An essential ingredient in brewing is the yeast. A delicate living fungus, it needs to be cultured, nurtured and kept happy in order to ferment the wort to make beer and develop those interesting flavours in the process. At the end of a fermentation there will be considerably more yeast than when you started. Some of it will be dead or exhausted but some will be healthy and ready to fight again another day. Brewers who brew regularly know that they can crop their yeast - either top cropping or bottom cropping - while the fermentation is vigorous and there will be billions of cells in every millilitre with which to start off the next brew. Just keep it safe from infection, pop it in the fridge until required in a few days time or pitch it straight in to the next brew if there is more than one fermenter and the brewery is going flat out.
If you brew only occasionally - say every few months or even just once a year - how do you keep your yeast until it is needed? It won't keep indefinitely in the fridge. Most of us will just order some fresh or dried yeast from the supplier every time but there are some yeasts that are unobtainable that way, while in the past that simply wasn't an option.
In Norway, they have utilised the natural property of yeast cells that when they dry out they go into suspended animation until woken up again by re-hydration. It happens all the time in nature and it is a godsend for the occasional brewer. Traditional Norwegian brewers have found several ways of achieving the goal of drying a reasonable quantity of yeast, keeping it safe and then re-hydrating it for later use. What they are looking for is some kind of substrate that can be sterilised, has a reasonably surface area, is absorbent, stable, non-toxic and with lots of nooks and crannies where the yeast can nestle.
One solution was to take freshly laundered and ironed linen. This is pretty sterile immediately after ironing and when the yeast slurry is folded away inside the cloth it wicks away excess liquid and allows the yeast to dry out. When dried, the yeast could be picked off in small pieces or sheets and stored in a box or drum until required. Perhaps the most natural solution is to take a small section of a tree branch, the more gnarled the better, possibly with bark on it; boil it to sterilise and then dip that into the yeast slurry and hang it up with a piece of sterilised string in an airy place to dry. It can stay like that indefinitely.
A further development is to take a block of wood, drill lots of holes all over it to provide the nooks and crannies, boil it to sterilise and then, when cool, dip that into the yeast slurry and hang it up to dry. This is called a yeast log in English or in Norwegian it is a 'kveikstokk': kveik being the rather special yeast employed by traditional farmhouse- and home-brewers, who have kept it going for generations, nay centuries.
|One of my yeast logs (kveikstokker) well plastered with fresh yeast slurry|
from the bottom of the empty fermenter and hanging up to dry.
150 mm x 45 mm x 38 mm
|Sigmund Gjernes holding his yeast ring (photo: Lars Marius Garshol)|
* I have since learned that the photo above was the first and only time Sigmund has actually used the ring with yeast. Apparently, no one uses them at all nowadays. Aah, what a shame.
|Yeast ring made by Martta Pöllänen and discovered on the blog of Hans Haverman|
I went to Voss in September 2015 on a mission to taste some traditionally brewed 'maltøl', or more specifically 'vossaøl' as made around Voss in Western Norway (see previous bogs My Trip to Norway parts 1-4). While I did meet Sigmund and he very kindly and generously gave me a couple of litres of vossaøl I never got to visit him at home, nor see his yeast ring 'in the flesh' before my schedule took me back to Oslo. I also visited the Voss Folkemuseum where there is a perfectly preserved set of ancient wooden farm buildings (Mølstertunet) including a brew house but they didn't have a yeast ring on show and though I have inquired since, if they have any yeast rings in the collection, I am still waiting to hear back from them.
In November 2015 I began to think about making a yeast ring like the design by Martta Pöllänen and drew some pegs to scale, guessing at the design and dimensions by taking clues from the photographs. Fingers and eyes of people in photographs tend to be fairly fixed in size, so by using them as a scale I got some idea of the size of the pegs. Sigmund's yeast ring looked as if it had 90 pegs and the design from Martta Pöllänen had 63 (both multiples of 3 I noted). I began to make a few pegs from any old wood I had around, which was cheap pine timber. The photographs suggested to me that the Norwegians used pine.
I had my portable work bench set up in the brewery and was working away with circular saw and hand tools. I was interrupted by a charming couple from Nottingham who were interested in buying some beer. Naturally we got chatting about what I was up to. The gentlemen, whose name was Gerry Gamble, could see that I was making hard work of it by cutting out every peg, one at a time, by hand, cutting slots and whittling with a craft knife. Indeed, it wasn't efficient but I was feeling my way to create a prototype and to find out how it all fitted together. I wasn't worried about speed or efficiency at that stage. I had created half a dozen pegs by then and I could see that by slotting one peg through the back of the previous, they would all join up eventually. What I could not get my head around was how they would join up at the last peg to complete the ring. There would have to be a modified last peg I reasoned but I would solve that problem when I came to it.
This chance meeting with Gerry was one of those strokes of luck that I keep alluding to in my blogs, for it turned out that not only was he retired but was also in possession of a well-equipped workshop and he was keen to use it. Furthermore, he had acquired a baulk of the finest Baltic pine timber that had been taken out of the belfry of an old church. And here he was, exactly at the right moment! He offered to machine me up a quantity of blanks that I could finish off by hand and moreover he suggested that if he made me a jig or template to help me I could drill out the slots accurately and quickly, two at a time. True to his word, about ten days later a parcel arrived containing 70 beautifully made blanks of fine- and straight-grained Baltic pine and a steel jig for drilling. When I lined them all up they looked like the keys of a piano.
|Machine-cut blanks in which I have drilled and cut slots.|
Number of pegs : 70 (identical, except for the last one, which has a slimmed down 'beak')
Length of pegs : 83 mm
Width of pegs : 16 mm
Height of 'beak' : 10 mm
Length of 'beak' : 30 mm
Thickness of tail : 5 mm
Slot : 7mm x 20 mm
Diameter of ring : 245 mm
Weight of ring : 256 g
|A finished peg with the beak shaped by hand with a craft knife and the corners chamfered.|
|To assemble the ring keep pushing the tails through the back of the |
previous peg and with the beak in the same orientation as the one below.
|The finished ring. Note the spiral twist.|