As the rouble loses value against the US dollar and inflation increases, what do buckwheat sales say about the Russian state of mind?
Legend has it that, 1,000 years ago, when Greek monks spread Christianity to Russia, they brought with them more than just the Bible. They brought a grain, a seed, so magical, nutritious and delicious that it struck an instant chord with the Slavic soul - and the Russian stomach.
That grain was buckwheat.
And because the first people to cultivate it here were Greeks, the Russians called it grechka.
Ever since, Russians have been boiling it and baking it, making porridge and pancakes with it, loaves of bread too - and cutlets.
On dinner plates across 11 time zones in this, the biggest country in the world, you'll find buckwheat in kindergartens and field kitchens, plush restaurants and factory canteens.
Forget vodka and beetroot soup. It's buckwheat that's really part of the Russian identity.
Those fluffy brown grains deserve a place of honour on the Russian flag. The nation's symbol, the double-headed eagle should, I think, be depicted tucking into two bowls of porridge.
And what about adding a line to the national anthem? "Oh glorious grainy Russia, land of my buckwheat."
I love grechka. (You've probably gathered that by now.) So imagine my distress this week when I walked into my local supermarket and couldn't find any. There are normally five shelves there full of the stuff - but panic buying had left them empty.
Why the panic? Well, in recent weeks buckwheat prices across Russia have shot up. In some areas by more than 50%. Rumours are swirling about bad harvests and grechka shortages.
The Russian authorities say there's nothing to worry about. They've accused "speculators" of trying to make a quick buck - from buckwheat - by creating an artificial crisis.
Some of which may be true. But the interesting thing about buckwheat is that this is more than just a packet on a supermarket shelf. It's a barometer of the social-economic state of Russia.
It's like when people feel they're coming down with a cold, they stock up on tissues. Well, when Russians sense an economic crisis brewing, the first thing they'll do is stock up on buckwheat.
And, right now, the Russian economy is exhibiting more than just a sniffle. Inflation is increasing, so is capital flight, while this year the rouble has lost a third of its value against the dollar.
The falling price of oil is a huge problem for the country, because the Russian economy is so dependent on energy exports. Western sanctions are playing a part, too, in all of this - they make it much harder for Russian banks to raise money on international financial markets.
But how is this affecting ordinary Russians? Well, at the Moscow motor show last month one visitor told me that, for the first time in a long time, he couldn't afford a new car - credit had become too expensive. He was only there, he said, to window shop.
This week a teacher told me she'll be spending her winter break in Russia. Because of the plummeting rouble, she can't afford to do what she normally does at new year - and that's take a holiday in Europe.
And that brings me to what is known here as the Eternal Russian Question - "Who is to blame?" Who does the Russian public hold responsible for disappearing buckwheat, for rising prices and an ailing national currency?
To find out, I grab my microphone and take to the streets of Moscow.
Pensioner Alla Giorgievna tells me that because money's tight she's stopped buying new clothes and cosmetics.
"All this is America's fault," she says. "The United States organised that revolution in Ukraine. And now the US is punishing Russia."
I talk to Vera. "The international community has it in for us," Vera tells me. "We'll have to duck and dive to get through this."
And then I speak to Alexander. He's a builder. He complains that his salary is being eaten away by rising prices. But he doesn't know who to blame. He says he doesn't really think about it.
"All I want," Alexander says, "is to have a regular job with regular pay. I just want stability."
Stability is what Vladimir Putin promised the Russian people 15 years ago, when he came to power after an era of economic chaos.
For now, Russians are not blaming their president for their current problems. President Putin's approval rating remains sky high.
But Russian history teaches us this, that just as supermarket shelves can be full of buckwheat one day, and empty the next, so, too, can a Russian leader lose the support of his people, quite suddenly and unexpectedly.
If the economy crashes.
If that stability disappears.
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