Signs of Poor Storage
Poor storage conditions for bottles of wine are not easy to determine by merely looking at the bottle, but occasionally there is a clue. The first and most obvious bit of evidence is leakage.
When bottles are placed in storage where temperatures rise and fall, the cork may push in and out of the bottle enough to permit the wine to leak through. Check the capsule carefully for evidence of moisture. Sometimes a bottle leaks and a stain may be found on the outside of the bottle, or on the label.
Also, check the cork underneath the capsule. Place a finger on the top of the capsule. If the cork has moved up and is pressing against the capsule, higher than the lip of the bottle, fluctuating temperatures may have caused the cork to move up.
However, leaking bottles are not always a sign of bad storage. Many sweet wines seem to leak even in good storage. I have had a number of Sauternes from perfect storage conditions that tasted fine even though there clearly had been leakage.