If you want to bake something with an orange flavour, recipes will more often than not, not use orange juice. Instead, you will use orange zest (or both). But why is that the case?
That orange zest is actually packed full of flavour and that flavour is actually different from that present in the orange juice! There’s a lot of fascinating chemistry involved and it has a lot to do with solubility of flavours in water vs. oil. We’ll dive into all the details.
The orange, its structure and the peel
Let’s start by dissecting an orange. If you look closely at an orange cut in half, you will see several quite distinct regions. The inside is the fleshy fruit itself, with its vesicles full of juice. This section consists for a large part of water of course as well as sugars and acids.
Around that juicy section there’s a whitish region and than a thin bright orange outer layer. Those two layers together make up the peel of the orange and it protects the fruit against heat, dehydration, insects and other pests.
Those two layers in the peel are very different though and not just in colour. The white region, also called rind or albedo, surrounding the fruit can be quite thick and bitter. You will notice it doesn’t really taste like orange. Instead, it’s quite bland and dry because of the higher amount of fiber. When you’re making an orange flavoured cake or pie, you would not use this white layer.
The orange outside layer (more on its colour here) is also called the flavedo. This layer smells a lot like an orange. If you rub an orange against your hand you will probably smell it already. Part of this flavour comes from the oil glands that reside in this layer. These are tiny pockets of oil inside the peel. The oils made in the glands serve as a defense system for the orange. However, it’s also these oils that have a strong flavour and aroma.
Apart from these oil glands the orange layer consists of a variety of other molecules such as waxes, various polymers and fatty acids.
How to make orange zest
Orange zest is what you get when removing just that outside flavourful orange layer from the orange. When making orange zest you want to be careful to just remove that outer layer, so you don’t want to handle the orange too roughly.
Good tools to use for making orange zest are a simple fine grater, a microplane is even finer, So, when you want to make orange zest, you only want to use the outside of the orange, the actual orange part. You do this by gently grating of the outside with either a fine grater (don’t use a rough one), a microplane or a zester (a small little tool that just pulls off small strands of the peel).
In some instances you use the zest to infuse something, for example cream of milk. You will remove the zest again later on in the process. In those cases you can also gently cut off a thin slice of the orange peel (again, don’t take off to much of the white) and use that.
Storing orange zest as an extract
If you can’t use all your orange zest in one go,there is a way to preserve it for longer, by making it into an extract. It’s very similar to what you would do when making a vanilla extract.
Since most of the flavours in zest are oil soluble they tend to dissolve in ethanol (= alcohol) quite well. Learn more about making such an extract in a separate post.
Using orange peel/zest instead of juice
When using orange peel we just use that section of the orange which has all these great flavours, the flavedo. The flavours in this section are quite concentrated. There is a lot of flavour in only very little peel. However, the contrary is the case for the juice. There is a lot of juice (water) with less concentrated flavour.
If you’re baking a cake you don’t want to add a lot of additional moisture, so you can’t use unlimited amounts of orange juice. The batter may become too liquid. It is a lot easier though to add a lot of concentrated flavour in the peel.
Fat vs water soluble flavours
And there’s another difference. The peel and juice actually taste and smell different. They contain slightly different flavour molecules. Part of this is due to an important concept in chemistsry: hydrophobicity & hydrophilicity. This concept refers to water molecules are water soluble (hydrophilic) or oil soluble (hydrophobic). Different flavours have different molecular structures. Because of these differences in structure, they can have a different preference of oil vs. water.
What you might have guessed by now is that the orange peel contains mostly oil soluble flavours, whereas the juice will contain more water soluble ones. Since these are actual different molecules, their flavours are also slightly different! The fruit has evolved in a way that the outside is suitable for getting rid of pests whereas the inside is an acceptable food for animals and a good protection for the seeds.
Flavour of factory juice
Have you ever noticed that store bought orange juice tastes different from freshly pressed one? This difference is very much country dependent, but one of the reasons actually is the presence (or absence) of flavours from the peel! Manufacturers of orange juice know that we expect our orange juice to taste a certain way and to strengthen that flavour they add some of the peel’s flavours into the juice. This changes the flavour profile!
Of course, addition of flavour isn’t the only add. Manufacturers also add back vitamin c, but that’s a wholly different topic.
Using orange zest
Orange zest is used in a lot of different recipes. You will find it in cakes, pies, ice creams and breads. In almost all cases you will use orange zest to add flavour. Orange zest won’t affect the texture of your product (which is often exactly why you use it). The most common way to use it is to just add some finely grated zest to a recipe and let it do its thing. That’s what we did when making waffles with orange zest or blueberry muffins.
As we mentioned earlier, in some cases you use the zest to infuse flavour at a step during the process, before removing it again. This is common to do for making ice cream, drinks or a pie filling for instance (and you can also do it for spices).
A study on the appearance of an orange
Tetrapak, Principles of processing orange juice (chapter 4), Orange book, link