Vendors judge freshness by that day's batch only — a stack of pre-fried skewers gone cold is treated as a giveaway of a bad stand among locals.
Mussels are threaded onto skewers, dipped in a light batter, and deep-fried until golden, then served with a garlicky walnut-tarator sauce for dipping. Istanbul's meyhane (tavern) streets, especially around Beyoğlu, sell them by the skewer as a beer-drinking snack.
Why it's made this way: The Bosphorus and Marmara Sea's rich mussel beds made shellfish a cheap, abundant street snack in Istanbul, and midye tava grew up alongside the city's raki-and-meyhane drinking culture as the fried counterpart to raw stuffed midye dolma.