Background
Once you have harvested your first beautiful crop of grains, you might ask yourself,
“Now, how do I get from this to dinner?”
It’s a good question to ask at some point. Unlike pulses/dry legumes, we often grind grains before eating them. Some (rice, barley, oats, spelt, emmer, einkorn, foxtail & proso millets) also need dehulling before they can be eaten. Fortunately, millions of people around the world have dehulled and ground grains successfully through the centuries. You can too.
We tend to grind our grains in a Corona/Victoria mill, a little hand-cranked mill with metal burrs. This does not work for dehulling. To dehull grains (mostly foxtail millet), we made a large wooden mortar and pestle, similar to those used historically in central/west Africa and also in east to central North America. It would also work fine for grinding flour corn.
A mortar and pestle consists of two parts. The mortar is a stout bowl-shaped thing in which you put the grain to be pounded. The pestle is the pounder-thing (think pestilence). Pestles are easy to make: they are just a nicely-shaped and balanced stick. Mortars are harder to make, since you have to carve a deep hole into a log.
Two disclaimers. One: we are by no means experts at the process of mortar-making. We have done it only once, with moderate success. There are, no doubt, professional mortar-makers who are much more skilled at this than we are. Our only problem is we don’t know any of them, and couldn’t figure out how to get an introduction to any either. Please, though, make a good attempt to find one before blindly following our directions. We share what we did only because we did learn a bit which may be helpful to others.
Two: our technique involves fire, sharp tools, and a fair bit of effort. It ain’t our fault if you get hurt trying to do this. Please work carefully – but it’s not really that hard. Anyone who is moderately competent around fire and woodworking tools can do this.
When making our mortar, we worked from an article on Jon’s Bushcraft describing Jon’s attempt at mortar-making. We recommend reading it, and comparing our learnings. Jon insists that you should use well-dried wood for this method to prevent splitting. As people who aren’t good at planning projects ahead by a few years, we didn’t have a dry log of this size. Our past attempts at burning in green wood did have trouble with splitting.
For the attempt we show below, we used fresh-cut green wood and a combined strategy of rough-shaping the cavity using tools, then burning it a bit to finish the shape and remove some unevenness. This is likely somewhat faster than just burning, although it’s hard to say. It did split, but not enough to impede functionality. A disadvantage is that this does require a few more tools than just burning.
Preparation, Tools & Materials
To make a mortar, it is helpful to have a collection of hand tools. We used:
Probably fairly essential
– square
– drill with large, long bit (we used a brace and bit with a ¾” bit; if you don’t have this you may need an extension)
– 1” and ½” chisel and mallet
– pliers
– hook knife
– a fire with nice coals
– some kind of way to make/direct wind – see below
Nice to have, but not essential
– draw knife
– froe
– sliding t-bevel
– a woodstove to keep your fire in
For the mortar you will need a section of a large hardwood log about 20-24” long, ideally cut perfectly square on both ends. The log should be 10-12” in diameter. We used freshly cut white ash; it ended up cracking, though it is still quite usable, to prevent this, you might have better success using a well-seasoned log; however, it will be harder to work.
For the pestle, you need a stick about 4 feet long; thickness depends on your strength. Our finished pestle is 3” in diameter.
Instructions
This project involves using both sharp tools and fire. You are responsible for your own safety. Once you understand the process, think through how you can do it safely with your tools in your context.
Cut a section of log roughly the length of the finished mortar height and a bit bigger in diameter. Make the ends as square to the length of the log as you can; it will make everything easier later. We were guessing in terms of size; our log section was roughly 20” long and 12” in diameter. Green wood is easier to cut but, as noted above, may have more issues with splitting.
If the log is very far out of round or is just too big, you may wish to start by splitting some wood off the outside to make it as light as possible. You’ll be moving this thing a lot before you’re done shaping it, and it’s nice to not have to haul around extra weight. A froe and mallet is an easy way to bring it roughly down to size.
If using green wood, start working on the cavity promptly before the wood has a chance to develop big checks (cracks in the end grain).
Lay out the circle of the cavity diameter on the top end. We used an 8” diameter.
Making a mortar involves two basic stages. The goal of the first is to remove wood as quickly and easily as possible to form the approximate shape of the concave. The goal of the second is to smooth the inside enough to make a nice, even, easily-cleanable inside surface.
To start roughing out the cavity, drill angled holes from just inside the circumference of the circle to a central point just above the finished depth you’re aiming for. The goal is to define a deep cone of wood that will be relatively easy to remove. A bevel gauge is useful for aiming the drill at the correct angle. To find the angle to drill at, draw a rectangle half the width of your mortar and 1 ½ inches shorter than the depth. Place your bevel gauge on it and set it to match the diagonal. Mark a point on the bit at the depth you’re aiming for so you never drill a hole too deep.
Do a bit of figuring to see how many holes you need to get around the circumference. Using a 13/16” bit, we found 24 holes would nicely fill the circle leaving only thin bits of wood between holes, so we divided the circle into sixths so that we could space the rest evenly by eye. A brace and bit is a superb tool for drilling large-diameter holes. Still, there’s a lot of boring to be done here. Make sure the bit is sharp, take breaks (or trade off with your brother), and use the longest-sweep brace you can find. Place the bevel gauge on top of your log and line your bit up with it to guide your angle as you start each hole. Start with the six evenly spaced holes, then go half way between them and drill six more, then halfway again to drill the last twelve. Since the holes are all converging to a point, the later ones will run out into their neighbours and you won’t be able to go to the full depth.
After boring, the cone of wood is still firmly attached by all those thin bridges of wood. We removed it by splitting pieces from the cone outward using a chisel. Of course, working from the top, it is not quite possible to cut the bottoms of the debris-pieces loose. So we grabbed them with the pliers and wiggled and pried until they broke loose. We did this in three “layers,” alternating drilling and cleaning out, working about 3” deep each time, to make a hollow about 9-10” deep.
If you find a thick bridge of wood, you can bore down it to reduce what needs to be chiseled. Once you get to the bottom, make it as flat as you can by boring holes to the same depth and chiseling or boring as many of the walls between them as you can. Try to widen the cone outward toward a cylinder by splitting down around the outside of the circle, but be careful that you don’t run a split too far. Leave some extra wall thickness in the lower part – it’s hard to remove anyway and will protect the walls down there from getting too thin when you’re burning.
Burning is a great way to smooth out the rough hollow and increase the diameter at the bottom where it’s hard to reach with tools. DO THE BURNING OUTDOORS FAR AWAY (AND DOWNWIND) FROM BUILDINGS OR OTHER FLAMMABLE THINGS.
However, you can’t just have a fire in your log – there’s not enough air and loose fuel down in the hollow to keep it going. So you’ll need a good fire somewhere else, from which you can keep taking coals to drop into your log. We heat with a wood stove and did this on a winter day, but you could also use a campfire.
Drop a cup or two of live coals into the bottom of the cavity. The coals will work away if you leave them just sitting there, but progress will be quite slow and less directional than if you provide some supplemental air. We found that they actually seemed to smother themselves. We tried just fanning them with a sheet of cardboard, but that didn’t work very well.
I remembered reading somewhere that Bronze Age copper smelters heated up their fires by blowing on them through a tube. So we also made a wooden “straw” to blow through by boring lengthwise down a stick, then shaving down the walls with a drawknife until they were thin. Using a straw to blow through, you can direct the intensity of the fire quite well and speed up the burning significantly. However, we learned there is a crucial rhythm to this task. Blow on the fire, then take the straw out of the log, turn away, inhale (not through the tube), turn back and blow again.
The end of our straw started catching fire (of course), so we had to keep dunking it in the snow to put it out.
Inhaling while it was down in the fire could have pulled the fire back up the tube; inhaling even through the extinguished tube was an unpleasantly smoky experience. Note that no Bronze Age smelters are alive today. I suspect it is due to momentary inattention while doing this task. We eventually tired of huffing and puffing and smoking ourselves. It happened to be a windy day, so we just made a wind scoop from an old sack attached to a stick. When the wind’s going, this makes the burn a lot faster. However, it’s not very controllable and not continuous. If you have materials and time, you could make some sort of bellows to pump in air and get the benefits of both directionality and a higher blowing rate than your lungs can provide, but we didn’t. Ah, fire! Didn’t that add a lot of excitement to this project?
We didn’t want much thinning high up on the walls of the cavity, so we kept the fire down in the bottom as much as possible. Wetting the parts you don’t want burnt further helps for a bit, and applying some wet clay can help for a bit longer.*
The burning didn’t progress evenly for us; deep fissures opened up into the charred wood. So at intervals we would dump out the coals, make sure the fire in the mortar was out, and scrape the weakened, charred wood back to sound wood so it would burn as evenly as possible. A hook knife worked well for this, but a sharp stone would probably also work if you you like being neolithic. Then we would dump some fresh coals in and repeat. This process also gives a chance to see the progress of the hollowing more clearly without coals and smoke in the way so you know where to focus the fire.
Once the burning is done, all that remains is some final shaping. The best tool for the inside is a hook knife. We wanted to widen the bottom part of the cavity a bit more and remove as much of the surface cracking in the burned wood as possible, so it took some time.
Then make the bottom of the mortar square with the hollow. To avoid any wobbling during use, you may want to use a chisel to make the bottom slightly concave.
That done, you can clean up the outside as much as you like. A drawknife is a terrific tool for the job. Keep your fingers tucked well in (or wear gloves) – I drove a sliver through the side of my pinky and up under the finger nail doing this.
If the bottom surface of the mortar is cut nicely square to the direction of the grain, it’s not to hard to shape it into an even cylindrical shape. Mark a line concentrically around the opening at the desired wall thickness (a generous inch is good), then shave from the bottom toward the top until you’re down to the line all around. Now set the mortar upright on a flat surface and use a square to mark high points with estimated thicknesses to be removed. If it’s just a nice even taper out to the base of the mortar, you can mark the distance in from the edge on the bottom and shave top-to-bottom down to the mark.
Finish the top rim by chamfering the inside and outside corners (rounding them off with a chisel). This removes the risk of hurting yourself on those corners during use, and prevents splitting or mushrooming if you happen to hit them.
Shape the pestle from a stick or rived (split) piece of a log about 3 ½” in diameter. A draw knife used in conjunction with a shaving horse is the easiest way to do this. Leave the bottom end large (and the top end for balance, if you like) and shave the middle down to a pleasant size in the hand. Use a chisel to round the working end of the pestle so that it can make solid contact in the curved bottom of the mortar’s cavity and so that the corners don’t split off with use. Smooth the part you’ll handle with a spokeshave, sandpaper, or a piece of broken glass.
If you did use green wood, dry the finished mortar gently to prevent needless cracking, but don’t worry too much about some checking – it’ll just fill up with plant material over time and shouldn’t be a problem.
Now you have a mortar and pestle. Go make some hulled grain edible!
*Confession: this was our second attempt at making a mortar. Maybe that’s why we sound so experienced? On the first we followed the description on Jon’s Bushcraft, burning from the start. Our hole became too wide compared to depth, and our attempts to protect the sides with wet clay failed.
