Bad habit many bartenders possess. If the glass touches the faucet, they cannot see the flow. If the flow is not clear they need to stop, pour out the foam and start fresh with clear beer. It is impossible to pour clear beer on top of foam.
Also, in a bar, if the bartender refilled a patrons same glass, would you order a glass of draught there? You wonder how many cold & flu strains have been passed along by contaminating the faucet.
Scott Zuhse, Instructor
Micro Matic Dispense Institute