Ullage refers to the loss of wine from the bottle by evaporation or leakage. Evaporation is a perfectly natural effect, whereas leakage is less desirable but is almost inevitable with age.
The following chart lists the common interpretations of ullage levels.
Print it out onto A4 paper (or preferably card) and it should be the correct size to be
cut out and used as a template to fit over your bottles.
Into Neck : Can be an original low level of fill. Quite acceptable for any age of wine. Exceptionally good for wines over 10 years of age.
Top Shoulder : Still quite acceptable. Normal for wines between 10-20 years.
Mid Shoulder : Probably due to some slackening of the cork and possibly some signs of seepage, it is not abnormal for wines of 30-40 years of age.
Mid to Low Shoulder : Starting to become risky. There should either be obvious signs of seepage, or the wine may have been stored in less than ideal conditions over the years.
Low or Bottom Shoulder : Will by now probably be undrinkable due to the excessive air in the bottle oxidising the wine.