The first glass contains only a very small amount of wine. While this level might be appropriate for a professional tasting where participants sample many wines, it appears insufficient for a typical serving. Most diners would likely feel that the pour is too conservative.
The second glass contains approximately one-third of the bowl. This level provides enough wine for enjoyment while preserving plenty of space for swirling and aroma development. Many wine professionals consider this the ideal balance between functionality and presentation.
The third glass contains noticeably more wine. Although it remains acceptable in many casual settings, the additional volume begins to reduce the available space needed for aeration. Swirling becomes less effective, and aromas may not concentrate as well.
The fourth glass is nearly full. This is the option many people choose instinctively. Yet from a wine-service perspective, it is generally considered incorrect. The wine has little room to breathe, swirling becomes difficult, and the chances of spilling increase significantly.
This often surprises people because it challenges everyday assumptions about value. In many situations, receiving more of something is desirable. Wine is one of the rare cases where moderation can actually improve the experience.
Beyond etiquette, there is a practical reason for proper pouring. Restaurants and wineries want guests to experience the wine exactly as intended. A carefully measured pour allows the aromas, flavors, and textures to work together.
Researchers studying sensory perception have found that smell plays a major role in how humans experience flavor. This means that the empty space in a wine glass contributes directly to the tasting experience. What looks like "missing wine" may actually be enhancing every sip.