As germanbrewer said, I too worry it is simply freshness of ingredients. Is "it" a volatile compound in the malt that dissipates after a month or two of storage? I don't know.
That's my thought. The "good" German beers I've had have all reminded me of the way one of the local wheat fields smell around when the grain is close to being dried and ready for harvest, but isn't dusty yet. Especially if you drive past a field at night with the windows down.
But what do I know? I haven't even tried to brew a lager.
I do think the German beer home-brew community needs to try and better describe the flavors they're striving for, things like "IT" just confound and frustrate people looking for quantifiable answers.
You got it, that's a good description of it...smell of a field of fresh grain.
I've been working on it as the descriptors go. I've been researching this for several years, and found some buds on the same quest. Then the German beer market is really odd, with its history and Reinheitsgrebot and Biersteuergesetz, former kingdoms with their own styles (e.g. Franconia and Bavaria), and pretty traditional customer base. It's not like the US craft beer market. But that's changing there, too. Anyhow, it seems to be a fairly insular group (in Germany - maybe largely due to language and culture, the average dude like any of us is not chasing down breweries there to learn how to brew) and not a lot of information is as easily accessible. Kai Troester and a few others have done incredible work to translate Ludwig Narziss's works into English so we have some theory and practice to go on. Which causes a lot of the conflict, because German brewing is traditionally different than English and American, so has us on our heads trying to understand what's important and what's not. Does any of that make any difference? Who knows...that's what we're trying to figure out. But it hasn't been the slam dunk I assumed it would be when I started down this path. 2 years into my home brewing I figured 'eh, I can make a nice APA, IPA, brown and dark beers, let's try German lagers'. And some of mine are really nice. But the Helles and Pils are not hitting it.
As was suggested above, grab a 4-pack of PU cans...especially if you can compare it with one of your own light lagers. I agree 'it' isn't a good description for someone who doesn't immediate know what it means.