Never had that problem. I’d say a couple weeks.

Lot of room in “good”. What I would find acceptable and you might not is as variable as the wines themselves. Then again different wines degrade faster than others. Rieslings hold up really well due to all that sugar. It’s the reds that head South in a hurry. And one of those cheap hand pumps to evacuate the air from a resealed bottle is well worth the investment.

When you are done drinking it for the night, be sure to cork it again. It will stay better longer if the exposure to air is limited.

I did pump out the air and recork it. I opened it for a group who didn’t drink any and I have another group coming in a few weeks.

I’d use it in cooking and have a new bottle for the new guests. Or, I’d warn them it’s been open, and ask if anyone wants to be the guinea pig and try a taste to see if it’s not vinegar.

Or, no wine available. If you come to my house there is a good chance there is no wine or beer around. Depends on why you are coming over.

Did you guzzle a little yourself for reference against the next time you open it?

@stanleybmanly I didn’t but I could.

I would not serve to guests wine that has been open for weeks even if it had been in the refrigerator. I might go a couple of days but that’s it..

If you and a friend are a little adventurous you can experiment and have a wine tasting where you try it over time, That would be fun and informative.

I think “a few weeks” would be too long to hold it. In my experience (limited, to be sure) it gets more bitter after it’s been opened.
I have no idea about the air-sucking thing.
Maybe keep it and try it before they come over, but have an unopened bottle to hand in case you need it.

A few days is about it. You can push it to a week, but it’s not going to be great after 5 days. I would not serve an opened bottle after a week. Maybe you could distill it into brandy?

^^^^ @gorillapaws Better to let it age into vinegar for a fancy salad dressing!