What type of vessel did Scandinavian Vikings use to brew beer?

Short Answer: a large iron pot if they could afford one and a wooden bucket or a wood or stone trough if they couldn’t.

Long Answer:

Let’s go over the whole process by which people in the Viking Age would brew ale, as best as I can reconstruct it based on the sources that we have.

The very first step of brewing some ale would be a reason why you’d want to have a lot of ale. Ale was often brewed for specific events such as a holiday, feast, wedding, etc. Viking Age ale generally wasn’t the most shelf stable beverage so having a specific event where all of the ale would be drunk would be helpful to make sure that the ale is in good condition. This doesn’t mean that people wouldn’t have any ale sitting around, just that a lot of ale was purpose-brewed for special events.

So, if you want to brew some ale in the Viking Age what you would need to do is harvest your barley and then let them sprout just slightly. Then you would take the sprouted barley and roast it gently. We can find archeological evidence of Viking Age kilns/malt houses for this purpose, that were sometimes mistakes as sauna or bathhouses by later researchers. See this article by archeologist Merryn Dineley: exarc.net/issue-2013-2/ea/where-were-viking-brew-houses

This roasting was done with wood which would have given the beer a smokey taste. More modern Scandinavian farmhouse brewers often use alder wood for this purpose. For more information about modern northern and eastern European farmhouse brewing see the absolutely incomparable research of Lars Marius Garshol: www.garshol.priv.no This roasting dries out the grain so it doesn’t rot and helps to remove the sprouts that have sprouted out of the barley.

Then you would lightly grind the malted grain. You would not want to grind the malted grain into flour as that would make it very difficult to filter out later.

The next step is to cook the malted grain in water (mashing). This causes the enzymes in the malted grain to convert starches into maltose. Yeast can eat maltose and it has a hard time with starches so this is vital. This chemical process only happens between 62–67°C so you have to hit the right temperature range. The simplest way to doing this is to heat the water and malt up to this temperature and then hold it there for an hour or so. However, more complicated mash schedules are often used for various reasons that are beyond the scope of this post.

So, here’s where we finally get to your main question. What kind of mash tun was this done in? Well, if you could afford it, you’d use a very large iron pot that would be either heated up in an oven or over a fire. These vessels are mentioned in some legends such as the Hymiskviða (the story about Thor going fishing and catching the Midgard Serpent. To quote stanzas 2-4:

The mountain-dweller | sat merry as boyhood,

But soon like a blinded | man he seemed;

The son of Ygg | gazed in his eyes:

"For the gods a feast | shalt thou forthwith get."

The word-wielder toil | for the giant worked,

And so revenge | on the gods he sought;

He bade Sif's mate | the kettle bring:

"Therein for ye all | much ale shall I brew."

The far-famed ones | could find it not,

And the holy gods | could get it nowhere;

Till in truthful wise | did Tyr speak forth,

And helpful counsel | to Hlorrithi gave.

(translation from here: www.sacred-texts.com/neu/poe/poe09.htm)

We can also find archeological evidence of iron pots in Viking Age sites. See here for example: www.viking.ucla.edu/publications/articles/warmlander_zori_byock_scott_hrisbru_metals_2010.pdf

But a large iron pot, especially one large enough to create a very large batch of ale for a feast would be a luxury item. We can see in the Hymiskviða the whole motivation of Thor’s quest is to get a big enough iron pot. But what did you do if you don’t have enough money to buy a large iron pot?

Well, there are other ways of heating up water. One way of doing this is to heat up stones in a fire and then drop then in a wooden bucket or a stone or wood tough filled with malted grain and cool water. Here is an article about how that process worked by archeologist Geir Grønnesby: ntnuopen.ntnu.no/ntnu-xmlui/bitstream/handle/11250/2981018/Gr%25C3%25B8nnesby.pdf

Then you would pour out your mash tun into a large vat. People in Scandinavia would often use spruce boughs to filter out the spent grain, which would give the ale a bit of a spruce flavor. In order to make the grains go farther many brewers would then either sparge the spent grain (rinse it with water to get any leftover maltose out) or brew up a second runnings ale which involves mashing the used grain all over again (with a bit of fresh grain) to try squeeze every last bit of fermentable material out of the grain. I am not aware of any sources that indicate which of those (or neither, or another process) was used in Viking Age Scandinavia. Perhaps different methods were used in different times and places.

At this point modern brewers would then boil the wort (unfermented beer) for an hour or so with hops. In Viking Age Scandinavia hops were not used and boiling liquid for a full hour by throwing hot rocks in it would be incredibly difficult so Viking Age ale was almost certainly “raw ale” (i.e., ale that was never boiled). Raw ale can be delicious but it tends to have more protein in it (protein tends to settle out during the boil) which can make it thicker and spoil more quickly and will generally look a bit more turbid than modern ales.

Viking Age brewers might’ve thrown some berries or honey into the wort but they probably didn’t use much in the way of herbs. Herbal Medieval beers certainly existed (gruit etc.) but their prevalence tends to be exaggerated.

The last thing you need to add to the wort to turn it into ale is yeast. We have references to 16th century Scandinavian brewers reusing the yeast of previous batches of ale. In later centuries we know Norwegians used a kveikstokker (“yeast log”) to store yeast from previous batches. There are generally carved bits of wood that people would get fermenting yeast to stick to then let it dry and keep it in a safe place so that they could use that dried yeast in future batches. However, we have no way of knowing if the use of these went all of the way back to the Viking Age. Perhaps they just left the brewing vats open for a while so wild yeast could float in on the air. We just don’t know. For photos of kveikstokker see: www.garshol.priv.no/blog/264.html and https://medievalmeadandbeer.wordpress.com/2019/05/04/scandinavian-yeast-logs-yeast-rings/

Then the ale would be allowed to brew in large vats with a stone or wooden lid. Once it had fermented enough it was poured into barrels for transportation and storage. My speculation is that this fermentation period was often quite short as that wouldn’t give any bacteria that found its way into the beer much time to propagate and even if there was a bit of bacteria in the beer, if the yeast weren’t finished fermenting all of the available sugars, then there’d be some residual sweetness to balance out any bacterial souring.

As for the actual beer it’d probably have been reddish-brown, fairy turbid (proteins, yeast clumps, bits of grain that hadn’t been filtered out, etc.), have a smokey taste (apparently alder smoke is quite delicious), a bit of spruce flavor, be only lightly carbonated, and either be sweet or sweet/sour without any of the bitterness that modern beer gets from hops. Sounds good to me. The closest thing to this today would be Norwegian farmhouse ale which, again, nobody has done more research on than Lars Marius Garshol (www.garshol.priv.no).