have now managed to get a packet and can't believe the difference in taste from normal cumin (which i'm not particularly keen on).
the black cumin i can eat out of the bag.
i've used them so far in making the ashoka rogan josh sauce and felt they gave a much better result.
they seem to be only available in small bags (100g c/w 300g for the std stuff) and cost approximately x2.
i'm nervous as to how much they are used by BIR's given the price. i can see them being used in marinades for sure (when the amount used is small but the flavour improvement is large). i'm not sure on use in spice mix but certainly going to try it out when making next batch.
overall this bag is going into my store cupboard as a standard item.
