This year, the week before Halloween, I was stricken with the ghastly Fall sickness. Perhaps I’m being dramatic - really it was just a cold, but it kept me home on the couch for a day catching up on my Bon Appetit magazines AND watching all of Halloween Baking Championship. I had already planned to be making a Halloween-themed birthday cake later in the week (for a really great kid, who specifically requested chocolate & vanilla cake with strawberry frosting), but after my four-hour sugar gore tv binge, I couldn’t help but bloody it up a little. Time to make sugar glass!
Sugar glass is...
…everywhere! In the movie and theatre industry a lot of the glass sheets and bottles you see people breaking are actually made of sugar, because it’s easy to form into specific shapes (with molds), inexpensive, breaks easily, and is much less dangerous.
…essentially just a lollipop. When you cook sugar (typically with some amount of water), as the water evaporates and the temperature rises, it goes through different “stages”. The Soft-Ball Stage (235° F–240° F, sugar concentration: 85%) is named as such because when you take a drop of the sugar and submerge it in a bowl of ice water to rapidly cool it, it will turn into a soft ball of sugar and will flatten easily between your fingers. This temperature is what you’d use to make fudge, Italian meringue, and fondant icing (not rolled fondant - two different things). The Firm-Ball Stage (245° F–250° F, sugar concentration: 87%) is used for caramel candies. The Hard-Ball Stage (250° F–265° F, sugar concentration: 92%) is used for marshmallows (!!), nougat, and rock candy, while The Soft-Crack Stage (270° F–290° F, sugar concentration: 95%) is used for taffy and candy apples. And finally, The Hard-Crack Stage (300° F–310° F, Sugar concentration: 99%) is what you hit for toffee, brittle, lollipops and…you guessed it - Sugar Glass! (To read more details about cooking sugar, and about what happens if you keep going, visit the exploratorium.)
…really easy! You need only seven items in total - four ingredients and three tools. Oh, and attention and patience. Those two are equally as important.
Ready? Happy Baking!
Light corn syrup
Cream of tartar (optional, but it will help prevent crystallization and will keep your “glass” clearer)
(see Directions below for amounts of each)
Candy thermometer (not optional! This one is my favorite.)
Cooking spray, shortening, or coconut oil
Half sheet pan with edges
You can make sugar glass in any amount, with the ratios of 1-2-3.5 cups for the corn syrup, water, and sugar respectively. In those ratios you’d use 1/4 teaspoon of cream of tartar, so you can adjust that measurement accordingly. For mine I knew I didn’t need very much, so I cut those in half, using 1/2 cup corn syrup, 1 cup water, and 1.75 cups sugar, and 1/8tsp cream of tartar. This filled about 3/4 of a half sheet pan. If you use a half sheet pan with twice that amount, your glass will be thicker. In the picture of the cake above, I used probably about 1/10th of the amount of glass I actually made.
Add all your ingredients to a saucepan and whisk together until fully combined, taking care to not get a lot of sugar granules up along the sides of the pan.
Place over medium-high heat and stir gently frequently until it just starts to bubble - then STOP STIRRING!
Attach your candy thermometer so you can cook the mixture to 300° F - this could take quite a while. I was using an induction burner (typically 1/3 to twice as fast as gas heat) and it took me about 20 minutes, so don’t be surprised if it takes you 40, but don’t walk away either! The great thing about the thermometer I recommend above is it has an alert setting where it will start to beep once it reaches a certain temperature of your choosing. So, you could set it to 280° F, and go do something else within earshot, and come back to watch the rest of the creep to 300° F once it beeps.
As soon as you leave it alone to bubble and boil, prepare your sheet pan by spraying it well with cooking spray, or greasing it with shortening or coconut oil. Take a paper towel and smooth out your grease so there aren’t any pools, but try not to take too much away. If you don’t coat it fully it will be difficult to near impossible to pry up your hardened sugar.
Have your sheet pan close by on a cooling rack, and throw on some pot holder gloves. As soon as your sugar reaches 300° F, pour it quickly but gently into your sheet pan and immediately start tilting the sheet pan to difference sides so the sugar spreads itself as easily as possible. This won’t take too long because if your sugar doesn’t fill your pan, it will eventually pick up enough of the grease that it will just sort of slide around without continuing to spread out - at that point, put it down and walk away!
I set my pan outside on my porch to cool, and it was hardened and ready to go in about 15 minutes in 40 degree weather. If you keep it inside it’s possible it could take an hour or so. Don’t try to remove it from the pan until it’s really solid and both the top and the bottom of the pan are completely cool to the touch.
Pry up an edge with a thin knife, and it should start to break by itself - check out the picture below to see how my glass initially broke, all on its own! Then lay the sheet(s) on paper towels on a large table, and hit it as many times as you want in different places, just hard enough to crack it with the end of a chef’s knife.
Oh, and here's a video of sugar boiling in slow-motion, cause it's freakin cool: