There are different types of treacle, Black is only one, Golden Syrup is a lighter-coloured type of treacle and often substituted with corn syrup in recipes where black treacle is not available. In Britain, the main producer of black treacle (and Golden Syrup) is sugar refining company Tate and Lyle.
Roasted grapes are sophisticated. Toss grapes with olive oil, salt, and pepper, and roast them on a sheet pan for about 30 minutes at 425Â°F. The grapes will get blistered and caramelized on the outside, and extra juicy and practically jammy on the inside.
Yes, you can pick one grape, put it in your refractometer and take a sugar sample, but it won't be very representative of all your grapes. Instead, pick individual grapes from many clusters. Sample from both sides of the vine, high and low, in sunny areas and shaded areas, and pick from different parts of each cluster. An ideal sample might be 50 grapes. But if you only have a few vines, it'll be okay to take a smaller sample.