As we've gone back and fourth, one bit of literature she sent me was a piece explaining in some detail the Goldcapsule designation. As it's both interesting and not necessarily immediately obvious, I thought it would make sense to post it here in full:
Understanding “Goldcapsule”
In an effort to simplify the universal marketing of German wines, the government stepped in and revised the Prädikat system to allow for only one Auslese category. The new rule was met with frustration by the high-quality-conscious winemakers, mostly those from the Mosel, who had perfected the art of selective harvesting and now were deprived of the traditional means to express the different levels. The issue with Auslese in particular is that it is the Prädikat level with the widest Oechsle range (in Germany, the natural concentration of the grape juice at harvest is measured in degrees Oechsle). On one end of the spectrum is a style closer to Spätlese and on the other end is Beerenauslese. So with just Auslese on the label how would a customer know if it was closer to Spätlese style or more close coming to a BA? Since the 1971 law forbid use of wording to denote special bottling within a Prädikat, estates got around that by developing other means of identification.
The most acknowledged method – and the one also used by Joh. Jos. Prüm estate - is a golden capsule, in contrast to the white capsule used for the “basic” Auslese. A short gold capsule usually means a presence of botrytis and a long gold capsule represents a remarkably higher percentage of botrytis and consequently concentration, close in quality and style to a Beerenauslese.
Unfortunately, there was no uniform solution by all estates found after the change of law in 1971. Instead of the Goldcapsule, some estates opted to use a star system on the label and still others use a cask number. Also, there are some wineries that use golden colored capsules on all their wines, and there are again others that produce Goldcaps not only in the Auslese but also in the Spätlese category..
Now, what are the characteristics of a Goldcapsule, why buy such a wine? Think of them as limited edition, rather small production lots of the best Auslese of a vintage. They are made from stronger selected grapes containing higher concentrated juice, usually affected by a certain amount of botrytis / noble rot, capable of aging even remarkably longer than “basic” Auslesen, lasting for many decades. In the course of time, they lose some of their sweetness, gain more and more elegance and harmony and the complex profile and depth come to the forefront.
Goldcapsules are not made every year. Due to an overall higher ripeness of the grapes in the more recent past, there were more chances to produce such wines than in earlier days, however, for instance, vintage 2004 allowed only a very small quantity to be produced which was only offered at the VDP Mosel auction in Trier.
To differentiate between Goldcapsule and Long Goldcapsule, Joh. Jos. Prüm estate marks the Long Goldcapsules with two white stripes at the bottom (see right bottle) in contrast to only one stripe for the Gold Capsule ( left bottle):