This month, I'd like to have a good whinge about local bar/cafe owners serving wines by the glass. My girlfriend recently discovered a love of sweet or semi-sweet Moscato, particularly from Italy or Australia. After years of failing to get her to get into wine, this has been a great victory for me. Still, she rarely entertains the idea of drinking wine while out, which leaves me with the option of ordering wine by the glass rather than by the bottle. Unfortunately, I very rarely do this and I'll explain why.
I have a message for local bar/cafe owners: Please don't be stingy and don't serve me wine that has been open for several days or worse. Almost every time I have ordered wine by the glass in Taiwan, it has left me feeling ripped off. So how much wine should you get in your glass? Generally, you should get between 6-7 glasses per 750ml bottle. Fill glasses above waist-high (widest part of the glass)--half-way between the waist and top is usually about right--but leave at least a centimeter or two at the top so it doesn't spill when people swirl the glass to release the aromas. If you wish to serve your wine in larger or smaller glasses than this, then price your glasses and fill them accordingly (generally 125-150ml is about right).
As for serving wine that has been open too long, this is a tough one. Bar owners will reply that not enough people order by the glass, so they open a bottle and often just sell one or two glasses out of it. Hopefully, offering customers better value will help with that problem. You really should be using a decent vacuum seal or spraying inert gas into the top of the bottles and at least keeping them in the refrigerator overnight, and even then only for two days maximum.
These same rules apply for keeping wine at home. Otherwise, you will be drinking wine that has started to oxidise, which means it will taste less fresh and fruity and take on a nutty, sour flavor. Oxidisation is what makes an apple go brown if you leave it after a bite--I doubt you'd like your apple two days later!
Remember when ordering a glass of wine that you shouldn't be buying an old, oxidized one, nor a half-empty one! If you find a place that serves good-value wines by the glass, please support them.