Like many of us, Calloway Crossing cabernet shiraz was confused about its place in the world.

It could never decide whether it was a sophisticated blend for connoisseurs or bargain booze for the masses, and spent years flipping between £9.99 and £4.99. So what was it really worth?

The answer was "£3.99" according to wotwine? a new app whose team of experts blind taste thousands of bottles and estimate a fair price. While that's clearly subjective, I suspect many of the worst-value wines do lurk among those spurious half-price deals. Calloway Crossing may have been retired from service, but countless examples remain in the supermarkets.

The German discounters, Aldi and Lidl, take a different approach. "We try and be much more transparent on our pricing," says Lidl's drinks buyer, Ben Hulme. "Rather than do two weeks a year at a good price, and fifty weeks at a high price, we'll offer a good price all year round." Last November wotwine? rated Lidl best value on the High Street with two thirds of its wines priced below their estimates.

It is true the chain's basic range is hardly over-priced, but it's not exactly mind-blowing either. You simply don't find wines that thrill from the sort of producers who can supply the volumes and prices required, but Lidl's quarterly Wine Cellar promotions are different by offering smaller, one-off parcels until they sell out.

Last September Lidl swelled its meagre French selection with 48 wines, half from Bordeaux and rising in price to an eye-popping £25.99. "Pretty risky?" I suggest. "Well, it could have worked out not great for me," says Hulme. "But in short, it was a success, and in the year to February our sales grew 38% in value." It seems his only regret was not ordering more sweet pudding wine, which sold out within weeks.

Hulme explained Lidl's thinking: "If you want to trade up from our Bordeaux rouge at £3.99 to a St Emilion Grand Cru you can, and here's why you might want to." It used TV, leaflets and scores from master of wine Richard Bampfield to persuade people to spend more. All staff were given tasting notes in case anyone asked how the Margaux was drinking, as if they would. Portugal will feature in the store's next Wine Cellar promotion later this month, and there are plans for a new range of Scottish beers.