I’m back in New Zealand for a long overdue holiday and a visit to friends and relatives.
And since I’m here, I had to pay a visit to DB breweries’ Waitemata brewery to view the continuous fermentation system (cf). I wrote about cf earlier in this post.
The DB cf process was covered in brief in the earlier post. There are three main tanks. The tanks are all stirred to keep conditions homogeneous within each tank. The first tank, known as the hold-up tank, comprises 6% of the total system volume and blends vigorously oxygenated fresh wort (O2 25-45ppm) with actively fermenting beer from the second tank and recycled yeast to maintain a pH of <4.4 and ABV of >2.5%. Hold-up tank temperature is 9C. The cool, acidic, mildly alcoholic conditions help guard against bacterial infection.
The second tank is 63% of the system volume and is where the bulk of the fermentation happens. The tail end of the fermentation happens in tank three, which is 31% of system volume. The second and third tanks are maintained at 15C. A fourth, yeast sedimentation, tank finishes off the CF system proper. The yeast is washed with cold sterile carbonated deaerated liquor and some is recycled into the hold-up tank. CO2 is collected from fermentation and used elsewhere in the brewery and packaging lines.
I was really struck by how small the cf system was. The total system volume was 2000hl it is capable of producing up to 50hl of green beer per hour, meaning a residence time of 40hours, although my guide on the day, brewery technical manager Doug Banks, said that the residence time is varied between 50 and 90 hours depending on demand. The green beer undergoes a continuous maturation stage for a further 40 hours to remove diacetyl and then is ready for preparing for packaging (I assume this means clarification, and possibly bringing CO2 levels into product specifications). Traditional batch processes would need a huge tank farm to accommodate these volumes of beer (and in fact the Waitemata brewery does have a large tank farm because it also produces beer by the batch for different brands, notably Heineken). Before seeing it for real, I don’t think I’d really appreciated just what an enormous capital saving cf achieves. A quite physically small brewery could produce huge quantities of beer.
The other highlight of the tour for me was seeing the old brewhouse. It was built in art deco style and is a work of art as well as an impressive piece of engineering.
One interesting feature of the old brewhouse is a lactobacillus delbruecki reactor vessel for acidifying the mash. Lactic acid was produced in this vessel to bring the mashing conditions to optimum pH level.
It was a very impressive space. Beautifully uncluttered and beautifully designed and I can imagine it would have been a wonderful space to work. I don’t think the brewhouse is in regular use at the moment although it is still in working order.
I’m very grateful for the chance to view first hand a piece of New Zealand brewing history and happy to see one of New Zealand’s key innovations still going strong into the future. (Some people may be snooty and dismissive in a kind of reverse snobbery kind of way, but fermentation technology is in principle something every brewer can use provided they have the sales to justify producing beer in such large volumes. The details of the recipe matter for the earlier stages of wort production. Maybe in the future the likes of Brewdog or Sierra Nevada will use this technology for their flagship products).