Cooking sherry or any cooking wine for that matter is already bad by design when you buy it: Only the worst wines that can't be legally sold as sherry or drinking wine are used to make cooking wine as a way to still make big bucks on these defective products that would be used for vinegar otherwise.
Cooking wines have salt and a bunch of other flavorings or chemicals and whatnot added, but that does not prevent them from spoiling. It probably has to do more with the fact that cooking sherry is the least fruity sherry, and is therefore less likely to keep for long, although this can be prevented by adding more sugar if it is sherry.
It does not turn "bad" though, it just turns into vinegar and after it is fully turned into vinegar in a few months, it can be used in French dressing, to deglaze fried onions or gravy, to marinate meat, etc.
It will still be a low quality vinegar, because garbage in, garbage out and that sort of things, but not a total waste.
Sherry vinegar is a much sought after product. Quality sherry vinegars sell between $15 and $30 a bottle, depending on their age and origin (search for Banyuls vinegar for instance.)
Anything can go bad if left uncooled or old. I can never make port wine cheese last long enough to go bad.
After a while, white wine can deteriorate in quality.
Port is a wine made in a specific manner.
The introduction of the port wine which is a sweet fortified wine from the Douro region of Portugal.
wine
Wine vinegar does not contain any wine and cannot go bad.
It's a desert wine.
yeast
port-wine stainport-wine stain
A port wine glass looks like a normal wine glass except the inside is a bit bigger than normal. The port wine glass has a thin stand with a wide circular shape.
Yes the speaker port can and often does quit working.
Cognac is an aged distilled wine which tastes nothing like port.