Rancidity occurs when it goes off Willow my love. So just be careful that you either use it up in about 7 days OR just put out 75g at a time... As you know I live in Qld (though in a cool clime) and my butter is out on the bench in a butter dish all year around. There has admittedly been a couple of times that it has melted a bit - but not gone rancid...