" a tin of home grown stuff". Raises many questions. Our last years crop (picked mid year) roasted weirdly when we pulled it off the drying racks, but then started roasting it again 6 months later, and it roasted evenly and gave a delicious cuppa. SO.... like you, we hold our green' with parchment on, and then hull them just before roast, but not in a tin. Do you mean sealed .. with lid on? Ours breath in an open container.