Beer bubbles have a unique structure which affects the flavour of the beer. A good head of foam shows that the beer is fresh and carbonated, and allows aromas to develop.
The perfect poor ensures the beer's flavour is at its best. Here is how to do it:

1. Hold the beer glass at a 45 degree angle, 10-20mm above the top of the glass
2. Make sure the glass is not touching the tap
3. Once the glass is halfway full (50 percent), tilt it back to the upright position at 90 degrees
4. Poor the remaining beer, ensuring a 10-20mm head of foam