Xymo’s purpose is to make it easy to brew great beer by ensuring a perfect fermentation. With so much emphasis on monitoring and control, we had some unique considerations for Xymo’s fermentation vessel, such as:
- Thermal Conductivity – We want to control the temperature inside our fermentor in the most convenient way possible (for the brewer) and by keeping our cooling apparatus completely external to the fermenter, there are no extra parts in contact with the wort that need to be cleaned and sanitised. Stainless steel is our favourite choice of material because it has decent thermal conductivity and a lot of desirable properties for brewing and longevity. Glass would be great too, but we steered away from it because it rately has a perfectly uniform shape, it breaks easily and can be dangerous, and also because it’s a poor thermal conductor that wouldn’t work well with our design.
- Overall shape – With the aim of attaching an external heater/cooler, thermal efficiency is important and we were looking for a fermentation vessel with walls that we could easily affix a thermal transfer plate onto, that would also fit easily into an insulating thermal jacket. With the expectation that our fermenter wasn’t going to have any flat sides (because corners are bad for fermenting and cleaning), we wanted a vessel that would at least be cylindrical. Unfortunately, many of the existing fermenters on the market actually have a very slight conical and oval shape to their walls and this would necessitate costly CNC work to fabricate a mounting plate that would fit. Legs were also a disadvantage because they would complicate the fabrication of a fitted insulating jacket.
- Sensor attachment – In order to support the sanitary attachment of an airlock and sensors, we needed a fermentation vessel with modular mounting holes. The “gas in” and “beer out” posts of a standard corny keg were a tempting compromise, but they’re just a little small for a blow-off tube connection and many brewers report that they are easily clogged. Also if we wanted to fit sensors in there they would have to be extremely tiny. Some customisations will be necessary if we are going to use a corny keg.
- Sufficient volume – Speaking of corny kegs, while plenty of home brewers ferment in corny kegs, it is very limiting for the batch size that can be produced. If our ultimate goal is to serve from a 19 litre keg, then our fermentation vessel has to be at least a few litres larger to account for trub and krausen. A quick email to A.E.B confirmed that they can’t produce large corny kegs (>19litres) on their current factory line so I’d have to find my own supplier.
- Air tight – Some time ago I imported a number of Chinese kegs that were anything but airtight. The lids were warped and didn’t seal unless the clamping ring was done up extremely tight with a large spanner. Since this unfortunate purchase I’ve come to respect the importance of a good sealing fermenter design. In order to support natural carbonation and pressurised transfers, Xymo needs a reliable lid seal that works.
- Easy cleaning – Fermentation is messy, so for most home brewers, the ability to “reach inside” a fermenter for cleaning is considered mandatory. Unfortunately, this requirement rules out using the “commercial” style kegs as a fermentor because they only have a small opening for a Micromatic spear or similar. This is a shame because commercial style kegs are a huge market, produced by the tens of thousands and a fermentor based on these kegs might benefit from the existing economies of scale.
- Shippable – We want Xymo to be a “global” product that we can ship direct to our customers all over the world. The trouble of course is that the shipping for a single fermentor can range from “ludicrous” to “highway robbery” depending on your choice of shipping carrier. That’s why it is important that shipping weight (including volumetric weight) is a strong consideration in our product right from the outset.
So with these goals in mind we set about sourcing a fermentation vessel that we could customise for Xymo’s needs. Not surprisingly, many of our design criteria immediately steered us towards kegs because they’re reliable, strong, affordable and designed for efficient shipping. Furthermore, the “corny” style kegs have a removable lid that allows you to reach inside for cleaning. We just needed a corny keg with a large enough volume for single batch brewing, some nuts welded to the side so we can mount our cooler and to exchange the keg posts for a more universal type of fitting that could support our sensors.
The moment we landed in China we started organising to have some samples shipped from various manufacturers around the country. A lot of our contacts appeared to sell the same products and it was a little time consuming to separate the manufacturers from the distributors, but a few simple questions about customisations and most of the distributors quickly lost interest. Three kegs arrived ranging from 19 litres to 25 litres and each had very different manufacturing techniques.
19 litre keg
This keg was the smallest of the three and although I was looking for a 25 litre keg, this 19 litre version was sent because it’s all the manufacturer had in stock at the time. The manufacturer assured me that they can also produce a larger 25 litre version of the same keg and that the diameter will be the same. This way I can still evaluate their build quality and move forward with our jacket and heatsink designs, knowing that it will all fit the O.D of their 25 litre keg later when it becomes available.
|Construction:||Seam welded. Bottom is domed outwards. Rubber base added for stability. One comfortable handle. Feels solid and heavy for its size.|
|Surface Finish:||Pickled and passivated leaving a smooth matte grey finish.|
|Weld quality:||Seam welds are slightly raised but smooth to touch. Most welds are great, but quality looked a little worse near the complex “T” intersection of welds. Overall the welding appears to be similar to that found on A.E.B kegs (need to confirm with microscope).|
|Pressure rating:||The lid is stamped as 130PSI.|
Overall I am very happy with the quality of this keg. It feels sturdy and although the welds aren’t perfectly flat, they appear to be smooth and sanitary. Some are a little splotcy to look at, but even still they feel smooth to the touch. I would be happy to proceed with the 25 litre version of this keg.
23 litre keg
The manufacturer of this keg was very helpful to us even while we were organising our trip to China. The sample arrived quickly but unfortunately I have a few concerns about its suitability for home brewing.
|Construction:||Tall and skinny. End pieces are capped to overlap the main tube then welded on the outer edge only. Bottom is domed inwards like a drink can. Two carry handles that are sharp on the edges.|
|Surface Finish:||Appears to be electropolished, shiny silver finish. The edges are sharp and a little rough in places. The lid has black around the attachments and there is visible pitting in areas.|
|Weld quality:||All of the welds look quite good, but there are no welds on the inner joints of the end caps.|
|Pressure rating:||No pressure rating mentioned on the keg or the lid.|
My primary concern about this keg is that it is constructed with end caps that overlap the main cylindrical tube and that the inner seam isn’t welded. I worry that this may leave a tight groove that can harbour bacteria and yeast. Also, the inner edge is rather sharp and rough and this would also make sanitary cleaning difficult. Finally, the surface finish, lack of markings and general loose feel of the lid doesn’t fill me with confidence.
25 litre keg
This keg immediately showed itself to be a good candidate for Xymo. It looks and feels like it is built with high quality. The surface finish is consistent and there are no sharp edges.
|Construction:||Shorter and wider than the others. Metal parts are seam welded. The bottom end is domed inwards like a drink can. The carry handles are comfortable.|
|Surface Finish:||The keg has been electropolished leaving it with a shiny silver finish. The surface has a slightly rough texture to it that is consistent all over.|
|Weld quality:||The seam welds are almost perfectly flat. Special attention has been given to make the welds as tidy as possible.|
|Pressure rating:||The lid is stamped as 60PSI.|
Over all, this is my favourite keg of the three. It is hard to fault and I feel the welding is of a higher standard than even the A.E.B kegs we have at home.
With sample kegs in hand I was able to start designing our heatsink and thermal insulating jacket, but customisations still had to be made to the kegs to support our sensors and temperature controller. All three of the samples came from manufacturers in the East of China which meant that I would have to fly a long way to meet with them.
I organised a day trip to Ningbo to meet with the manufacturer of the 25 litre keg first, because I felt this keg was constructed with the highest attention to detail. The day started our with a generous spicy lunch followed by a tour of their metal working factory where they were just finishing a manufacturing run of thousands of commercial style kegs. I was lucky to see how their kegs are formed by drawing a flat sheet of stainless steel into a bell shape that forms the top or bottom halves of the keg. Structural curves are rolled into the sides of the keg, a hole is punched into the top bell and a fitting is welded in place. Finally the two halves are welded together on yet another automated welding machine and the base and lid handles are welded to the outside. All said, the process looks unnecessarily difficult and expensive, but the upshot is there is only one single seam holding the keg together instead of the three seams in a corny style keg.
A change of plans
Once I understood the construction process, I began asking my host about customisations such as replacing the beer in/out posts with small tri-clamp fittings. It turns out that my host had a lot of experience with tri-clamps and he showed me a commercial style keg that had a large 133mm ferrule instead of a small spear connection. This got me thinking…
- The 133mm (5″) tri clamp creates an opening that is easily large enough to fit an arm inside for cleaning. Much like the corny keg lid, but with a better seal.
- The 133mm blanking plates are available with threaded holes in them. Perfect for mounting airlocks, spunding valves and sensors.
- The commercial style kegs are technically superior to corny kegs because they have only one seam weld as opposed to three. They “should” cost much more, but they are actually cheaper due to economies of scale.
- The commercial style kegs are also available in 25 litre sizes with flat, vertical sides. Almost perfect for mounting our cooling block to the side!
This changes everything! So now we’re busy organising a sample of this new 25 litre commercial keg with 5″ tri-clamp. The heatsink will have to be altered with a gap that accounts for the middle seam in the commercial style of keg, but overall this is looking like a very promising development for Xymo that will result in a unique and effective fermentation vessel.