Food chemistry is one of my favorite topics to discuss, especially when combined with actual food :-)! That’s why this month is food chemistry month. Caramelization is one of the most fascinating food chemistry reaction, so let’s have a look at it while making honeycomb!
Honeycomb is a great, very simply sweet treat to make. It’s a crunchy, snappy, airy sugar structure with a nice honey like colour. Just like real honeycomb ;-)!
I think making honeycomb is nothing more than performing a chemistry experiment, with the appealing results of making something that you can actually eat! You are actually initiating at least two chemical reactions: caramelization & an acid base reaction which causes leavening. We already discussed the leavening part earlier this month. So, let’s focus on caramelization in this post, but not before I share the recipe!
- 100g sugar
- 45g corn syrup
- ½ tsp baking soda
- Mix the sugar and corn syrup in a pan and add a small layer of water (the exact amount doesn't really matter, if you add more you will simply be cooking longer to boil it all off again).
- Boil the mixture to a temperature of 150C (using a thermometer really is the best way).
- Take the mixture of the heat and mix in all the baking soda in one go. Do this fast and watch out, the very hot(!) sugar syrup will start bubbling a lot.
- Immediately pour onto a heat resitant surface (I use a baking tray covered with baking paper) and leave to cool.
- Once it's cooled down it should break into shards easily.
Sugar candy & a candy thermometer
Sugar is very fascinating when heated together with water. Since this post is on caramelization I will not go into too much detail, but I cannot resist discussing at least a little snippet… I’ll surely come back later to it with a lot more thermodynamics :-)!
My candy thermometer is my best friend when making sugar candies, so also when making honeycomb. This has to do with what happens when a sugar solution is heated up. Let’s start at the beginning.
When making most sugar candies you will start with a lot of sugar and some water (just like I did for my honeycomb). Generally you won’t be able to dissolve all the sugar in the water. By heating up the water you will be able to dissolve more sugar (all of my sugar had dissolved once the water was boiling). Pure thermodynamics. Once your sugar solution is boiling, water will be transforming into a gas (that’s what happens when you are at the boiling point). However, by evaporating water, the concentration of sugar will increase. Interestingly, the boiling point of a sugar solution depends on the sugar concentration. Therefore, the more water evaporates, the higher the temperature is required to keep it boiling. So, the temperature goes up.
This will go on until you reach the caramelization temperature, at this point the water content is very low and if you keep on heating the sugar will burn.
In the basics, boiling such a sugar solution is not very special, the interesting thing is what happens when the sugar solution cools down again. By bringing a sugar solution to a very specific temperature, you have also made a solution with a very specific water content. When cooling this down, the water content will remain the same.
This is where the scales on you thermometer come into play! See the red areas on my thermometer? The T stands for thread, so this solution will form a thread when cooled down. The H stands for hard ball stage, yes, this will form a hard ball when cooled down. For honeycomb I want to make a snappy, cracky, brittle product. To get this you will have to heat a sugar syrup to at least 150C. When making my honeycomb I indeed tried to get to the 150C (although I didn’t always succeed…).
Just in case your wondering why these stages have such interesting names, this is because when you don’t have a thermometer you can drop some of your sugar solution in ice water. By seeing how this bit of sugar syrup has transformed, you will know whether you have reached the correct temperature!
The initial ingredients of honeycomb (corn syrup and sugar) are both pretty transparent, neverthless, honeycomb will have a nice golden colour. That’s all thanks to caramelization.
Caramelization is what happens when sugars are heated to such a high temperature that they start decomposing, breaking apart. A whole rang of chemical reactions takes place as a result of this forming brown (and if you heat too much, black) colours and a range of aromas. The temperature at which caramelization starts depends on various factors. The first is the type of sugar. Regular sugar (sucrose) and glucose start caramelizing at 160°C. Other sugars might start at lower or higher temperature.
In my honeycomb I’ve used corn syrup. Corn syrup contains a lot of maltose, also a sugar. This sugar only starts caramelizing at 180°C. So it’s even harder to brown.
As I wrote in the previous paragraph, honeycomb should be heated to 150°C to get a nice brittle texture. However, you might now realize that this is still below the caramelization temperature, which is correct. However, there are other ways to speed up caramelization. One way is the modify the amount of acids or base present. As you’ve learned in my special on baking soda, baking soda can react as a base. Adding baking soda to something will make it more alkaline (or less acidic). By making it less acidic and clearly more alkaline, the caramelization will be sped up quite a bit! Once I added baking soda to my honeycomb the colour clearly darkened to a perefect golden honey colour.
The great thing about baking soda is also that it gives a lift to your product! The baking soda will form gas (see my other post on the topic) and create air bubbles in the sugar syrup. This is great because a solid sugar solution that’s been heated to this temperature will be very hard and tough to eat. But because of all the air bubbles it brakes easily and eating is no problem at all!
Last but not least, if you don’t use a pure sugar but a mixture (as is the case for corn syrup), impurities can also speed up the reaction. My honeycomb started turning a light brown at 150C, even before I added any baking powder.
Chemistry of caramelization
I’ve gone into too many details already for this post, so I will restrain myself and not dive into the hard core chemistry of caramelization. I’ll save that for another time and keep with the basics. To start with, food chemists still aren’t very sure what exactly happens during caramelization. They know which types of reactions take place, however, there are so many reactions which all take place at the same time that it’s very hard to know about all reactions!
In its essence sugar molecules will lose water molecules which in turn allows them to react into a whole range of coloured molecules, often with a strong aroma as well. Several mechanisms have been found, but the overall formation of brown components is more complex.
Why does baking soda work?
Ok, if you’re like me, you are asking yourselves a question now. I just learned that baking soda can form a gas (carbon dioxide) by reacting with an acid. However, we don’t add any acid to the honeycomb, why does it still work?! Great question, I like your thinking. I haven’t (yet) been able to find a conclusive answer. But here’s what I think happens.
First of all, baking soda (sodium bicarbonate) is not a very stable compound, it can react pretty easily for form a gas. When the temperatures are so very high (as is the case with honeycomb) this reaction might can ahead without the acid, it’s probably more stable for the component to be a gas any way. Second, at these high temperatures sugar starts decomposing slightly before caramelisation occurs and impurities will be present from the corn syrup. I think that at least some acidity will be present which will help catalyze the reaction even further.
Interested in learning more about honeycomb? The guardian wrote a great article about honeycomb, with a lot of in depth details. The recipe I used is inspired by theirs. There are also a lot of scientific articles written about caramelisation and the like, for those interested, have look here and here.