It’s common for the flesh of many fruits such as bananas to turn brown when exposed to air. This process is commonly known as oxidation. Apples and avocados are examples of other fruits that will brown over time once they’re cut open. While freezing pre-sliced bananas slows down this oxidation process dramatically, it does still occur.
It’s important to note that while your frozen banana slices will start to turn an unappealing brown color over time, that’s fine! The oxidation process is harmless and does not impact the nutrient quality of your produce. No matter how brown it gets, your frozen goodies are perfectly safe to eat when you’re ready for them.
If you’re someone that eats with your eyes before your mouth, there is one handy trick you can consider to stop your bananas from browning. Before freezing your slices, squeeze a little lemon juice over them. The acid from the citrus fruit will inactivate the enzymes that cause browning to occur. I like to use this method for the bananas that end up in my smoothie shakes. The extra flavour from the lemon juice adds a nice bit of zing.
Why Do Bananas Turn Black When Frozen?
When it comes to whole bananas, if you freeze them you’ll find that the skin rapidly changes color, turning brown then black. This process also occurs when you refrigerate them, but is accelerated when you throw them in the freezer. Why is that?
Bananas turn black when they’re frozen because the water content that is present in the fruit transforms into ice crystals. These ice crystals expand and cause cells in the banana skin to rupture. The rupturing of those cells releases polyphenols, which speed up the blackening process.
As with the pre-sliced banana slices, a change in color is nothing to be concerned about, and your whole banana remains perfectly safe to eat.
When it comes to freezing whole bananas versus pre-sliced, one noticeable difference is their post-thaw state. Compared to pre-sliced pieces, you’ll find that whole thawed bananas are mushy. The thawed banana is mushy because when it was stored in the freezer, ice crystals formed and expanded, breaking cell walls within the banana. As it defrosts, the ice crystals turn back to water, and those broken cell walls collapse, leaving you with a liquidy, mushy end product.
That mushy goodness is perfect for baking. When you cut open your defrosted banana, make sure you’re also including the accompanying liquid in your recipe! That sweet, liquid goodness is a big part of the flavour that goes into your banana bread or muffins.