‘Corked’ has a specific meaning - it is used of a wine which has been tainted by a fungus found inside cork bark. This can happen to any bottle sealed with a natural cork, no matter how expensive. There is no definitive test you can do at home, but you can learn to spot corked wine by its aroma and flavour. Its effects range from mild (the fruit flavour of the wine is dull and muted) to severe (the wine has a strong musty or rotting cardboard aroma). If you are unsure whether what you can taste is cork taint, it helps if you can compare it with the aroma and flavour of another bottle of the same wine. It would be very unusual for both to be corked, so if they taste the same there may not be a fault. You cannot tell if a wine is corked from the cork itself. A crumbly or mouldy cork does not mean that there is anything wrong with the wine.