We’ve all been there. You’re not sure whether or not to open that “good” bottle of wine because you might not be able to finish it fast enough (psh, amateur).
Oxygen and wine are in a lusty short-term relationship. Wine needs small amounts of oxygen to aerate and release its aromas, but the long-term relationship thing just isn’t happening. Too much exposure turns wine rancid. Sticking the cork back in the bottle limits the amount of oxygen coming in contact with the wine, but as you’re probably aware, this doesn’t guarantee the bottle a delicious eternal life.
In general, red wines have more endurance than whites in respect to time. The best casual option, for white or red wines, is to stick the cork back in the bottle and stash it in the refrigerator. Cooler temperatures help slow the oxidation process. Wine preservation spray (available for a few bucks at your local wine store) and champagne bottle stoppers definitely help keep wine fresh, and they're worth buying if you tend to leisurely enjoy bottles over the course of a few days.
Red wines will generally keep longer than white wines because of their tannins. The structural elements of tannins help prevent oxidation in wine. That being said, the lighter the red wine (think Beaujolais or pinot noir), the faster it will spoil: keep heavier reds up to five days and lighter-bodied reds up to three days.
The same applies to white. However, a fuller-bodied white like chardonnay will tend to last longer than a lighter style like sauvignon blanc. Think about it this way, flavors and aromas of oak in a heavier white would stay present longer than fruity or floral whites that are specifically enjoyed for their freshness. Fresh fruit and floral notes tend to fade quicker.
Unless you have a proper stopper, sparkling wines must be drunk within four hours of opening. Keep bubbly bottles up to a full day with one of these.
Things to consider:
Red or whites with a higher alcohol content will probably buy you a bit more time.
A bottle ¾ of the way full and four days old could be totally fine for drinking, whereas a bottle opened for the same amount of time with only half a glass left is probably not worth it. Surface area.
Also, wines over 10 years old should be drunk within 24 hours or less of opening.
Will old wine make you sick? No, but it certainly won't taste good.