Finer Points - Sparkle & Sediment
Typical commercial practice is to sterilise before filtering, carbonating and bottling. Traditional keg ciders, however, are unsterilised and still; sediment accumulates at the base of the keg, below the tap.
Bottle conditioning is the old fashioned, or traditional method, of producing a sparkling drink, where a small proportion of fermentation occurs within the bottle. This results in a both a finer sparkle (smaller more refined bubbles) and a light sediment (at base if stored upright). This can be collected on the cork (with careful regular turning) and removed completely by freezing - quite a skilled manual process (hence the price of Champagne).
My preference is for the finest of sparkle - a mere prickle. A gentle hiss on opening and a mysterious, rising mist aids anticipation. A fine sediment on the base can be a sign of a natural product, but if too lively this will inevitably get disturbed (unattractive). Carbonated products, while consistent, are often somewhat fizzy, full of large coarse bubbles. Look for very fine streams of small bubbles (playing against the glass) as a sign of a carefully bottle conditioned drink.