Prolonged chilling and filtering
By holding beer at a temperature of 26º to 28º F for one to three weeks, more material was precipitated out than by the quick method. Resulting in a beer which would remain free from sediment for several weeks after bottling. The downside was that the process made beers taste thinner and weaker than a cask version.
Prior to chilling, the beer was dry hopped and allowed to condition in the cask. In contrast to beer for bottle-conditioning, a high level of CO2 was desirable. Some brewers used Kräusen to condition in the cask, but most preferred priming sugar.
Some brewers added additional CO2 before filtering, while others pressurised casks with CO2 while they were in the cold store.
Despite the limited shelf-life of non-naturally conditioned beer, brewers in the UK almost never pasteurised their beer. The only exception being Lager.
UK brewers associated the practice with Lager beer and didn’t find it appropriate for native types of beer. Why was Lager almost always pasteurised? Because it was susceptible to heat when unpasteurised. At least that’s what British brewers thought.
It was recognised that the shelf-life of beer was improved by pasteurisation, but this was outweighed by its disadvantages. The greatest being the “bready” flavour it gave to beer. Which wasn’t popular with everyone:
“Its general tendency is towards a loss of delicacy, and it is strongly objected to by some beer drinkers.”
Pasteurisation also required extra equipment, so a capital cost. If you were already producing beer which kept long enough for your local market, why spend money for little practical gain?