Keeping your glassware 'beer-clean' is key to serving the perfect draught.
If you have overhead glass racks, use them for liquor and cocktail glasses. These drinks are not affected the same way as draught beer.
A beer-clean glass will shed water evenly in unbroken “sheets”. On a glass with invisible film, water will break up and form droplets on the surface of the glass.
In a beer-clean glass, salt sprinkled on the interior of a wet glass will adhere evenly. If not properly cleaned, salt will fall to the bottom or adhere in a random pattern. Salt will not stick wherever a greasy film is present.
A beer-clean glass will form a thick, tightly-knit, creamy head. The beer will be sparkling-clear and free of bubbles. A glass that’s not properly cleaned will have loose, large bubbles (fish eyes) that will cause the head to disappear within 10-60 seconds. Bubbles will visibly rise from the bottom of the glass and adhere to the sides.
In a beer-clean glass, foam will adhere to the inside, forming a parallel ring pattern (lacing) as each sip of beer is taken. In a glass that is not properly cleaned, foam (if there is any) will adhere to the glass in a loose, random pattern – or may not adhere at all.