Building an Organoleptic Hop Transducer Module


*This article was written for OnTap magazine

It goes by a few different names: Randall the Enamel Animal, the Randalizer, or Organoleptic Hop Transducer Module. Whatever you want to call it, it offers a whole host of experimentation opportunities to a brewer with a level of geeky coolness which can’t be beat.

At its inception, at Dogfish Head Brewery in the U.S., Randall was designed to infuse hops into an IPA during its pour to create a new dimension of hop aroma and flavour in the beer. The Randall was subsequently modified into a two chamber system to try overcome the biggest problem with this contraption – foaming. However, with a few tricks in set up and dispensing, this problem can be easily managed for a single chamber system that is a simple DIY project.

The major advantage of the Randall is the ability to infuse any flavour you want, via hops, spices or fruit into a beer without having to commit a whole batch to the experiment. The added advantage is getting the freshest possible flavour infusion and not having to worry about contamination. The genuine Randall is available to buy from Dogfish Head brewery, but it costs around R3500 before shipping and probable import costs. You can make your own very simply, and with minimal tooling and expertise, for around R400.

The basic principle is to use a water filter housing and replace the water filter cartridge with a custom filter cartridge. The beer flows from a keg into the filter housing, infusing with ingredients as it fills up the housing around the outside of the filter cartridge. The infused beer then filters through the filter cartridge and flows back out of the housing and to the tap. To get more contact time for infusing, the filter cartridge should have inlet holes as far from the housing inlet as possible.

You will need:

1 x Water filter housing

1 x PVC pipe (approximately 300mm)

2 x John Guest / DMfit push fittings

2 x Cistern seals or similar

1 x Filter bag

Beer Hose

Sealing tape

Randall Components
Pool Gobbler sock, PVC pipe, cistern rubber grommets and the water filter housing with DMfit push fittings

Step 1 – Find a suitable housing

The ideal housing for a DIY Randall is a water filter housing. These come in various sizes and configurations which will affect the rest of the build. The housing has 2 parts: the base, which has the inlet and outlet, and the head which attaches from the base by a threaded fitting (with seals). The head of the housing doesn’t need to be clear, but it helps to check that the beer is infusing correctly and the spectacle is a big part of the attraction of this device. The thread size on the inlet/outlet ports varies across manufacturers so be aware of what you are getting since you will need to get fittings to match. Filter housings are available from various water filter suppliers online.

Step 2 – Build the filter cartridge

PVC filter cartridge

The filter cartridge is just a pipe with some holes through which beer can flow, covered by some kind of filtering material so no solids can pass through. Stainless steel is ideal as with all brewing equipment, but PVC pipe will do the job perfectly. The diameter pipe you use can vary depending on the size and shape of the inlet on the filter housing. You need the pipe to seal against the top and bottom of the housing in

a way that separates the inlet from the outlet of the filter housing. Getting the correct length of the pipe will require a little trial and error. Try to get the cuts as straight as possible and remember each end will get a seal. You then need to drill holes in the pipe. Drill 4 x 3mm holes near one end of the pipe, evenly spaced around the circumference of the pipe so that there is an even flow around the filter.

To filter out any solid matter you need some kind of mesh. Muslin or cheesecloth will do the trick if you are able to stitch it into a tube to fit around the pipe. I use the filter bags from a pool gobbler which have a nice fine mesh and are easy to use in this application.

Step 3 – Attach fittings

You will need to get the correct fitting to match the inlet and outlet of your housing. You can either use push fittings (John Guest or DMfit) or barb fittings. Either will work, it just depends on the availability of fittings you find to match your housing.

Attach your fittings to the housing making sure to use sealant tape on the threads to that you have a sealed fit.

Step 4 – Setting up

Place the seals in your filter housing, cover the PVC pipe with the filter bag, and insert the pipe into the head of the housing, making sure it is oriented so the holes sit a maximum distance from the inlet and outlet. Fill the filter head (on the outside of the pipe) with your infusion ingredients and attach the base. Make sure it is tightly sealed. Connect a beer line between the inlet of the housing and your keg coupler (or connector). Connect another beer line between the outlet of the housing and the tap.

For a jockey box set up using a chill plate or coil, connect the cooling element between the Randall and the tap so that beer is cooled after infusing. The flavours will infuse better at warmer temps and the beer will reach the tap nice and cold.

Randall Complete


  1. Try all sorts of flavour infusions. I’ve used hop pellets and cones, fruit, coffee and spices to great effect. I’ve also split the beer line from the keg and run a single beer through 2 separate Randalls carrying different infusions as shown below.
  2. Foaming can be a problem with some infusions. Try serve at a low pressure with the flow restrictor on your tap at ‘full-open’. Slowly increase the pressure to try find a sweet spot. I have a fairly long beer line coming out of my chill plate for added resistance which helps as well.
  3. Be careful to orient your pipe filter cartridge properly. More contact time in the Randall makes a difference, and you can’t easily change the orientation once you have begun dispensing.

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