How do you know when Tomatillo is ripe?

Hello,
Have grown a couple of Tomatillo plants on allotment. Have found that leaving the fruit inside the case until the case has dried up results in mushyish tomatillos. However the ones I've picked that aren't mushy seem a little under ripe. Does anyone have any ideas?

Thanks, have not tried them yet. I was planning to use them in a salsa of some sort as well