In mid to late August cobnuts are picked in their green state. (At this stage they have a flavour more like a pea than a nut.) Once picked they are best treated as fresh produce and kept in a fridge using a well ventilated container. Alternatively they can be stored in cool dry place in a perforated container or basket. They should be turned or shaken each day to prevent them from sweating and becoming mouldy.
Over about the next month the husks of the nuts on the trees will gradually change colour from green to brown. By this time the nut will be developing a real nutty flavour that will intensify as the nut dries and becomes mature. At this stage the husk can easily be removed from the shell and the nuts stored in a cool, dry, place with good ventilation. Turn or shake them every couple of weeks.
Cobnuts have a long shelf life and if stored carefully will easily last until you are ready to pick the next year's crop.