Such as Port, Sherry, Sauternes, etc., due to the high alcohol content or high sweetness, usually as a post-dinner wine or a small drink, the pouring amount is the smallest, the standard amount is usually between 2-4 ounces (60-120 ml), 3 ounces (75 ml) is a common number. The higher alcohol content is the main reason.
In order to allow participants to try a variety of wines without overdosing, the amount of wine poured at a tasting is very small, usually between 1-3 ounces (30-90 ml), with 1-1.5 ounces or 2-3 ounces being common. Professional tastings may even be as small as 30 ml (about 1 ounce), and spitting is encouraged.