Lesson 2 - Wort Clarification Technology and Process Control
This lesson compares the design and operation of different wort clarification systems. It provides you with the information to help you justify why you would choose one method over another.
Hop Back
There are a several versions of hop back in use today. The original version is still used in UK breweries who use whole hops. It is very similar to a mash tun in that it has a false floor usually made of punched plate with circular holes and in some cases slotted plates or wedge wire.
The vessel is usually very broad to provide a large area for filtration. Height to width ratios of 1:1.5-2 are common. The vessel is filled from the top via a spreader that distributes the wort and hops evenly over the false floor. The wort is usually left to stand for a period to allow the hops to sink and then the wort is recirculated through the false floor to clarify it and establish the filter bed. Wort must be run relatively slowly from the vessel to prevent compaction of the hop filter bed. Casting out from hop backs typically takes an hour in large versions. The filtration provided by the hops is very effective and brilliantly clear worts can be produced.
Hops can be added to the hop back before filling to add late hop character to the beer. Other flavourings like orange peel and spices can also be used. Some vessels have a sparging facility that showers the spent hops with water to flush out the residual extract. Some brewers do not sparge the hops to prevent leaching out bitter or astringent material from the hop cones. Spent hops can contain as much as 0.5 kg/L of extract. Some also collect the wort produced by sparging and use it to mash a subsequent brew.
To use a hop back almost all of the hop grist must be whole hops. A small proportion can be pellets or extract but there needs to be enough whole hops to act as a filter.
Figure: A traditional British hop back
A more modern version of the hop back is used after a whirlpool to add whole hop character to worts produced using other hop products. These vessels are typically smaller in size and in some versions a cylindrical sieve made of punched plate or mesh holds the hops as the wort flows through them. Some have a central slotted candle filter and other versions have false floors. This version of the hop back can also be used to add suitably sized spices and fruit peels. The figure below shows a small scale example.
Figure: Craft hop back