I want to buy a large pack (25kg) but i will only use 10kg to start. How long can I store the rest? How long can they be stored if crushed?
It depends on what type of malt but assuming you are looking at base malts this should be accurate, It's directly from Briess's website referring to 2 row pale malt. Darker roasted malts will differ somewhat.
STORAGE AND SHELF LIFE Store in a temperate, low humidity, pest free environment at temperatures of <90 ºF. Improperly stored malts are prone to loss of freshness and flavor. Whole kernel diastatic and preground malts are best when used within 6 months from date of manufacture. Whole kernel roasted malts may begin experiencing a slight flavor loss after 18 months.