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Brewer & Distiller International Article

An article in October’s edition of the Brewer & Distiller International magazine explored the manufacture of plastic casks and kegs, with GPS being featured throughout. The article details the history of GPS and the obstacles we faced to bring a successful plastic cask to market. You can read the article in full below.

New Keg on the Block
Is plastic the answer to losses?

By now you will probably have been alerted to a brand new plastic keg from Global Polymer Solutions. You may even be one of the hundreds of brewers worldwide who have been using its nine gallon casks. The UK based company has worked hard trying to establish the Green Cask and Green Keg as a reputable and reliable brand.

The project has been long in gestation as seemingly no brewer wanted to be first and a couple of manufacturing partners went bust before GPS targeted the burgeoning UK micro-brewery market to build up confidence in a plastic cask that did not leak and can be dropped full and under pressure from the top of a fork lift mast - but hopefully not too often.

Plastic casks were not new. There were many stories of problems with the integrity of a three piece (two ends and a belly) injection moulded unit which was welded together in a post-moulding operation which unfortunately made the joints rather brittle just at the point you want a cask to be strong. The use of two identical ends led to many tales of hapless cellar men trying to tap the blanked-off keystone in the back head! Knowing little about plastic technology, brewers were happy to believe that a blow-moulded unit would be no better.

British Grit

So this is a story of true British grit in tackling every single objection to the use of a polymer material that any brewer could possibly throw up. Today production is under the control of ISO9000 and the factories under environmental standard ISO14000. Testing is rigorous with a three-hourly destruction test to check material thickness at seven crucial points plus a pressure retention test and a 2m drop, full and under pressure. Happily the spent sampling material is ground up and returned to the input mix.

I admitted to some similar scepticism when I arrived at the first part of the manufacturing process at Alliance Moulding Services near Rochdale where Jim Kelly is MD and makes the injection moulded rolling rings and the new screw in shives for the casks. For the new keg, Jim is manufacturing the top and bottom chimb sleeve which encapsulates a blow-moulded single aperture bottle for the keg. The chimb pieces interlock around the belly and are secured in place by two rolling rings, made from a technical polyurethane rubber, with a central collar between them. There is no glue, no heat welding and the carefully designed gaps in the structure ensure that any shocks can be absorbed without damage. These sections are then transported 20-odd miles north to GPS's blow-moulding plant based at the Weltonhurt factory at Blackburn to mate up with the blow-moulded main container sections.

Global Polymer Solutions was started in response to Greg Whitehorne's search for a plastic cask and keg design that could meet the requirements of the brewing industry. The keg and cask were designed around the blow-moulding process which provides the core strength of the containers. Greg, now badged Sales Director, is a Sheffield lad. School prepared him for a career down the Yorkshire coal mines but in a long and tortuous story he ended up as a time-served joiner, builder, property developer and service station designer and builder.

Inexorable Losses

He had renovated pubs for Bass North and was enticed into a Yorkshire beer wholesale business called Last Orders. Although selling beer did not last long, his exposure to that and the pub business got him thinking about the seemingly inexorable losses of stainless-steel kegs. Back in 2005, Carlsberg, as one of his largest suppliers, was working up a system to introduce deposits on containers. Whitehorne surmised that this would not stop the theft but merely transfer the responsibility of care to someone else and move the cost down the line. In the end, the UK brewers could not agree on an all-encompassing system and it was left to some individual companies to launch their own schemes.

As we all know the problem is the value of scrap stainless-steel. Add to that an underworld of merchants where the unscrupulous can render the material anonymous easily and pass it quickly into larger bulk recovery operations which ultimately source the hungry blast furnaces of the Far East. So, if the container had no recycling value (but was recyclable), no one would steal it. A simple concept, but the start of many tribulations.

According to Kegwatch, which repatriates kegs to their owners and works closely with the police to track down thefts both small and large, annual losses totalled £40 million a year before the economic recession took hold in 2008. This caused a slump in scrap prices, but it did not take long for them to rise again and annual losses are estimated still to be in the order of 8% per annum. A figure echoed by Diageo and other brand owners across the world. People will always want plant tubs, car park markers and mooring buoys for their yachts and they do get dented and damaged, so some attrition is inevitable but even if that is 1 %, the annual cost reduces considerably. Going to China is not really a solution to getting the costs down as even if the quality is tip-top, they are still steel and will still get stolen.

Thirty Percent Less

Now consider the fact that a plastic keg will cost some 30% less than the same size in stainless so that replacing the residual losses will cost less and the price will allow start-up brewers to build up a fleet more cheaply. Heather Ales in Scotland together with many other UK-based brewers have bought GPS units for a foray into the export markets and they know that eventually they will all come back. GPS has, with Ken Simpson of Spears Limited, developed a plastic spear for the keg range, incorporating tamper evidence and safety features that will protect the end user from over pressurising the keg. It will also be less than half the cost.

Plastic is quieter to use and quieter to make; there is a quiet hum in the blow-moulding factory compared to the continuous clatter at stainless cask and keg makers. They are quieter on the racking line and delivery restrictions on certain pubs could be lifted if everyone went plastic. Plastic does not dent so brim fillers will have no capacity problems.

There are branding opportunities through different colours of material. You can have black, orange, red, silver, bronze, green or blue and the rolling rings come in a multitude of colours. You can have a printed vinyl strip wrapped around the belly for brewery name or ownership coded coloured bands. These latter are fixed with marine-grade gum and are waterproof up to a point dictated by your cask washer and external scrubbing. It’s best to replace them annually at a cost of £2. The brewery name is embossed on the head by putting an incised plate into the blowing mould. Container numbers were originally cut into the cask near the shive hole but in the future, GPS hope to laser-print on to the head where it will be easier to see.

Plastic casks are 50% lighter than their steel counterparts. I have heard some grumbles that such casks move when you try to tap them but that is surely an issue about how much wellie you apply to the operation. Savings accrue during transportation; loose in a Transit van you can get eight more casks in before going over the weight limit. Whitehorne spoke to brewers for a full eighteen months. Colin McCrorie, then with Coors, was particularly helpful in test filling, performing taste tests and stress testing from different heights and different angles. GPS consider the life expectation of the cask and keg to be in the order of ten years. This is based upon the experience of long term storage and handling of aggressive chemicals in containers made from identical polymers.

Leaks Through the Shive

Brewers indicated that poor control of fermentable residue and long distances to wholesalers without refrigerated transport led to leaks through the shive on the traditional plastic casks as they were only rated at half a bar internal pressure. GPS looked at the worst case and demanded two bar. The weakest point will always be the shive aperture which they set about beefing up. For full pressure they use a screw in polyurethane insert which is secured by a large hexagonal section allen key. Cellar operations are then as normal.

You can use a torque wrench to tighten but I was told that operators quickly get used to the inserting and tightening. "You are not doing up a lorry wheel" observed Greg. GPS is working with machine suppliers to adapt the usual shive inserters on the few existing automatic cask lines where the plastic cask is identified and the tool turns to offer up a screw applicator instead of the usual piston pusher.

You can still have a hammer-in shive hole if you like, but the cask will not withstand two bar. The shive hole will always be the weakest part of any plastic cask and a lot of engineering know-how has gone into the shape and thickness around it to direct forces and keep pressures even and then to ensure two bar can be held. The screw aperture is strengthened by a stainless steel ring which is heat sealed around it. Currently the screw in shive costs 20p, more than a micro brewer's price for a plastic shive of around 16p but GPS are working to increase production and are working on a new jig to make them four at a time to accelerate production from 180 to 700 an hour which will make the cost more competitive. If you use vertical dispense which is popular in the Scottish trade, the shive can be removed for washing, soaked in sterilant and reused.

GPS Cask Supply

GPS have supplied over 45,000 casks to the trade. Most are in the UK and all the examples I saw at Blackburn were for breweries I had never heard of, showing how vibrant the current industry is. Some have been exported to Europe, Australia and New Zealand and the States where GPS has an agreement with Allied Beverage Tanks of Chicago which offers a turnkey brewery build from 15 to 30bbl and will be offering the GPS range of kegs as well. GPS now sits on the BFBi Cask and Keg Committee and follows all the guidelines laid down by them for manufacturing specifications. Assessment of plastic taint into beer and cider as well as migration of beer into plastic has been completed by PIRA (now by holding the product for ten weeks in container.

The casks and kegs are made of tried and tested (over forty years) Total Petrochemicals polymer which is a high-molecular-weight high-density food-grade polyethylene (HDPE fluff resin TP 56020S to be precise). Colour and UV stabiliser is blended into the HDPE powder from large silos to a hopper above the moulding machine. UV protect ion is essential as you do not want your first batch to fade in the sun and then not be the same colour as subsequent deliveries.

The material is heated to 220 degrees Celsius and extruded into a sock (parison) via a circular die, about 150mm in diameter. The parison thickness is varied as it is extruded in order to get the best possible wall thickness distribution. The two mould halves clamp shut around the parison and air is applied to blow the container to shape.

More Sophisticated

For kegs it is a single aperture bottle but casks are more sophisticated. The blow tube projects through the keystone hole and the thick walled sock is pushed into the chimb cavities and blown out against the inside of the mould to form the heads and wall. The cask needs to be held for around eight minutes in the mould to start to set before being released. The top and bottom remains of the sock are cut off and the still-hot casks placed on a table to be air-pressurised to ensure the cooled volume is exactly 40.6 litres.

Around ten casks per hour are produced on Weltonhurst's VK 200 machine. This figure could be increased by using post moulding cooling jigs. The cool casks then have the shive hole drilled out and two angled drain-holes drilled so casks can be washed properly. The keystone housing is precisely machined out to accept the No.2 plug. A sharp knife is now used to tidy up the exterior and a blowtorch neatens the finish. Finally the inside is hoovered out to remove last traces of swarf.


Next stop is finishing where the steel shive-strengthening ring is hammered on and heat-sealed in place. The rolling rings are kept pliable in a hot-water bath and are hammered in to place. These are 12mm thick on top of the cask plastic at another 8mm. A steel keg has only the metal thickness at this point and rolling on a road surface does create abrasion which can lead to pin pricks. The cask number is cut and any banding applied before loading 32 to a pallet with heat shrink wrapping to secure the load.

Transport is then arranged depending on the contract agreed. A 4.5 gallon pin cask is on the drawing board. There is unlikely to be sufficient interest in larger sizes as you would need at least 20,000 units a year to cover the cost of tooling set up but I saw 200 litre sulphuric acid drums being made so larger casks are possible. The 50 litre keg will soon be joined by a squat 30 litre keg and a tall 20 litre keg (like a US sixth barrel).

Alliance in Rochdale has 21 employees working 24/7. Weltonhurst is a lot bigger with 120 staff working around the clock. Twenty one blow-moulding machines make all sorts from water butts, watering cans, home brew vessels, supermarket cages, road barriers and collapsible bollards to floating harbours for the military. So there is lots of capacity for the big push into plastic kegs.

Article by Roger Putman

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