The hover event in jQuery takes 2 callback functions. The first one is triggered when user hover the item and the second for when it leaves
Try
$(".zentriert").hover(
function() {
if(!$(this).is(".open")) {
$(this).animate({opacity: 1}, 150);
$(this).find('img').css({'position': 'relative'}).animate({top: -10}, 150);
$(this).find('.beschreibung').css({'display': 'block'}).animate({opacity: 1, top: -10}, 150);
$(this).addClass('open')
}
},
function() {
if($(this).is(".open")) {
$(this).animate({opacity: 0.17}, 150);
$(this).find('img').animate({top: 10}, 150);
$(this).find('.beschreibung').animate({opacity: 0, top: 10}, 150).css({'display': 'none'});
$(this).removeClass('open')
}
}
);