Is a eight years old open bottle of brandy good?

It's highly unlikely that an eight-year-old open bottle of brandy is still good. Here's why:

* Oxidation: Once exposed to air, brandy begins to oxidize, which changes its flavor profile and can make it taste stale, flat, or even unpleasant.

* Evaporation: Brandy, like other spirits, will evaporate over time, especially if the bottle isn't tightly sealed. This will weaken the alcohol content and dilute the flavors.

* Quality Degradation: Over time, the complex flavors and aromas of brandy can degrade, becoming less intense and more muted.

Exceptions:

* Fortified wines: Some brandies are actually fortified wines, like Port or Sherry, which can withstand longer periods of time open. However, even these will eventually lose their peak quality.

* Exceptional Storage: If the brandy was stored in a cool, dark, and airtight environment, it might have retained some of its quality. But even then, the taste would likely be noticeably different from a fresh bottle.

Bottom line: It's best to err on the side of caution and not drink an eight-year-old open bottle of brandy. If you have any doubts, it's best to discard it.