
Baby spinach is the young, tender leaves of spinach, a leafy green vegetable.
Any mild leaf does the same job — chard, lettuce hearts, or a small handful of parsley if a green herbal note is welcome. Matcha colors more strongly and brings tannin and caffeine along.
Mature spinach
Bigger, tougher leaves with a stronger mineral bite and more oxalic chalk. Blended into a drink it colors the same and tastes noticeably louder: use about a third less, or the green takes over.
Kale
Also green and much more assertive, with a bitterness that comes through sugar. It is a flavor ingredient where baby spinach is mostly a color one, so the drink stops being merely green and starts tasting of the leaf.
A few days chilled in the bag it came in. Wilted leaves are past it: they blend to a duller green and taste of the fridge.