The question how to judge the quality is difficult to answer. For every (non-professional wine) person tastes a little bit different, everyone will describe a wine a bit different.
The first step therefore is to find a description of the wine. The sum of the answers provides a basis to the judgement of its quality:
One single negative fact can ruin an otherwise good wine: it might be perfect in fruitiness and all other ways, but a taste of bitterness or another flaw annoys the taste so very negatively that the wine has to be considered as faulty.
Look at the wine, hold the glass against the light:
Sniff the wine’s smell, swirling it slowly in the glass. Is the smell
Try to name every single touch of a smell, even if you do not expect it in a wine.
Taste the wine slurping. A noisy savouring is the best, to catch some air together with the wine. The air supports the taste buds for better tasting. Let the wine roll over the tongue so that all taste buds together are involved in the tasting.
Taste in a group: Everybody’s taste is very individual, that’s why everybody describes a wine a little different. Communicate what you taste with others and compare.
This question is also one referring to individual preferences. Some people have trouble when drinking wines of high acidity. It might cause them an unpleasant feeling in the stomach or even a heavy heartburn.
Another problem might be defect wines. Unfortunately people will find here and there defient wines, especially in the low-price category. People will easily find out if a wine is good or not tasting it. It should never taste of
German quality wines are checked by authorities in an official wine quality control after bottling. Only wines which passed this control successfully are allowed to be named “German quality wine” or “German quality wine with special distinction”. These wines bear a quality control number (AP-number) on the labels. It makes the wine trackable, for the authorities keep 2 control bottles of each.