What is "dumb phase"?

[WileECoyote]

dumb; dumb phase
Though the term dumb is sometimes used as a synonym for CLOSED, it really has a more complex meaning. The dumb phase of a wine (generally red) is that period of transition from its youth to maturity. Shortly after bottling, a wine may be luscious, with rich, ripe aromas and flavors. However, after a certain period of time (usually several months), such a wine may begin to close down-the fruit begins to decrease before the complexities of maturity have fully developed. The combination of declining fruit and pre-emergent complexity cancel each other out, creating a wine that simply doesn't taste very good. VINTNERS have no idea what causes this phenomenon but do agree that the time frame for this dumb phase, which can last for several years, is completely unpredictable. The dumb phase of a wine is also referred to as the flat spot or the awkward, transformational, or adolescent phase.

Source:http://www.epicurious.com/drinking/wine_dictionary/entry?id=6295