The main problem, obviously, is that you can't lauter and sparge in the same way that you would if you had used a wooden tub as a mash tun with a spigot, or if you had a bespoke lautering and sparging vessel. When the trough is in the ground, it's a different story.
There are thousands of sites throughout the British Isles that archaeologists know as Burnt Mounds. All that remains is a large pile of fire cracked stones and the remains of a trough lined with either stone or wood. If you have never heard of burnt mounds before, I suggest you have a look at an earlier blog which explains what they are and some of the interpretations. Archaeologists agree that they were used to make water hot. This was achieved by heating rocks in a fire then putting them into the trough of water. What you do with that hot water is up to you. There are many possibilities. Some interpretations include bathing, others suggest cooking meat and some archaeologists think that they were used as a sauna. Another function is as a mash tun. With the discovery of chaff and grain in an oak trough excavated in Wales in 2008, a mash tun is a strong possibility.
Trough mashing at Bressay, Shetland
|Replica trough at Bressay, Shetland, surrounded by fire cracked stones||.|
The original trough and buildings were moved stone by stone, since it was in danger from coastal erosion.
A replica trough and hearth was built beside the Bressay Heritage Centre, for experimental archaeological work. It's been used to dye wool, it has been used as a bath and also as a mash tun by archaeologist Dr Lauren Doughton in her experimental work.
We were there in the summer of 2011 to mash some malt with her when she was working on her PhD about burnt mounds and troughs.
The weather was rough, even though it was mid July. Buffeted by the wind and rain, we managed to run a mash and collect some of the wort. Our time was strictly limited because we had to catch the last ferry off the island and get back to our tent. A full set of pictures of the day's mashing, collection of wort and the final brew can be seen here on my Facebook page.
Brewers usually want to obtain as much wort as they can from the mash. There is potential for lots of waste from a trough mash unless you can find a way of maximising the wort extraction. The most obvious technique might be to let the grain settle to the bottom of the trough, then scoop the wort out using a jug or a bucket or something like that. It's tricky, as we discovered. Nevertheless, it works. Inevitably there will be bits of husk in the wort. This is not a problem. They will sink to the bottom again and it is easily possible to obtain a clear wort for fermentation from a trough mash.
|Locally sourced clay was used to seal the corners of the replica trough before we began the mash.|
Water was put into the trough. It became slightly murky, a grey colour from the clay luting that we had used to seal the trough. We were a bit worried, however, we did not need to be concerned because the resulting ale from this experiment was delicious, sparklingly clear and bright, perhaps the result of our accidental addition of clay to the water.
|The hot rock rolling team, from the fire into the water.|
The technique of rolling hot stones from the fire into the trough of water had been perfected by Lauren and her team in previous runs. Using garden forks and spades, the hot rocks were expertly rolled down the slope and into the water.
When the water reached strike temperature, 50 kilos of crushed pale malt was added to the 200 litres of water and stirred with a garden fork. You know when the water is the correct temperature for the strike, around 74 degrees Centigrade or thereabouts, because this is when you can clearly see your reflection in the water, no ripples, no steam. We double checked with a thermometer.
|The strike:adding the crushed malt to hot water.|
The saccharification takes about an hour and it's crucial to keep the mash temperature right for that time, adding hot rocks and stirring as necessary. We put a wooden board over the trough, to help keep the steam and the heat in. It was a good conversion of starches into sugars, a successful mash. The finished mash, when settled, was a deep dark brown and it tasted very sweet.
|The finished and settled mash - the next job is to collect the wort and ferment it.|
We were short of time and collected as much wort as was possible. The brewer used jugs, buckets and plastic containers to scoop from the trough. We had, of course, taken the stones out first, when they were cool enough to handle. The process of collecting the wort was hard work and we only managed to get about 6 gallons out of the trough before we had to pack up, load the van and catch the last ferry back to the Shetland mainland.
|The brewer collects wort from the trough. The stones have been removed and are on the heap.|
The wort was put into a fermentation vessel, yeast was added and the fermentation vessel was kept warm using sleeping bags as insulation. After about four or five days it had fermented into a fine, clear and strong ale. We used a handful of dried meadowsweet flowers as a preservative.
This is how we should have collected the wort
On the ferry back to mainland Shetland we realised that we had made a mistake. We should have piled the stones up in the trough to make a sort of dam, then we could have put the mash to one side and the wort would have been so much easier to collect. This is how the Moore Group archaeologists collected the wort at their trough mash demonstration at the Sixth World Archaeology Conference in Dublin, 2008.
They made a wooden trough and painted the bottom part with bitumen to ensure that it did not leak. They correctly assumed that the University authorities would not allow them to dig a big hole and set their trough in the ground.
|Moore Group archaeologists filling the trough with water at WAC 6, Dublin|
Here are some of my photos of the Moore Group's event:
|1 heating the rocks|
|2 heating the water|
|3 saccharification: the mash|
|4 the stone dam, mash and wort separated|
|5 settled wort and mash|
|6 collecting the wort, it's cloudy because it has been stirred up.|
Hot rock mashing is a spectacular process, the stones sizzle as they hit the water, the mash saccharification happens right before your eyes and the aroma from the mash smells delicious. This is a mysterious, magical transformation from grain starchiness into fermentable sweetness. Surely this would have been an event that would have amazed and impressed people in prehistory, just as much as it does in modern times.
Collecting the wort like this, by creating a dam of stones, is an extremely efficient way of doing it, perhaps even allowing for sparging. Once the first runnings have been collected from the trough, more hot water can be poured gently through the mash, thus releasing more wort for the brewer. There would be very little waste and a good quantity of wort could be collected.
Is there any archaeological evidence for the collection of wort like this?
It is rare that prehistoric troughs are excavated with the stones still within them. If you have excavated one like this, I would love to hear about it. Excavations in 2013 by Wessex Archaeology at Kingsmead Quarry, Horton, in Berkshire, England revealed the remains of four neolithic buildings. They were interpreted as having been 'houses', which is often the case with these discoveries. I do wonder how many of these neolithic 'houses' might have been used as barns or as buildings where the grain was stored and processed. But that's a story for another blog.
One of these four neolithic rectangular timber buildings at Horton caught our attention when we were looking at the pictures online. There appear to be some fire reddened rocks close by one of the buildings, in a heap. Here are the pictures that intrigued us, taken from Wessex Archaeology's web page, and the rocks can be seen in the picture on the left, in a pile at the bottom left hand corner of the building.
|Two neolithic buildings at Kingsmead Quarry, Horton, Wessex, full story and pictures here|
They do look rather like modern bricks, but the stratigraphy indicates that they are contemporary with the building. So, are these stones an indication of hot rock water heating technology at neolithic Horton? Were they piled up in a wooden trough that has long rotted away? What were the people doing in and around this rectangular wooden building, over 5000 years ago?
I cannot answer these questions. I am nevertheless intrigued by this discovery. And so I finish this blog with a close up (thanks to Graham) of those mysterious fire reddened stones and welcome interpretations, comments and discussion.
|a close up of those mysterious fire reddened stones beside the neolithic building at Horton|
If you want to know what our Bronze Age Trough Ale, with meadowsweet, tasted like, we sent some to Mr David Connolly of BAJR (British Archaeological Jobs & Resources). Although he struggled to open the parcel, he gave his opinion on the ale's flavour and strength. It is sometimes said that prehistoric ale was weak, cloudy and sour and that it tasted disgusting. We disagree.
Here is the link: https://www.youtube.com/watch?
Quinn, B., & Moore, D. 2009 ‘Fulacht fiadh’ and the beer experiment’ in Stanley et al (eds) Dining & Dwelling. NRA Monograph Series No. 6, 43-53, NRA, Dublin.