I've read that any kind of mustard, and even some pretty mild greens like Brassica rapa Bok Choy or Chinese cabbage gives cow's milk an awful "mustard" flavor.
But 'Tyfon' (Holland Greens) was bred from a cross between stubble turnips
& Chinese cabbage to have NO "mustard oil" at all. It was first bred to be a forage crop / cover crop, but they are also OK as very bland, very very productive salad greens.
They're cut-and-come-again every 35 days, 60 DTM, or tender-when-young. They are very cold-hardy, allegedly down to 10F.
