cools it becomes more plastic, more firm. We have some color granules and we'll add those in here. Some flavor so we're going to add a little bit of lemon flavoring to this and then we're going to add a little bit of acid as well. So right now we're in the stage where it's becoming a plastic mass and we're just trying to get it into a shape that it will go through the rollers. It still has enough heat in it and viscosity is low enough that it starts to flow. So if I were to form it now it would form but then it would quickly deform just like it's doing here. So this is just about at the point where where we can form it. It's viscous enough that it's not flowing very quickly yet it's still plastic enough that we're going to be able to get it through the rollers and turn it into a nice candy. So as you can see we're sending this plastic mass through these drop rollers. They fill into the shapes and make the drop shaped candy. So now our lemon drops have solidified enough. They've reached room temperature. We're now there in the form of a sugar glass. So this is just like window glass except it's made of sugar molecules not of silica. But now because it's in a sugar glass I can drop this onto the tray and it's going to shatter. It'll shatter along the webbing here leaving behind some intact lemon drops. So at this point we have lemon drops but they have all these sharp edges on them still. So the next step in the process would be to put them into some kind of tumbling drum to smooth out the edges.