Another easy one is asking about their favorite wine/beer, seeing if they seem interested in it's similarities and differences to other styles, and can reasonably defend why this is their choice. I usually feel like people who can talk about these things 1. In relation to food/flavor and 2. In relation to setting/mood have at least a reasonable amount of interest.
How carefully do they cook their pasta? what is their favorite family of cheeses? brand of tahini? etc.
In my experience, when one obsesses about food, one sweats the small things that make a difference, and delights in them. Terroir, in other words.