I checked with my fave meat supplier Sheepdrove Farm (100% grass fed beef and lamb, 10% off if you say you found them through me :)) and they said:
After talking to a few people we have concluded that the butcher’s string is coated/polished in a potato starch called Farina. Apparently this is done to stop the string unraveling and it makes it easier to tie the butcher’s knots.
In this case, I think farina means potato starch. Potato of course we know is a cross-reactive gluten food, so the body could well react to it the same as it would to gluten.
But ‘farina’ is a general term meaning flour in a lot of places so, in reality, it could be any cereal too.
Moral of the story: ask your butcher not to use string and if you do have some meat tied up, remove the string and wash the roast thoroughly.
There you go. Never say I don’t follow up your queries, even though it might take me a while…!