quite dense honeycomb

The Science of Honeycomb Candy (+ Troubleshooting Tips)

Honeycomb definitely is one of the more theatrical candies to make. Once you add that baking soda to the boiling hot sugar, the fizzing and puffing are sure to impress your viewers. Once the show is over and your honeycomb has cooled down, you’re left with a light and airy, super crunchy candy.

It’s pure chemistry at work and a surprisingly interesting balancing act, considering you need only 3 ingredients and two process steps to make it. Get your sugar types and ratios wrong and the honeycomb collapses or turns sticky. Use too much or too little baking soda and the light and airy puff collapses on you or doesn’t even materialize.

Luckily, we’ve got chemistry and science to help us out here and problem solve the art of making honeycomb.

What is honeycomb candy?

Honeycomb candy (also called cinder toffee, seafoam, sponge toffee, or one of many other variations) is a simple, sugar-based, airy, and very crunchy candy. It is closely related to toffees or brittles. The main difference though is that it contains a lot of smaller and larger air bubbles. Without these bubbles, the honeycomb would be very hard and tough to eat. These bubbles are also what give the honeycomb its name! It kind of looks like a ‘real’ honeycomb.

Making honeycomb requires only three ingredients: sugar, sugar syrup (e.g. corn syrup) and baking soda (more on those later). You bring the sugars to the boil and once you reach the desired temperature (which is well above the boiling point of water!) you add baking soda. This baking soda fizzes and expands the sugary liquid into an airy mass. Simply leave it to cool and it will set into a hard, crunchy but light texture.

Honeycomb doesn’t get its name from the fact that it’s made with honey (even though you can make it with honey). Instead, the light and airy shape will remind you of a ‘real’ honeycomb!

What happens when you make honeycomb?

Making honeycomb truly is a great science experiment. During each of the phases of making honeycomb, cooking, expanding & cooling, a core scientific process is taking place. So let’s have a look at each of these.

Step 1: Cooking Sugars

Making honeycomb starts out by cooking a mix of sugars (more on those later) to a very high temperature. This sugar solution is made out of a mix of different sugars such as sucrose, glucose, fructose as well as other larger carbohydrates and water.

cooked sugars
Sugars cooked to 150°C, this version was made with honey, hence the light brown color
Concentrating Sugars

When you start boiling the sugars in water you are dissolving all those sugars in the water. The white sugar crystals will disappear as they dissolve in water. Once all the sugar is dissolved and you continue heating the solution, you’ll be boiling off water. You’re concentrating the sugar by evaporating water from the sugar solution.

Pure water boils at 100°C (212°F, assuming you’re at sea level). Because of a phenomenon called ‘boiling-point elevation’, this boiling point increases with an increasing concentration of sugar. By evaporating water, you’re increasing the sugar concentration and thus increasing the boiling point. It is why the temperature of your sugar solution goes up and up and when you continue to boil it.

Similar to the “boiling-point elevation” adding sugar to water can also decrease the freezing point, this is called “freezing point depression” and is used to make smooth and soft ice cream!

The temperature of the sugar solution and the concentration of sugar in that solution are very closely correlated. As such, once a sugar solution has reached a certain temperature, you will know it will have achieved a set concentration. Just how high the concentration of sugar is in your sugar solution will impact how that sugar behaves once it’s cooled down again! We discuss this in far greater detail in a post focused on those ‘sugar cooking stages‘.

Aiming for a glassy structure

If you concentrate that sugar solution enough there is so much sugar in the water, that once you cool it down again, those sugar molecules cannot move around freely anymore. Instead, they will form a ‘glass’. This is a hard, brittle, but smooth, texture. The candy called ‘brittle’ is such as glass, as is toffee. It is also what you’re after when making honeycomb. You want the sugar to be so concentrated that upon cooling it forms a stable glassy structure.

This is why instructions for making honeycomb will often mention a temperature to which you have to cook the mixture. This temperature ensures that you’ve reached a high enough concentration of sugar for the honeycomb to be brittle!

Fixing an incorrect temperature

Too High

If you’ve overshot the temperature, add a little extra water and hold off on adding the baking soda. The additional water cools down the solution and decreases the sugar concentration. Just continue boiling again and this time stop at the correct temperature.

Note: If you’ve overshot the temperature by a lot your sugars might have started to brown and caramelize. You can still use the fix, but, your honeycomb might turn out browner and more bitter.

You can’t use this fix forever. The prolonged heating will break down some of the sugars, changing the composition of the sugar solution. If you have to ‘fix’ your solution too often (more than 2-3 times) you can run a risk of the honeycomb becoming a little more sticky than you were hoping for.

Too Low

If you haven’t cooked your syrup to a high enough temperature, simply continue cooking!

However, once you’ve added your baking soda there’s no way back. What you will find though is that your honeycomb won’t be brittle and hard. Instead, it might turn out soft and maleable once it has cooled down. You haven’t evaporated enough moisture.

No significant browning just yet

Sugar will caramelize when it’s heated to high enough temperatures. During this process, the sugar turns brown and a lot of caramely flavors get formed. When cooking your syrup you might see the sugar solution starting to turn a light brown, however, it will tend to stay quite pale in color. This is ok. More color will be formed in the next step.

If you’re using a sugar syrup that has some color already (e.g. golden syrup, dark corn syrup) your sugars will have a color at this point!

Step 2: Expansion

Once you add the baking soda, the sugar syrup starts to expand!

Once you’ve cooked that sugar long enough to evaporate all necessary moisture, it’s time to expand that toffee and create the honeycomb structure! This is done by adding baking soda. Baking soda is a commonly used leavening agent in cakes, pancakes, and many more products. It works the same in those products as it does in honeycomb.

The chemical name for baking soda is sodium bicarbonate (NaHCO3). When sodium bicarbonate reacts with an acid it will react to form carbon dioxide, which is a gas. This gas is formed all throughout the honeycomb and expands the sugar solution, creating a lot of air bubbles! The higher the temperature, the faster this reaction happens. Since the sugar solution for a honeycomb is pretty hot, it all happens very quickly.

For the chemists: the reaction that takes place when baking soda reacts is: HCO3 + H+ H2CO3 –> H2O + CO2. The acid (H+) comes from the corn syrup and sugar themselves which are naturally slightly acidic. Since the temperatures are so high, only a little acid is required for the reaction to happen rapidly.

From: our post on baking powder & baking soda
Some caramelization happens as well

Caramelization of sugar is a complex series of a lot of chemical reactions all taking place at the same. Caramelization happens when pure sugar is heated up to very high temperatures (above the 150°C that you use for honeycomb). However, it is sped up when the pH is acidic or alkaline. By adding baking soda (which is alkaline) to the sugar solution you help accelerate these reactions. As a result, your honeycomb can turn a lot browner.

Color turns yellow/whitish

At the same time, your honeycomb might also turn a light yellow during expansion. In the gif above you could see that transformation. This is caused by the incorporation of air bubbles. Air bubbles reflect the light differently than a solid mass of sugar would. As a result, the honeycomb turns a lighter color!

Adding too much or too little baking soda

Getting the quantity of baking soda right is important to get the right number and size of air bubbles. If you don’t add enough baking soda the honeycomb will remain quite dense, with only small air bubbles.

quite dense honeycomb
This honeycomb was made with quite a small amount of baking soda (1/4 tsp per 150g sugar). The resulting honeycomb does have air bubbles, but they’re pretty small and not too many.

You can also add too much baking soda though! If you add too much so many air bubbles are formed that a lot of them will escape from the honeycomb before it has time to set. Also, you run the risk of not all the baking soda reacting and leaving behind a very metallic aftertaste.

Step 3: Glass formation

The last seemingly simple, but crucial, step is cooling down the honeycomb. While the honeycomb cools that glass like structure has to be formed. The liquid sugar syrup turns into a glass. This happens by itself but should happen reasonably fast to ensure that all those carefully created gas bubbles don’t get a chance to escape and get captured permanently. As such, you can’t make a huge tank full of honeycomb. It will take too long for the center to cool down, causing the gas to escape.

Only during cooling will you be able to see if you prepared the sugar syrup properly. Does the honeycomb not turn solid but remain soft? Chances are you’ve not cooked it for long enough or used the wrong type of sugars (more on that later).

Mould to pour it into

The honeycomb will be very bubbly and depending on what type of honeycomb you’re looking for you can change your mold type. Deeper ramekins or cake tins for instance help create a thick honeycomb whereas spreading it out on a tray makes a thinner honeycomb. It’s easier for gas to escape from the thinner honeycomb so it might be a little less airy. Experiment with the best format for your purpose.

expanded sugar syrup

Which sugars should you use to make honeycomb?

For honeycomb to form that glass structure you need a good amount of sucrose to be present. Sucrose can form that glass and provide hardness. As such, most honeycomb recipes will contain a good amount of ‘regular’ sugar (e.g. granulated sugar) which is pure sucrose.

Can’t be just sucrose!

However, you can’t make honeycomb with just sucrose (as we tried below)! Sucrose is very prone to crystallization when you’ve concentrated it as much as you do for making honeycomb. As such, you need to add something to prevent the sugar from crystallizing. If you don’t, the sucrose will simply start to crystallize once you start stirring in the baking soda. It won’t be able to hold onto the air and become a crumbly white mess.

honeycomb made using different sugar syrups with composition
Notice the white flat sample on the bottom left? That’s been made with just sucrose. It started to crystallize as soon as we mixed in the baking soda, and barely held on to any air. It was the most flat of all honeycombs for sure.

To help prevent the sucrose from crystallizing, you can add a sugar syrup. That sugar syrup will contain other sugars aside from sucrose which help to prevent it from crystallizing. There are a lot of options here that can work, each will make a honeycomb with a slightly different flavor profile.

Glucose syrup / Corn syrup

Glucose syrup (called corn syrup in the US) is made from starches that have been broken down partially. As such, it contains small sugars like glucose and fructose, as well as longer chains of sugars. This mix of carbohydrates has a few advantages. The main one being that those long chains prevent the crystallization of sucrose.

Glucose syrup itself is bland in flavor and is slightly less sweet than sucrose, making for a moderate sweet honeycomb.

You can even make honeycomb with just corn syrup, not using any ‘regular’ sugar!

Specialty sugar syrups

In the Netherlands you can find a special sugar syrup called schenkstroop (which translates as pouring syrup). This syrup is dark in color and has quite a strong unique flavor but is very different from molasses. We tried making honeycomb with this syrup and that works very well. The flavor of the honeycomb is a lot stronger, even a little bitter, than the honeycomb made with corn syrup, but it works well.

Since this syrup works well we have no doubt specialty sugar syrups unique to other regions (e.g. kandijsiroop from Belgium) will work as well!

honeycomb made using different sugar syrups with composition
The Dutch syrup makes a dark, but very flavorful honeycomb. Corn syrup makes a lighter colored honeycomb with a great texture.

Honey

You can make honeycomb with honey! There are a lot of different kinds of honey out there, but they’re all made of a mix of smaller sugars and contain a good amount of fructose and glucose.

When you use honey to make honeycomb the flavor is noticeably different. Honey has a distinct flavor and this will transfer into the honeycomb as well.

Golden Syrup

Especially popular in the UK, golden syrup can also be used in honeycomb. Golden syrup is inverted sugar, that is, sucrose that has been broken down into equal quantities of glucose and fructose. As such, golden syrup only contains glucose and fructose and none of those longer molecules. This does make honeycomb made with golden syrup a bit more prone to stickiness. You might notice that recipes using golden syrup use a bit less liquid syrup compared to a recipe using glucose syrup.

How to store honeycomb

Honeycomb is crispy, and crunchy thanks to you boiling that sugar syrup to just the right temperature. This crunch is what makes a honeycomb fun and good to eat. Once it loses this crunch it becomes tough and rubbery and the ‘magic’ is gone, it might even start to lose some of those air bubbles.

Keeping honeycomb crunchy requires very much the same science as cooking the sugar syrup does: keep out the moisture. Additional moisture is detrimental. As such, you should always store honeycomb in an air tight container to protect it from humidity in the air.

Humid climates

Making honeycomb in a very humid climate is very tricky. All that moisture in the air would love to sit in and on the honeycomb you just created. Before that honeycomb has even had the time to cool down and harden it might have absorbed moisture. Your best bet: make it on not-so-humid days or in a climate-controlled space.

Why most honeycomb sold in supermarkets is coated in chocolate

Since honeycomb is so sensitive to moisture it’s hard to buy it ‘naked’ in most stores. Specialty candy stores might sell freshly made honeycomb since they will have sold it before it has time to get soggy. However, supermarkets and other larger outlets typically don’t sell it, it simply isn’t stable for long enough.

What you will find more commonly instead: honeycomb coated in chocolate. The chocolate takes over the role of moisture barrier. Moisture can’t travel well through chocolate and as such the chocolate coating protects the inner honeycomb from turning tough!

honeycomb made using different sugar syrups

Honeycomb

Yield: 8-10 portions
Prep Time: 5 minutes
Cook Time: 30 minutes
Total Time: 35 minutes

Making honeycomb isn't as complicated as you might think, but a fun chemical balancing act!

Ingredients

  • 100g sugar
  • 45g corn syrup (or any of the other syrups mentioned about)
  • 25g water (exact quantity not important, adding more will only increase the cooking time)
  • 1/2 tsp baking soda

Instructions

  1. Prepare a heat resistant tray/cake tin and cover with parchment paper.
  2. Mix the sugar and corn syrup in a pan and add the water.
  3. Bring the mixture to a boil and ensure that all the sugar crystals have dissolved. If they haven't, give the pan a very gentle swirl to help them along.
  4. Continue cooking the sugars until they are 150°C (300°F). The sugars will have started to brown but only slightly, this is ok, adding the baking soda will help it turn brown rather quickly.
  5. Take the mixture off the heat and mix in all the baking soda. Do this fast. Watch out, the sugar syrup is very hot and the baking soda will cause it to bubble up a lot!
  6. Immediately pour onto the heat-resistant surface and leave to cool.
  7. Once it's cooled down, break into shards. Either eat immediately or store in an air-tight container. The open sugary structure attracts moisture easily (it's very hygroscopic). Keeping it away from air will ensure you can keep it for a few weeks.

References

Andy Connelly, The science and magic of cinder toffee, The Guardian, 24-Sep, 2010, link

Nor Shuhada Binti Shoberi, The role of pH, temperature and catalyst type in caramel manufacturing process, 2010, link

Wikipedia, Honey, link, visited 12-May 2021

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