While drinking a glass of freshly made orange juice a little while ago I noticed orange juice is a great vehicle for explaining all sorts of science related phenomenon. In the first post I introduced the orange, in this post, we’ll be focussing on making the orange juice itself.

We’ll start by discussing the two ways in which you can make orange juice: juicing vs. blending. Is one better than the other?

Two ways to make orange juice

There are of course a lot of ways to make orange juice, however, when simplifying them, we end up with two basic methods.

Method number 1 involves peeling an orange and using the rest of the peeled fruit, so the complete parts to make orange juice. I would generally do this by using a blender of some sort. I call this the blender method.

Method number 2 is to use only the juice of the fruit, so not the fibers and structures making up the different orange parts. You could cut an orange in two parts and push out the juice or use a machine to do this, or a juicer. I call this method the juicing method since it pushes out only juice. In some cases recipes call for filtering this freshly made juice, getting rid of any fibers that may have come with it.

Splitting of orange juice

A freshly made orange juice which has been made using a blender or any other method in which a lot of the skins of the orange parts gets into the juice, has the tendency to split. This phenomenon is very similar to what we discussed with chocolate milk.

However, in this case, instead of particles floating down (as was the case for the chocolate milk), particles float up!

Why does orange juice split?

Let’s start at the actual reason orange juice even separates. Freshly squeezed orange juice consists of roughly two components: water (with a lot of dissolved molecules, such as sugars, vitamins, minerals) & pulp. The pulp consists of the juice vesicles of the orange. These vesicles hold on to the water/juice when the orange is still whole. However, when making juice these are broken and most of the water flows out.

When not filtering the orange juice and blending your whole orange, these vesicles will still be present in the juice. The same goes up for the ‘walls’ of the orange segments. Both contain quite a bit of polysaccharides and have a light and airy structure.

Stokes’ law and orange juice

The reason that the orange juice separates is due to sedimentation of these fibers/polysaccharides.

Sedimentation is described by Stokes’ law. I won’t go into the physical details here. But the law results into an equation that states that the density difference between the fluid and the particles determines whether they will split, how fast that split proceeds and which of the two goes up and which goes down.

The component with the highest density will be pulled down whereas the particle with the lowest density will float to the top.

In the case of orange juice the pulp, all the loose fibers, have a very low density. They are wide open structures, thus they tend to float to the top. There’s nothing wrong with the juice splitting, just give it a little mix and it’s a normal juice again.

Manufacturers of orange juice don’t like orange juice to split like that though. Therefore they will homogenize the juice, making the pulp spread throughout the juice better since it’ll be of a smaller size.

Nutritional difference

There are quite some debates going on as to whether fruit juice is healthier or not than a regular soda. Even though I don’t like involving myself in nutritional discussions (it’s often presented as being black and white, whereas nutrition is often grey), I’d like to discuss this as objectively as I can :-).

First of all, why would orange juice be just as unhealthy for you as a glass of soda? Main reasons mentioned is the high sugar content and very low fiber content. Orange juices you find in the supermarket are often filtered and don’t have any pulp in them (thus no fibers which are good for you). Another thing is that eating an orange takes time, to peel, eat and chew. There aren’t a lot of people who would eat three oranges in a row. However, you easily drink an orange juice made from three oranges. All in all, you’re consuming a lot more calories a lot easier, without getting the positive benefits of eating fibers.

When blending orange parts into an orange juice you drink a whole orange. You would drink the exact same as when eating it. Only difference, you might consume a lot more oranges.

However, when juicing an orange you take out the fibers. These have a high nutritional value. You’ll be left with a sugar rich drink with some vitamins and minerals. Not as good as when blended.

I do want to note though, that everything should be enjoyed in reasonable quantities. So saying ‘orange juice is unhealthy’ doesn’t really cover it. It’s better to say, lots of orange juice is unhealthy, but that goes up for just about any food…

Sources

There’s a lot out there on orange juice, one I used is this book on citrus fruits.