No you don‘t.

Hola Antonio. Se puede hacer la "cata" de vinos sin reservar. En realidad es pedir unos vinos y tomártelos. Tienes un papel informativo de cada vino pero no hacen cata no te explican nada. Yo pediría un número pequeño de vinos ya que para mi gusto no son demasiado buenos. El precio sobre unos 16€. Merece la pena ir al atardecer.

Hi cc 1689, when you arrive at the port in Santorini, just ask for the taxi rank near the main square, the taxi will take less than 10 minutes to Santo winery. Make sure you book a table in advance as it does get busy for lunch or dinner. Obviously dinner is the best time to see the beautiful sunset, if you’re having lunch, it’s still a magnificent view of the Caldera from your table. Ask for a table at the front, beside the glass barriers at the edge of the cliff top. Cheers Peter C (Melbourne Australia)

I would keep chasing them I can’t recall cancellation t&c

I saw only wine varieties in their boutique outlet onsite.

We were at the restaurant, so I don't know the link. Since there was no one there but us, we couldn't get over the fact that they wanted 50 Euro per person to sit in front.