Koulouri Thessalonikis (Κουλούρι Θεσσαλονίκης) is the sesame bread ring that anchors the whole koulouri family, and the version most worth describing in full because everything else is built on it. It is a circular loop of lean wheat dough, no fat to speak of, crusted heavily on every surface with sesame seeds. The name ties it to Thessaloniki, where it is the default morning food sold off carts and from bakery windows, but it travels: you find the same ring across Greek cities. Eaten plain it is breakfast in one hand; split open it becomes a vehicle for cheese, ham, or a sweet filling, and those filled forms each deserve their own article rather than being crowded in here.
The dough is the point. Flour, water, yeast, salt, and a little malt or sugar for color, kneaded firm and worked into a rope, then the rope joined into a ring. Before baking the ring is dipped: first into a thin syrup or grape-must wash, then pressed into a bed of sesame so the seeds bond to the wet surface and toast as the bread bakes. A good koulouri comes out with a crackling, deeply tanned crust, a chewy ring of crumb just inside it, and sesame that smells roasted rather than raw. The hole should be open and clean, the ring even in thickness all the way around. Sloppy work shows immediately: a pale crust because the wash was skipped or the oven was cool, bald patches where the sesame never stuck, a dense doughy center because the ring was too thick or underproofed, or a stale, leathery chew from a koulouri that sat past its few good hours. Freshness is not a bonus here, it is the whole proposition. A koulouri eaten warm in the first hours is bright and nutty; the same ring in the afternoon is a different, sadder object.
Within the plain form the variation is mostly regional and proportional. Some bakers run a thinner, crispier ring, almost a sesame breadstick bent into a circle; others go thicker and softer, closer to a bread roll with a hole. The sesame can be the pale tan seed or a darker, more aggressively toasted coat. Vendors sell them stacked on a pole or fanned in a paper sleeve, and the ring is sized to be torn and shared as easily as eaten whole. The filled and sweet versions, and the cart-sold street form, build directly on this same ring and are covered separately.