You don't have to modify recipes much when you make smoothies the day before, in most cases – just blend, store in an airtight container and enjoy within 24 hours. Some blended fruits and vegetables, though, are less conducive to overnight cold storage than others, so you might have to make a concession or two in the recipe to preserve quality. The flavor of some vegetables, such as kale, change overnight too, and not for the better, which also necessitates a little recipe modification.
Oxygen affects all foods, but some more readily than others. In the fruit group, peaches, bananas, pears and apples turn brown rather quickly, as do artichokes, cauliflower and potatoes from the veggie department.
Browning occurs when polyphenol oxidase, an enzyme in fruits and vegetables, comes into contact with the air upon slicing or peeling. Acids and sodium interrupt the enzyme action that causes browning, with citric acid fitting best in the flavor profile of most smoothies.
To prevent your smoothie from turning brown overnight, blend the juice of half a lemon (about 1 tablespoon) in with the ingredients.
The natural bitterness of brassicas, such as kale and cabbage, as well as cruciferous veggies (a type of brassica) such as broccoli and hardy greens, comes from glucosinolates they contain. When you slice vegetables containing glucosinolates, they release isothiocyanate, also known as mustard oil.
Depending on genetics, some folks detect isothiocyanate on the palate far more readily than others, making premade smoothies a bitter pill to swallow. And even if you handle the inherent bitterness of foods like kale with ease, you might not the next day; during blending, the mustard oils disseminate throughout the smoothie and intensify, similar to how the flavor of some dishes, such as braises, intensify when stored overnight.
You can stave off any potential bitterness in kale smoothies (or any brassica-containing smoothie) in two ways: Blend the kale into the smoothies just before you drink it, or add a touch of salt to ameliorate it. To prevent bitterness in veggie smoothies, mix a scant pinch of salt into the smoothie just before drinking it. Taste the smoothie and check if it's where you want it; if not, add another scant pinch of salt and check again.
How to Store
Store smoothies in food-grade airtight containers or glass jars in the refrigerator. Before serving, vigorously shake the smoothie in the container, or even reblend it in the blender for a few seconds, to recombine it.
- Add 1 tablespoon of lemon juice per 16-ounce smoothie to prevent browning.
- Add salt to brassica-containing smoothies before serving to minimize bitterness.
- Store smoothies up to 24 hours in the refrigerator in an airtight container.