In my post about the history and production of sugar, I have already hinted that I will one day write about candy production because it is another one of these fascinating topics. The basis of all sugar confectionary is a mixture of sugar and water. And just like bread, which is basically just flour and water, countless different candies exist with a great variety of flavors and textures.

It might seem that all these candies follow a very different and complicated production process. But if you take a closer look you will quickly find out that just like with bread, candy production follows a few very simple principles. Many people think that it is hard or impossible to make cough drops, gummi bears, or marshmallows at home.

It’s because we only know these products from the food industry. Candy is cheap. There is no point in making it at home because it takes effort and time to produce it. However, most candies are easier to produce than, for example, a homemade pizza.

The most important thing is to understand the basic principles behind candy production. If you know these principles by heart, there’s no need to rely on recipes. In the end, the production process is almost always more or less the same.

A short physics lesson

To understand the production of candy, it takes a little physical knowledge. The basis of all confectionary products is a syrup consisting of water and sugar. You might remember from physics or chemistry class that substances like water or sugar have a defined melting and boiling point.

Ice melts under atmospheric pressure at 0 °C and turns from a solid into water. The melting point of sugar under atmospheric pressure is at 186 °C which means that it is a solid at room temperature. If you heat sugar in a pan above 186 °C it will melt, break down, and caramelize.

If we make candy, we work with a syrup. The syrup is a two-phase system. We call this a binary water-sucrose system. Typically sugar syrup gets heated up in candy production to evaporate excess water.

Our binary system, the syrup, is neither fully water nor fully sucrose. It is a combination of both and thus it has, depending on its composition, a melting and evaporation temperature that is neither that of sucrose nor water.

The higher the sucrose concentration in the system, the closer the boiling and melting point of the system will get to the boiling and melting point of sugar. You can observe that by boiling sugar syrup. The more water gets evaporated, the hotter the syrup gets. Sugar doesn’t evaporate at 100 °C and can be heated much higher than that. The melting point of sugar is at 186 °C.

The phase diagram of a sucrose-water mixture

Take a look at the boiling line in the chart below. The higher the sucrose concentration, the higher the boiling point of the system. Thus we can exactly control the water content of our candy by cooking the syrup to a specific temperature.

The texture you have in your candy is dependent on the water content. Hard-boiled candy has a water content of only 1 % whereas chewy candy and gummy bears have a water content of about 6 %. Soft candies like caramel fudge or marshmallows have the highest water content, about 10-25 %.

Sugar syrup does not take on any color while it boils away. It doesn’t caramelize. Even hard-boiled candy syrup with only 1 % of water is transparent. Caramelization only starts once all the water has been evaporated off.

So how can it be that fudge is soft and caramelized? To produce fudge, you use milk to initiate the caramelization. Milk contains proteins that can react with the sugar to form dark flavor components. This reaction is called the Maillard reaction and happens much earlier than a pure sugar caramelization.

What phase diagrams are useful for

The greatest thing about the phase diagram of sucrose and water is that we can use it to draw the production process of different candies in it. It can work as a recipe without words. We are also able to see what kind of consistency and texture our candy will have after the syrup has cooled down to room temperature.

Take a look at the production process in the graph below. This one is for the production of hard-boiled candy with water content below 1 %. You start by preparing a 60 % sugar syrup at room temperature. You bring that syrup to a boil. Then you travel along the boiling line as the water evaporates and the syrup gets more and more concentrated. Just before all the water is evaporated off, you remove the syrup from the heat and let it cool down to room temperature.

Point 4 in the phase diagram above shows us that our hard-boiled candy is a glass. It is hard and brittle and you can’t chew it. Instead, the candy will slowly dissolve in your mouth when you lick it. It’s a cough drop or a lollipop.

Let’s compare the production of hard-boiled candies to that of marshmallows which have a higher water content of about 30 %. Take a look at the phase diagram below and see where we end up.

The syrup for marshmallows gets cooked to a lower temperature because the final product needs to have more water in it to be soft. As you can see, this time we don’t end up with glass but something in between a glass and a solution: a soft rubber (crystal + solution field in the phase diagram shown above).

Rubbers are chewy. The chewiness depends on the water content. The lower it is, the chewier and firmer the candy. Whipped products like marshmallows are only a little chewy because they contain a lot of water and have air whipped into them. A marshmallow is a foam and thus soft. If you would reduce the water content in your marshmallows to only 10 percent you would end up with a less airy and much chewier product.

But never go below the glass transition line. If you do that as you would for hard-boiled candies, your rubber will turn into a hard and brittle glass. You also can’t produce a rubbery candy without additional thickeners if your sugar content is below 65 %. If you are below that threshold your candy will be liquid at room temperature. You are in the solution field. You will end up with a thick syrup.

The difference between amorphous and crystalline solids

Now you might ask yourself: What even is a glass or rubber? Granulated Sugar as we buy it in the store consists of many small crystals. It is neither glass nor rubber. It’s a crystalline solid. That is because the granulated sugar has been crystallized in the sugar factory.

The crystal structure is a highly ordered structure and the only stable condition for a solid like sugar to be in. A glass or rubber is an unstable structure characterized by a low order of molecules. We call that an amorphous material. Glass is basically a liquid in solid form. Over a long enough time frame, rubber or glass will crystallize naturally. However, that time frame can be hundreds of years.

The reason why the sugar in candies doesn’t fully recrystallize immediately is that it takes energy and time to form crystals. If you cool down the candy to room temperature within less than an hour, the crystallization process gets slowed down to a minimum. The lower the temperature, the slower the crystallization rate. Also, as you cool down the sugar the viscosity of the product increases. A hard-boiled candy is tough and brittle. The molecules can’t move around freely. This inhibits the molecules from forming crystals by bumping into each other.

Nevertheless, if you only use table sugar in candies some part of the sugar will always crystallize. The way to prevent that is by adding glucose or inverted sugar to the syrup which inhibits crystallization.

In the phase diagram below, you can once again observe the three states of candy: syrup, rubber, and glass. Rubber is a super-saturated syrup that will crystalize over the long term and separate into sugar crystals and a saturated syrup. The same is true for a glass which is a liquid in solid form. Over a long enough timeframe (that is of no practical relevance) it will also turn into a crystal. You can observe this by trying to dissolve 90 g of sugar in 10 g of water. What you will get are tons of sugar crystals that won’t be dissolved in water. There’s too little water to dissolve all the sugar. This is also what your candy will look like if you leave it on the counter for possibly hundreds of years. Expect that it won’t consist of many small crystals. The sugar will most likely grow into one large rock sugar crystal.

By heating the syrup for candy production, you are using the laziness of nature to your advantage. You supply energy to solubilize the sugar in water but then the excess sugar in the syrup doesn’t recrystallize once the syrup becomes oversaturated because it takes energy to do so. The syrup just says screw it and turns into a rubber or glass.

It’s as if someone is using his energy to mess up your room. You might see that and then say to yourself: “Who cares, I just leave the room messy like it is. I have no energy to clean now.” But over a long enough time frame, by cleaning the room not at once but a little every day, your room might look clean and ordered again sometime far away in the future. The sugar is doing the same thing. It will continue to crystallize very slowly over a long time frame until completely crystalline. But it is a slow and energy-consuming process which is why candy has a long shelf-life of several months up to years.

The candy temperature chart

By now it is hopefully clear that the key ingredient in candy is water. The water content of the candy will determine its texture. If we don’t add any liquid to our sugar we can only produce a glassy caramel but no chewy or soft candy that is in a rubbery state.

We control the water content of our candy by cooking syrup to a specific temperature that corresponds to the desired water content. There are 8 basic temperature ranges that will yield candy with a different texture and flavor. These are shown in the table below.

The values given above are valid if you live at sea level. For every 300 meters above sea level, you should subtract 1 degree Celsius or 2 degrees Fahrenheit from these values because water boils faster at higher altitudes. I live about 250 meters above sea level so that the temperatures given in the chart above are accurate for me. However, if you live at a high altitude, you need to adjust the table above.

It’s best to use a thermometer when making candy. However, people have been making candy long before they had candy thermometers. You can also judge the syrup consistency by dropping a small sample of the syrup in ice-cold water. It will solidify immediately and you will be able to experience the final texture. However, for this approach, you should be familiar with what the final texture is supposed to be like in your recipe.

There’s a risk to misjudge the syrup consistency. But if that ever happens to you you can always reheat the syrup. Or, in case you overheated the syrup, you can always add water and boil it off again until you reach the desired consistency.

What happens after the syrup production?

The other ingredients for candy besides the sugar syrup are usually mixed with the syrup after it has been heated and taken off the stove. If you add vanilla to your candy, you don’t want to boil off all the volatile aroma compounds while preparing the syrup.

Hard-boiled candy usually has aromas and coloring agents added to it. A syrup for soft-boiled candy might be mixed with butter or cream whereas marshmallows are gelatin that is whipped with the syrup until light and fluffy. For a nougat, you whisk the sugar syrup into beaten egg whites. For a nut brittle, the syrup is mixed with nuts. There are countless possibilities.

Over the next few posts in this series, I will cover the production of special candy products in detail. There are so many of them that one single master post would be exhaustive. Today’s post was just there to introduce you to the basic background knowledge required to understand the candy-making process.

Now you know why the weather and humidity play such an important role when producing candy. There’s a good reason that some people say to never make candy on a hot and rainy day. Also, it should be very obvious by now why candy has to be wrapped individually in foil to prevent it from taking up water or drying out. The water content determines the quality of candy and even a slight deviation might result in a drastically different texture.