Drip Back systems, also known as auto-bac, auto-vac, or Economiser, were once widely used in England and Scotland to recycle cask-conditioned beer that was spilled as it was served by either a beer engine or a Scottish air pressure font. These methods are now rarely used because they are frowned on for hygiene reasons, although some drinkers in Yorkshire, northern England, who demand a thick collar of foam on their beer, defend the system.
To create the head on beer, which has a naturally low level of carbonation, a sparkler is fitted to the spout of the beer engine or font: the sparkler has a tight wire mesh inside it and the beer is agitated as it passes through, forcing carbon dioxide to break out of solution, creating foam. Where a traditional English beer engine and handpump are used, pouring a pint through a sparkler demands some muscular effort by the server because the flow is restricted and the beer is forcefully sprayed into the glass. Some beer inevitably overspills the glass; this is collected in a drip tray and returned to the bulk beer via an injector valve. Today cask beer enthusiasts find the very thought of drip back systems revolting, but they were once quite common. It has often been said that stale beer served through such systems was among the factors that originally led to a decline in the popularity of cask beer in the 1960s and early 1970s.
In recent years these methods have become largely obsolete as a result of the introduction of swan-neck spouts attached to handpumps.
The British brewer Greene King has developed a two-way beer engine: the server can toggle a switch and produce beer with either a thick collar of foam or a smaller head to meet the demands of customers.