Locust Grove Farm in Milton New York grows this apple and calls it Summer Pippin. I have my doubts about the name, but a box of these big green beauties at the Union Square farmers' market (New York) commands attention.
Granny Smith's unglazed hue. It's ribbed and lumpy, with a little russet radiating from the stem well and dotted with white lenticels. The firm fruit has a faint sweet smell.
The flesh is a dense white tinged with light green, a little yielding to the teeth. The taste is predominantly tart with some sweet, not as complex as a Granny Smith but reminiscent. There is some bracing acidity and a hint of unripe grapes.
Finally, there is a faint sweet citrusy aftertaste. Whatever you call it, this apple is both unusual and refreshing.
I shot the above in Central park. A more scenic image is here.
Update: Apparently the grower is now calling this variety "Greening Sour." That is helpful, since Summer Pippin is an old name for Champlain, a very different (and antique) variety.