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Apparently these grapes were developed in California from the Lambrusca variety. Thank you, California. The first supermarket to introduce them to the UK was Sainsbury's. Thank you, Sainsbury's. Keep up the great work.
But then these tasty little rascals vanished from the shelves and I began to fret that I'd seen the last of them. I kept searching, despondently, to no avail. Other high-end grape varieties, like Sable, had been exposed as the boring impostors they were. It was cotton candy grapes or nothing. Or, rather, it was cotton candy grapes or whatever grapes were available in Sainsbury's Basics range (often excellent, though constantly varying and unpredictable) for £1.25 per 500g.
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I bought three. Just as well because the Waitrose ones didn't survive long after I got home; my Sardinian neighbour, who'd also been mourning their absence, helped me demolish the punnet. In fact, he ate most of them, the scoundrel.
I'd highly recommend these if you haven't tried them. If you have, you're probably already addicted.
As I've indicated the current best deal is from Marks & Sparks. These ones are Brazilian, taste great, and are disappearing from my refrigerator even as I write these words...
(Picture credits: the Waitrose pack shot is from here. The rather more attractive Sainsbury's one from here, where you can read more about the variety. Thanks, chaps.)