bowl of caramel popcorn

The Science of Caramel Popcorn

Caramel popcorn is full of contrasts. Light, fluffy and airy inside with a dense outside, savory corn with a sweet, buttery caramel sauce. Vegetables + candy (yes, you’d almost forget corn is a vegetable).

The contrasts are what make caramel popcorn delicious, but they’re also what make it complicated. Balancing these contrasts, without them evening out over time is always tricky. It’s a challenge to balance the dry crunch with the soft outside.

Caramel popcorn is made up of two very different components: caramel + popcorn. By themselves, these components are pretty fascinating, combining them makes them even more interesting. Let’s have a quick look at the two individual components, before trying to put it all together.

The Popcorn

A good caramel popcorn starts with a well puffed popcorn kernel. We’ve written about popcorn quite extensively, e.g. on why it makes a popping sound, we’ve looked at the type of corn you need to make popcorn (not just any corn will do!) and we’ve shared several ways on how to make popcorn.

A long story short though, popcorn is made from popping corn. This corn is quite small and roundish. This corn is dried (while still on the stalk) to ensure you end up with a hard dry kernel that you can store for years until you decide to pop it. You pop the corn by heating it quite rapidly. The heat will cause all the moisture within the kernel to evaporate. However, it can’t leave the kernel due to the strong outside hull. This causes the pressure inside the kernel to go up a lot until it is too much for the hull to handle and it will pop! The pressure expands the starch within the corn, creating the white fluffy popcorn we’re used to.

corn kernel structure

Ideal shape for caramel popcorn – Mushroom vs Butterfly

If you want to coat something in a liquid (such as caramel or maybe a chocolate sauce) you’d ideally want it to be easy for that coating to spread over the center. While you’re mixing the corn with the liquid, you don’t want the popcorn to break into smaller pieces. Also, since the liquid is often more expensive than the corn itself, you don’t want it to seep into too many nooks and crevices, you’d need a lot more of it. It is why manufacturers of caramel popcorn prefer to use a popcorn type that is as round as possible. These round popcorn kernels are called mushroom popcorn.

If you’re making caramel popcorn at home though, it is more likely that you have a popcorn type called ‘butterfly’. This popcorn doesn’t pop in a ball. Instead, it’s quite irregular in shape, with various parts sticking out (‘wings’). This type of popcorn is generally considered to be the higher quality popcorn, however, does make it more complicated (but definitely not impossible!) to coat the popcorn.

Whether or not your popcorn is a mushroom or butterfly type isn’t influenced by how you pop it. Instead, most of it is genetically determined, though growing conditions can have some influence. Once that corn has been harvested, there’s no way to convert one into the other anymore.

The Caramel

Once you’ve got popcorn to be coated (see bottom of this post for a recipe) it’s time to start thinking about that caramel. There are a lot of different caramels out there. The simplest types consist of just sugar and water. More complicated varieties may contain ingredients such as milk, cream and butter.

Making caramel almost always starts by bringing the ingredients to the boil and cooking them until a pre-determined temperature. While you’re cooking the ingredients, you’re evaporating moisture, thickening the caramel. Also, the heat causes a variety of chemical reactions (mostly the Maillard reaction) to occur. These chemical reactions can change the color our your caramel (make it browner) and they’re very important for creating those characteristic caramel flavors!

Popcorn caramel criteria

When making a caramel for use on popcorn there are a few factors to keep in mind. First of all, you’d want the caramel to taste good with popcorn of course. Since popcorn itself is quite bland in flavor, most of the flavor will come from the popcorn. As such, add some salt for a punch of flavor, but at the same time, don’t make it too sweet or salty since there’s nothing to counter act it.

Second, the caramel should has the right consistency. A very runny caramel will just run off your popcorn into the bowl. Also, it will be impossible to eat, probably leaving you with sticky hands at the end. On the other extreme, it is impossible to coat popcorn evenly with a very thick caramel. The easiest way to control this consistency is through water. If your caramel is too runny, cook it for a little longer, to get rid of more moisture, that will thicken the caramel. If it’s too thick, add a little water.

stack of caramel popcorn

Bringing the Popcorn and Caramel together

Once you’ve landed on your popcorn and caramels, it’s time to bring them together. Whereas you can make the popcorn in advance, this isn’t the case for most caramels.

When you’re cooking your caramel, it will look liquid. However, most caramels harden when they cool down. Fats (e.g. butter) might turn solid, but also, at the lower temperature, the water in the caramel simply can’t move as freely anymore. This is a good thing to happen, it will help the caramel to set on your popcorn. However, it also means that your caramel should come straight from the heat (or shortly thereafter) when pouring it over the popcorn. Once you’ve mixed the too, the caramel will harden. However, you will probably want to harden it out just a little more!

Drying the caramel popcorn (in the oven)

A lot of caramel popcorn recipes will call for drying the popcorn in the oven, after you’ve mixed the caramel and the popcorn. When testing it out with the recipe below, we noticed that this step is not essential if you’re planning to eat all of your caramel popcorn within a few hours of making it. If you’re planning to hold onto it for a little longer, or want to make a bigger batch, it’s a step worthwhile doing!

Most recipes will tell to spread out the freshly coated popcorn on a baking tray and place it in the oven at a low/moderate temperature (145-150°C / 293-303°F) for quite a long time (up to an hour). So what happens during this time?

Not much, the popcorn shouldn’t change color or flavor. If it does, you still turn your oven lower. Really, the only thing that’s happening is the evaporation of more moisture from the caramel. This will dry out the popcorn just a little extra, helping it to stay crunchy over time and for explaining that, we should have a closer look at the concept of moisture migration.

Preventing moisture migration

Both caramel and popcorn contain only a small amount of water. However, they do both contain water and probably not equal quantities. If one contains more ‘available’ water (expressed in water activity) than the other, that water will want to move from one to the other. Generally, the caramel will have a higher ‘water activity’ than the popcorn. As a result, if you leave the popcorn for a while, moisture from the caramel will migrate into the corn. This causes the popcorn to lose its ‘crunch‘ and become soft and chewy.

It takes a while for this to happen, which is why the caramel popcorn won’t need further drying if you’re planning to eat it quickly. However, if you’re going to wait a while with eating it all, you want to get rid of some of that additional moisture!

Once you’re caramel popcorn has been dried enough, you want to make sure it stays crunchy for a while. It’s best to then store it in an air tight container or packaging material, that doesn’t let moisture through. Especially in humid climates your caramel popcorn will otherwise take up a lot of water, still making it soggy!

stack of caramel popcorn

Caramel Popcorn

Yield: 1 large bowl (>8 portions)
Prep Time: 5 minutes
Cook Time: 10 minutes
Additional Time: 1 hour
Total Time: 1 hour 15 minutes

This caramel popcorn is all about controlling and managing heat. Ensure your popcorn kernels pop but don't burn and that your caramel darkens, but won't turn black.

Don't skip the oven stage at the end, even though the caramel-coated popcorn at that time will taste great. The oven heat will make it even better and a lot less sticky!

We used a recipe from The Kitchn as our starting point.

Ingredients

For the popcorn

  • 115g unpopped popcorn kernels
  • 3 tbsp of oil (enough to lightly coat all kernels)

For the caramel

  • 170g of unsalted butter
  • 180g brown sugar
  • 30g corn syrup (optional, to help prevent crystallization)
  • 1/4 tsp salt (or add to taste, this quantity doesn't give a pronounced salt taste)
  • 1/4 tsp baking soda

Instructions

Popcorn

  1. Take a wok or sturdy thick-bottomed pot and add the oil.
  2. Place on a medium/large burner on a medium/high heat and add a few corn kernels in the pot.
  3. Cover with a lid and continue heating.
  4. Once you hear the kernels inside popping, it's time to add the rest. Add them, immediately close the lid and shake to cover all kernels with a little oil.
  5. Continue to heat on the stove. Make sure to shake the pot regularly, this ensures that the kernels at the bottom don't burn or get stuck. You'll hear more and more kernels popping.
  6. Once the amount of popping has died down, turn off the heat. Leave the lid on for a little longer, kernels might continue to pop (and fly out if there's no lid!).
  7. Pour the popcorn in a large heat-proof bowl where you can easily stir it around.

Caramel

  1. Add the butter, brown sugar, and corn syrup in a saucepan and heat on a medium heat.
  2. Stir to ensure the sugar is well mixed with the butter and has a chance to dissolve.
  3. Continue heating until the mixture is bubbling away vigorously and has reached a temperature of 145-150C (293-303F). (Unlike with other sugar candy, the exact temperature is not as important.)
  4. Stir in the salt and baking soda. Take care, the baking soda will cause it to bubble a lot!
  5. Use immediately (see text for what happens if you need to leave it on the side and how to fix possible issues that may arise from that!)

Caramel Popcorn

  1. Pour the, still hot, caramel over the popcorn.
  2. Stir the two together using a spatula or wooden spoon. Do so immediately, once the caramel starts cooling down it becomes harder to mix them.
  3. Spread out the popcorn on a baking sheet, breaking up larger lumps.
  4. You can now leave it to cool down. The caramel popcorn will taste good, but might be a little sticky and hard. If you want it lighter and crispy and not sticky, continue with the next step!
  5. Leave the spread out popcorn in a pre-heated oven at 120C (250F) for about 1 hour. Stir through every 15-20 minutes to prevent large clumps from forming.
  6. Take out of the oven, they're great ready out of the oven, but become even more crispy when cooled down completely.

Make sure to store these airtight! The caramel popcorn can attract a lot of moisture. As long as it's stored airtight it can be stored for at least a week at room temperature (shorter when it's warm due to oxidation of the butter!).

References

Betran, Javier., Betrán, Javier., Runge, Edward C. A.., Smith, C. Wayne. Corn: Origin, History, Technology, and Production. United Kingdom: Wiley, 2004. link, p. 913

Hallauer, Arnel R.. Specialty Corns. United Kingdom: CRC Press, 2000. link, p.214

Popcorn county, Sellers of both butterfly and mushroom popcorn (visited Jan-2021)

Water activity in foods, fundamentals & applications, IFT Press, 2007, link, p.419

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