It really depends where you fly from. If the departure point does not have a kosher kitchen (eg PRG, MUC, WAW etc etc), and economy kosher meals are long-life (Stogel etc), chances are that business class will be also - Stogel businesss class meals are just as bad as the economy ones. If there is a kosher kitchen (eg LHR, CDG, JFK) the kosher business class meals should be as good as the regular ones (sometimes better!).

Sometimes you just get the economy class kosher meals on plastics, if demand is low at the departure point - I have had this in business (and first!) class from YVR, SYD, BKK etc)