I agree with Eric, the esters are fleeting because of age. Weissbier is best drunk fresh, 5 days of primary fermentation and a couple of days after force carbing the beer is ready to drink. After a month, the esters really start to fade. Which is one of the reasons I haven't brewed a weissbier in a decade, as much as I like them, as I'm not one to kill keg in a month anymore. A local craft brewery has a great weissbier on tap in the summer, getting a growler or two in the hot summer months is good enough to quench my thirst for them.