Why does banana smoothie turn brown?

You hop onto a blender with three frozen bananas, half an orange and a little quantity of plain old yoghurt to perhaps turn up the mix, then you begin pulsing intermittently, to your heart desire, a very creamy milkshake guaranteed to make even Gordon Ramsey forget his very special name.

But then there’s one problem, every time you try to store the smoothie for just a little while, you end with a version the exact shadow of the one you left in the cup.

A brown, disgusting, piece of slurry. But why does this always happen? Why does banana smoothie or some smoothies in general quickly trade off their lustrous vibrancy for a brownish coloration?

The answer is very simple.

Banana smoothies turn brown because the elements of banana fruit in them readily oxidize to create a compound called melanin which is responsible for turning the smoothie brown or grey.

So the entire change you see when your banana smoothie turns from lustrous yellow to brown is nothing but a chemical change. And opposite to what you’re thinking, it’s a completely safe phenomenon to deal with.

Banana purees that have their colors changed are entirely safe to consume the way they are, except when they reek of rot, in which case, they should be promptly discarded.

What really happens when banana smoothies turn brown, and how exactly does it happen?

All bananas have an enzyme called polyphenol oxidase or (PPO) which is responsible for the famous process called enzymatic browning, otherwise comprehended by the regular Joe as the normal browning of banana peels and also that of the fruit’s flesh when cut and left to sit on the counter or in the refrigerator.

Fresh banana fruits in their entire wholeness and when they are free from squeezing, injuries and squashing do not undergo enzymatic browning because their cells are perfectly in place and intact, which further dictates that all the chemical compounds necessary for the browning process to occur are fully separated from one another.

But the very moment you decide to pop a fresh banana fruit into the blender for a special treat, you destroy the cells of the banana and therefore release and bring together the three main compounds necessary for the browning process to occur. They are, PPO, phenolic compounds and oxygen.

These three react to form quinones which then react with other released compounds in the banana cells to form something called melanin. Aha, now something very familiar has popped up! Melanin!

That’s the same melanin (the dark brown pigment in dark skinned people) that is responsible for their skin pigment, hair color, and eye color to mention but a few.

It is this melanin that turns the grinded or blended banana brown or grey, and this can happen in as little as a half an hour.

How to prevent banana smoothie from turning brown

In a true sense, you can never really stop a banana smoothie from turning brown, but you can at least slow down the browning process by the addition of acidic substances like lemon juice, vinegar and lime juice when you taste buds doesn’t mind the tanginess and extra note additions.

These somehow find a way to inhibit the activity of PPO in banana cells which reduces quick browning.

Don’t be fooled by thinking that the refrigerator will work in your favor to prevent smoothies from browning. It won’t.

It will only slow down the darkening process just like lemon and lime juice would, but the smoothie will eventually give in to both browning and texture degradation, no matter how tight the container sealing is or cold the refrigerator compartment is. That’s two zero!

Alternatively, you can make the smoothies exactly when you need them, since they are very easy to make. Aren’t they?


Are you that lazy?

What to do with banana smoothie that has turned brown

Eat it. Banana smoothie that has just turned brown has only lowered half of it’s its aesthetic value (in my own humble opinion), but never any figure in it’s nutritional quality.

Brown banana smoothie is perfectly safe to eat so long it hasn’t been preserved for more than a day in the refrigerator (don’t store banana smoothie on the counter). Feel free to enjoy it as you would the lustrous version.

Final verdict

As mentioned above, banana smoothies turn brown because of a process known as enzymatic browning which occurs when the banana cells are shattered to release and mix compounds that react to produce a dark brown pigment known as melanin. It is this melanin compound that gives the banana smoothie a room temperature tan.

Despite the unattractive look of a browned banana smoothie, it is perfectly safe to consume without any health implications.

When next you have a cup full of toilet type material, feel free to spark life with a quick spoon mix and gulp every little sip like you paid a lifetime savings for it.