Hold the glass under the tap or bottle and tilt at a slight angle, so that the liquid hits the side of the glass before reaching the bottom. The purpose of this is to prevent an excessive build up of froth, which will otherwise fill the glass.
Froth on top of beer, the size of the head, is a big bone of contention in pubs in the United Kingdom.
If the pint has a large head, it should be left to settle, and the glass topped up to give a full pint. Bar staff should always respect a request for a top up when the glass has not been touched.
The weights and measures act defines the quantities in which beer can be served and sold in a public house. Unlike most other UK measures, these are the imperial measures of pint and half pint.
A pint glass must either hold more than a pint, and have a line indicating the pint, or hold a pint when full to the brim (both kinds of glass carry a pint crown mark). Unfortunately most pub owning companies including breweries prefer the latter. Sadly, this leads to short measure for the beer drinkers, with punters being served with less than 95% liquid.
The law allows a 'reasonable head' to make up part of the measured pint. it doesn't define reasonable though, which is why requests for top-ups should be honoured.1
There is also a regional discrepancy in the UK, with Northerners preferring beer with a head, and Southerners wanting a full pint of liquid. Lined glasses would keep both kinds of drinker happy.
The Labour Government is behind on some of its election manifesto promises in this area (probably due to some business vested interests), and the Campaign for Real Ale is currently fighting a campaign against short measure.
Also, there are special requirements for pouring a
bottle conditioned beer. These require avoiding shaking up the
sediment before starting to pour, pouring the beer slowly, watching the sediment to make sure little or none of it leaves the bottle. Again you want to tilt the glass, to avoid the build up of froth (which can easily fill the glass if you get it wrong).
Update:
Having bought a bottle of Coopers Sparkling Ale, it seems that it is a matter of personal preference whether to drink the sediment, or leave it behind in the bottle.
From the label:
Coopers Sparkling Ale is brewed using the centuries old top fermentation method. Resulting in a characteristic fine sediment forming on the base of the bottle. This sediment is completely natural and can be gently mixed before drinking or poured carefully leaving the sediment in the bottle.
In terms of any nutritional value,
microbiologists will tell you that a live beer, such as a draught
real ale or a
bottle conditioned beer contains yeast in solution, much as a
live yoghurt contains the
acidophilus organism. The sediment is actually dead yeast cells.
In particular, people with a yeast allergy or candida, should avoid drinking sediment - and should probably avoid real ale altogether.
1 Thanks are due to ascorbic for this contribution.