A firm, fruity olive is a beautiful thing, so why is it so hard to find? Purity of flavour is what olive-lovers crave, but frequently what is on offer is a plethora of antiseptic-tasting, flabby specimens, stuffed with synthetic pastes, or drenched with incongruous marinades.

How do green and black olives differ? Green olives are picked when unripe and hard. At this point they are bitter and inedible and have to go through a brining and fermentation process. Traditional methods involve soaking in water then brine, until the olive is completely fermented and cured (and “bad” bacteria is destroyed), and has a fresh, fruity flavour and a slight crunch. Faster, more commercial operations, however, involve soaking in caustic soda to remove the bitterness, before brining and heat treating. “Black” olives are green olives that have been left on the tree to ripen, become softer and more oily. As they do so, they turn darker, but are rarely uniformly black. When you see boot-polish black olives, in fact, they are green olives that have been soaked in water with oxygen running through it to turn them black. Then they are fixed with ferrous gluconate (E579, which must be listed on labels).

Are most olives in jars and tins heat-treated? Those in jars will usually have been heated to pasteurise them, while those in tins will usually be sterilised, “which involves heating to 125C for 35 minutes”, says Giles Henschel whose company Olives et Al is a champion of the best quality olives, free of heat-treatment. “It impairs the flavour; some people complain of soapiness, or a metallic flavour, or a chemical aftertaste.” Henschel and his wife Annie source their slowly cured olives meticulously, then soak them in water again to remove excess saltiness, before stuffing or marinading, using recipes gathered from the country of origin.

Is it better to buy olives whole, pitted or stuffed? Purists prefer whole olives – because, as with many a fruit, as soon as you damage the skin (to take out the pit), it starts to deteriorate. As to stuffings, olives that have been pitted by hand and stuffed with natural ingredients are best. Olives stuffed on an industrial scale are often filled with synthetic pastes. In the case of pimientos, these are ground up and mixed with gelling agents to make a paste. This is fed into a machine which whizzes the olives through, removing the pit and replacing it with the paste. Amazing, yes, but appetising? No.

Where to buy: Olives et Al (01258 474300; www.olivesetal.co.uk). The Fresh Olive Company (020-8838 1912; www.fresholive.com). Traditionally cured olives also sold through the Belazu label (020-8838 9670; www.belazu.com). Simon Whitfield’s Osmin Olives dresses slowly cured olives with local herbs, stuffs them by hand or marinades them (01547 540237; www.osminolives.co.uk).

Readers’ queries

Can you suggest a good source for rosé veal?

Helen Browning raises her veal calves in exemplary fashion at Eastbrook Farm, to produce flavoursome pink meat (01793 790460; www.helenbrowningorganics.co.uk).

If you have a food query, e-mail food.detective@thetimes.co.uk

Explore Food & Drink

• Gordon Ramsay

• Heston Blumenthal

• Recipes

• Wine

• Real Food

• Drinks

• Anjum Anand

• Eating Out

• Video Recipes

Times Recommends

• Britain's Top 20 seaside fish and chip shops
• Ice cream makers: the scoop of the century
• British berries make super sorbets