What is sugar crystallization?
You may have heard about sugar crystallization or experienced it for yourself. Have you ever had a jar of golden, syrupy honey turn into a solid, grainy mess? Have you ever made some simple syrup for your cake and discovered a few days later that it looked more like toothpaste than syrup? That’s crystallization.
You might be wondering what went wrong or if you need to adjust your recipe. Crystallization is a chain reaction where the melted sugar starts to re-form into its crystalline (grainy) state. It’s easy to start this chain reaction, even if you are using a great recipe and are being careful with your techniques. You might make a recipe dozens of times and find that sometimes crystallization occurs and sometimes it doesn’t.
Sugar crystallization has been plaguing candy makers for years. Sometimes crystallization will ruin your final product, but other times it’s not a problem, or it may even be part of the recipe. Fortunately, we do know what causes crystallization and how to prevent it, but it can be hard to adhere perfectly to these techniques. Still, there is a lot that can be done.
What does sugar crystallization look like?
Crystallized sugar looks grainy, solid, and opaque.
The sugar mixture in the top photo was originally a thick, orange-flavoured syrup that was left over from making candied orange peel. I left it in my refrigerator for a couple of days and it went solid and grainy – I won’t be pouring it on my pancakes!
The middle photo shows some candied orange peel. It still tastes fine and can be used in recipes, but it doesn’t look quite as pretty as smooth-edged, shiny orange peel candy. If I’m going to chop it up for fruitcake, I won’t even notice the crystallization. If I want to dip it in chocolate and serve it as candy, well … I’d eat it anyway, who am I kidding, but it wouldn’t look as good.
Sometimes crystallization is the key to a recipe. Rolled fondant (the type you see on the outside of cakes) is a sugar syrup that is poured on to a slab and stirred with a spatula until the sugar crystallizes and forms a soft, opaque and stretchy white candy. The bottom photo shows a tiered cake with a layer of fondant, a confection that has been crystallized on purpose.
How can I prevent crystallization?
There are two approaches to preventing crystallization. The first approach is to avoid doing anything that causes crystallization. The other approach is to add something to your recipe that gets in the way of the crystallization reaction. These additives are called interfering agents.
Stray grains of undissolved sugar can start the crystallization reaction, since they are already in the crystalline state and put a lot of peer pressure on the rest of the sugar, since crystallizing is the cool thing to do. You can also trigger crystallization by shocking the mixture – too much stirring or even a cold utensil can trigger the crystallization reaction.
To prevent crystallization, use the following techniques:
- Wash down the sides of your pan with a wet pastry brush. Once the sugar has dissolved, take a wet pastry brush and brush down the sides of your pan with water. Make sure that there are no undissolved grains of sugar that stick to the side of the pan, since their presence can trigger crystallization. (Some people keep the lid on the boiling mixture so that the steam trickles down the side and does the same thing.)
- Avoid stirring the mixture. You’ll need to stir the mixture while the sugar dissolves, but try to avoid stirring after that. If you need to mix your ingredients around, try swirling the pan instead.
- Warm spoons and candy thermometers before inserting them in to the mixture. Cold utensils can shock the mixture into crystallization, so warm them up before you insert them. You might want to consider using a laser candy thermometer, which does not need to be inserted into the liquid at all.
To combat crystallization, use an interfering agent:
- Corn syrup contains sugars that discourage crystallization. (Note that the corn syrup you buy in the grocery store is not the same thing as the controversial high-fructose corn syrup food additive).
- Cream of tartar and lemon juice are acids that help block the crystallization reaction.
- Other ingredients in the recipe may also interfere with crystallization, for example milk and cream.
How can I fix sugar that has crystallized?
You can fix crystallized sugar by remelting the sugar crystals and trying again. You may want to add an interfering agent, and of course you want to be careful not to trigger the crystallization reaction. This is easy for crystallized liquids – simply reheat the crystallized syrup and try again. Other confections may or may not be easy to fix, depending on the recipe. You might just have to live with it! (But don’t worry, crystallization doesn’t ruin the taste, it just messes up the texture.)
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Examples of crystallized sugar. Top: crystallized syrup. Middle: crystallized orange rind candy. Bottom: Rolled fondant, which has been crystallized on purpose.