A lot of candy bars and other confectionery products are coated with chocolate. The problem with chocolate is that you cannot simply melt it in a pot and then dip your candy in it. We need to temper a chocolate mass every time we melt it to obtain the right crystal structure.
Firm chocolate consists of about 80 percent crystalline fat and 20 percent liquid fat. You can produce softer chocolate by increasing the liquid fat content for example by the addition of milk fat or vegetable oils. The reason why dark chocolate is much firmer than milk chocolate is the higher solid fat content.
When we heat the chocolate to liquify it, we melt the crystalline fat so that it turns into liquid fat. As soon as we then cool down the chocolate, the recrystallization of the cocoa fat begins. Cocoa fat can form six different types of crystals. We call this phenomenon polymorphism.
These six crystal forms have different melting points. Take a look at the table below:
| Crystal form | Melting point |
|---|---|
| I | 17.3 °C |
| II | 23.3 °C |
| III | 25.5 °C |
| IV | 27.3 °C |
| V | 33.8 °C |
| VI | 36.3 °C |
As you can see, the crystal forms I and II are prone to melt at room temperature. Form III and IV allow us to produce firm chocolate but it isn’t firm enough to give us a good snap.
Form V is the preferred crystal type for chocolate. Why not form VI? Because we want the chocolate to melt in our mouth. Our body temperature is 37 °C. If we put chocolate that melts at 36.3 °C in our mouth, the temperature difference between our mouth and the melting point of the chocolate is not high enough to give us a good melting behavior. Crystal form V melts at 33.8 °C which is 3.2 degrees colder than the temperature in our mouth. The chocolate will have a great snap and it will melt on our tongue.
How do we achieve that our chocolate consists primarily of crystal form V? We temper it. That is we undergo a strict heating and cooling regime that favors the growth of crystal form V.
How to temper chocolate
You correctly temper chocolate the following way:
- When working with chocolate, always work with a metal bowl that is set over a saucepan of simmering water. You don’t even want the bowl to touch the simmering water. The steam coming from the simmering water is enough to heat the bowl for chocolate tempering. If you would heat the chocolate directly in the pot, it is very easy to overheat it.
- Take about two-thirds of your chocolate mass and gently heat the chocolate to 48 °C (120 °F) for dark chocolate and 40 °C (105 °C) for milk chocolate. At this point, all the fat in the chocolate is completely melted.
- Now you can take the chocolate off the heat and start to slowly stir in the remaining third of chocolate (this remaining third of the chocolate introduces the form V seed crystals into the system). After that, you need to wait until the chocolate reaches 28 °C (82 °F) for dark chocolate and 26 °C (79 °F) for milk chocolate.
- Reheat the chocolate gently to 31 °C (88 °F) for dark chocolate or 29 °C (84 °F) for milk chocolate. Now you can use your chocolate for coating candy. It is properly tempered. If you let your chocolate cool down and resolidify after tempering, then you need to temper it again before using it.
Why do we reheat the chocolate to 31 °C (88 °F) after it has cooled down to 28 °C (82 °F)? Remember the table with the melting points of the cocoa butter crystals that I have shown you. All the crystal forms expect form V and VI melt below 31 °C (88 °F). At 28 °C (82 °F), we induce the crystallization of the cocoa fat because we are far below the melting point of form V and VI crystals. Then we raise the temperature again so that we are a few degrees above the melting point of form IV crystals and so that the chocolate is liquid enough to be used for glazing.
What we are doing when tempering chocolate is to only allow crystals of form V to exist in chocolate. By stirring the chocolate, we redistributed the form V seed crystals all around the chocolate mass. Then when the chocolate has set after it has cooled down, it will be full of form V crystals because form V seed crystals act as a template for the final crystal structure.
Form VI can’t exist in tempered chocolate because it can’t be directly formed from melted cocoa butter. Form VI is always formed by a solid-to-solid transformation from form V to form VI crystals during the storage of chocolate. If form VI crystals could be formed directly from liquid cocoa butter, tempering chocolate the way we do it at home wouldn’t work. The tempered chocolate wouldn’t melt in our mouth as it would be full of form VI crystals.
What happens during the storage of chocolate?
Form V crystals are stable for several months up to a few years but they will over time be transformed into the most stable form: form VI crystals. This is the reason why old chocolate doesn’t melt in your mouth. If the fat hasn’t gone rancid during storage, you could still save an old chocolate bar by retempering it. It will have the same structure and melting properties as when it was newly purchased.
Another phenomenon that is happening during chocolate storage is called Ostwald ripening. During Ostwald ripening, many smaller crystals grow together into fewer larger crystals. These large crystals make the chocolate appear gritty and large crystals melt much more slowly than small crystals. But this can also be reversed by melting the chocolate and tempering it.
What cannot be reversed is, of course, lipid oxidation and the resulting rancidity of old cocoa butter. Another process occurring during the storage of chocolate-coated confectionary products is diffusion. Low-melting liquid fats from the filling will diffuse into the chocolate coating and thus soften the chocolate over time. But not just that, the filling will also get firmer because of parts of the cocoa butter from the chocolate counter-diffusing into the filling.
Chocolate and chocolate-coated confectionery products taste the best when they are fresh. So always consume them within a few weeks for the most indulgence. Chocolate is not made to be stored for a long time.
That’s all the background knowledge about chocolate that you need to know for candy-making. In the next part of my candy-making series, I will introduce you to recipes containing chocolate.
