RICHARD EHRLICH dons a professor's hat for an evening to teach the food writing students at London's City University a thing or two about wine. He chooses to do this with the sadistic' method of blind tasting, and although the results are not revealed, Ehrlich promises that sharpening one's tastebuds by blind tasting is as useful for budding food writers as it is for oenophiles'. This week's wine recommendations include 2004 Insignum Riesling (4.99; Sainsbury's).