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Porridge, for me, is made of oats, water, a bit of milk and a pinch of salt. Accompaniments are butter and brown sugar or, better yet, treacle, though I have nothing against people who add milk or even cream. So, while I’ve been aware of the inexorable rise of porridge in all its forms, I’ve been blissfully ignorant of the details. When I make, or eat, a risotto or a dal, I certainly don’t think of it as a porridge. Maybe now I will, and all because Laura Valli took the trouble to send me a copy of her research paper Porridge Renaissance and the Communities of Ingestion.
We had fun chatting about porridge, about how she helped start the only porridge cafe in her native Estonia, and about her participation in the World Porridge Making Championship last year, in Carrbridge, Scotland. As a result of which, despite the fact that I am usually the last person in the world to know about the international day of this, that or the other, I’m totally ready for Thursday 10 October and World Porridge Day.
Notes
- Thank you Laura for getting in touch and for your photos.
- On the spurtle, I welcome further details on why you should use one. In the meantime, I note that Neal Robertson, two time winner of the Golden Spurtle, despite having a quiver-full of spurtles to his name, uses a spoon in this video demonstration
- More on the 26th Annual Golden Spurtle® World Porridge Making Championship® and World Porridge Day
- NPR had a great article about Norway’s Traditional Porridge last year.
- Music adapted from bagpipe shredding by zagi2.
In honour of last week’s 29th annual Golden Spurtle championship, I refer you to two previous epsiodes.
Porridge: Not your usual all-day breakfast eatthispodcast.com/porridge/ and
Why a spurtle makes a superior porridge stirrer eatthispodcast.com/spurtle/
In honour of last week’s 29th annual Golden Spurtle championship, I refer you to two previous epsiodes.
Porridge: Not your usual all-day breakfast https://www.eatthispodcast.com/porridge/ and
Why a spurtle makes a superior porridge stirrer https://www.eatthispodcast.com/spurtle/
https://media.blubrry.com/eatthispodcast/p/mange-tout.s3.amazonaws.com/2020/spurtle.mp3Podcast: Play in new window | Download (Duration: 9:39 — 7.9MB)Subscribe: Android | Google Podcasts | RSS | More
Here, for the New Year, is a confession and apology.
I was completely wrong about porridge-stirring implements and I am here to make things right.
In the episode about Porridge, I mocked the idea that the traditional Scottish spurtle, which to all intents and purposes is just a stick, might be better for stirring than a spoon. My (faulty) reasoning was that a spoon offered a greater surface area to break up lumps. In fact, as I now know, the stirrer does not break up the lumps directly.
I noted in Eat This Newsletter 110 that a friend of a friend, who is a specialist in fluid dynamics, said that he had “a working, testable hypothesis”, which required only some worthy porridge in order to test it. So, I packed a bag of my favourite oats ready to meet up at Georgetown University in Washington DC.
I should explain that Dr David A. Gagnon, the physicist in question, is the son-in-law of one of my dearest friends, who happened to be visiting when I was editing the episode. That was how David came to know of my puzzlement – and he has access to wonderful machines that can make very accurate rheological measurements. Rheology is the study of flow, and David’s idea was that the faster the stirrer moved through the porridge, the lower the viscosity of the porridge would be. Shear stress in a material like porridge would be greater at higher flow speeds, and it is the shear stress that gets rid of lumps.
You can think of shear stress as being a difference in the speed of flow of the liquid across a small distance, multiplied by its resistance to flow. That resistance to flow is what we think of as viscosity. In a viscous liquid, like honey, the stirrer produces a lot more shear stress than it would moving through water at the same speed. But there’s a crucial difference between honey and water.
In water, the viscosity is the same no matter how fast the stirrer moves. Honey is different; the viscosity decreases the faster the stirrer moves. And that means that the stirrer produces more shear stress when it is moving quickly through the honey than when it is moving more slowly. David’s idea was that fast stirring would result in lower viscosity, and lower viscosity would result in greater shear stress.
To get back to porridge, and to lumps, consider a lump as the stirrer moves past it. Relatively speaking, the part of the lump in the slower flow near the edge of the stirrer is being held fast, while the part in the faster flow is being pulled away, and that’s what destroys the lump, pulling it apart.
The rheometer measures all that. It has two circular plates, one above the other, and the bottom plate can be rotated very accurately through a known distance at a known speed. David carefully loaded a little bit of porridge onto the bottom plate and then lowered the top plate to make contact with the porridge. The layer of porridge mechanically connects the bottom plate to the top plate, which in turn is connected to sensors that accurately measure how fast and how far it rotates. Meanwhile, David had programmed the machine to oscillate the bottom plate over a wide range of frequencies. The faster the oscillation, the greater the stress on the porridge. The machine then takes all those measurements and creates a set of graphs that describe the rheological properties of the porridge.
The viscosity graph, photographed directly from the screen.
The graph appeared and I confess it was really exciting to watch the points appear. A straight line down from top left to bottom right over a huge range of stirring speeds. As David had suspected, the viscosity declines linearly with the speed of rotation.
Like good experimentalists, we turned to a nearby, very heavily used whiteboard to try and get a grip on what was happening.
David drew a circle, a cross section through the spurtle, and an elongated ellipse, a cross section through a spoon, and flow lines as they moved through the porridge. For any given speed of movement, the energy needed to move the spurtle would be lower than the energy needed to move the spoon. Likewise, for any given amount of energy, the spurtle would move faster than the spoon. Shear stress depends on speed of movement. So, with a spurtle, it takes less energy to get a certain amount of shear stress and thus a certain amount of lump-disruption.
But there’s more. Because the viscosity of porridge goes down as you stir faster, the rapidly-moving spurtle is even better at breaking up lumps than the slower-moving spoon.
And that is why a spurtle is better for stirring porridge. It’s more efficient.
David’s diagram on the whiteboard, with my crude attempt to turn a spoon into a spurtle
Conceptually, my real breakthrough moment came as David was drawing the flow lines. There is a dead area, just in front of the spurtle and the spoon, where the porridge is not flowing past the stirrer. The dead area impedes the forward movement of the stirrer, and is considerably bigger for the spoon. However, if you remove the large blade of the spoon, you’re left with a spurtle.
And a cleaned up version of the whiteboard diagram
Some additional thoughts:
My friend Robert, David’s father-in-law, brought with him an Ethiopian stirring stick, with four mini-spurtles emerging from the main cylinder. You can see it in the photograph. Very, very effective, as they must have discovered long before rheometers.
A spoon with a hole in it, or even one with slots in it, would also be very effective at destroying lumps.
Maybe the reason a balloon whisk is extremely good at dispersing lumps in, say, a white sauce, is that it consists of a large number of spurtles, each one creating shear stresses in its wake.
And finally, David pointed out the most efficient method of all might be to stir porridge with a spoon or paddle keeping the blade parallel to the wall of the saucepan, because the long surface would result in a larger area of shear stress. Most efficient, perhaps, but way too difficult.
My overall conclusion: if you have a spurtle, use it. If you don’t, don’t worry about it too much.
Huge thanks to David Gagnon and Robert Seyfarth for making this bit of experimental fun possible. And of course, any errors in this account are mine and mine alone.
Notes
Shear-thinning is the technical term for no-Newtonian fluids like porridge, honey and modern, non-drip paints. Shear-thickening is much less common, and much more entertaining. (Blue Peter never used to be this much fun.)
Listened to Porridge: Not your usual all-day breakfast by Jeremy Cherfas from Eat This Podcast
A podcast episode that answers many burning questions I’ve long had about spurtles. I remember a few years back reading the back of a package of Bob’s Red Mill Steel Cut oats and their extended story of winning the Golden Spurtle which was almost written as ad copy in the style of the J. Peterman Company. Upon looking, I notice that Bob’s website has a Golden Spurtle specific tag, and honestly what self-respecting website wouldn’t? In any case, god bless Jeremy for digging into the science behind the spurtle, though it’s painful remiss that he didn’t link to any of his sources there. My only additions on the speculations about spurtles are:
From a historical perspective, having been made in the 1500’s when cooking fuel was at a higher premium and people may have been more likely to cook in larger/deeper pots over fire, a long thinner spurtle would have been somewhat easier to spin around in a deeper pot, particularly with more viscous porridges compared with soups which may be easier stirred by spoon.
From a manufacturing perspective in the 1500’s, it’s far easier to turn a piece of wood into a decorative cylindrical spurtle, than it is to make a spoon.
Without a flat spoon-like eating surface, using a spurtle makes it more difficult for passing family members to sample the porridge as it’s cooking.
I’m not sure Jeremy got to the root of his question about why porridge was hip and trendy, but I suspect that some of it goes down to the whole grain movement and the rising popularity of “exotic” grains like quinoa, which I recall he’s commented on before. Of course, many restaurants I visit will have at least a simple oatmeal on their breakfast menu, often for $10 or more and there’s nothing that will make food seem more mod than a 1000+% mark up on its fair market value. That combined with the comfort food aspect seems to get people every time, particularly when it’s difficult to mess up a porridge.
I will admit I’ve been eating a lot more porridge over the past few years, but part of it is the fact that I acquired a rice cooker which has a workable porridge setting that allows my grains to soak overnight and then automatically cook so that breakfast is waiting when I rise. My favorite is generally brown sugar with ripe strawberries and a splash of cream.
I was disappointed not to find Laura Valli’s paper Porridge Renaissance and the Communities of Ingestion linked to in the show notes, but apparently it’s because it either isn’t yet published or available online.
Jeremy buries the lede here that Neal is also sporting a serious arm tattoo that reads “World Porridge Champion 10.10.10”! Though I do wonder where he keeps the golden spurtle?
I will also admit that as I was making breakfast this morning, my choice of podcast was a bit biased.
Today’s breakfast.
Syndicated copies to:
I enjoyed the episode. And now I feel obliged to eat some oatmeal tomorrow which is as close as I can come. :-)