This could be opening up a whole can of worms - or rather a whole case of plonk - since I haven't checked the classification of other popular wine varieties. (Though I do know pinot is common, from the anagram set point, piton, pinto, pinot.)
However, the word riesling is used often enough to warrant common status, so the only issue is capitalisation. Almost all dictionaries agree with your spell checker, Jacki, and give a capital R, without the option. Why this should be is unclear, as it doesn't seem to derive from a place name. If the word was almost always written with a capital R, it might be justified to have it as a rare word, since many players might not realise it can be written without the capital letter. But it looks to me as if about 25% to 30% of the time it's written with a lower-case r, so I don't think many players would be surprised to see that it's allowed in Chi.
The word will be treated as common from now on. Cheers!
