The shop where Alain Ducasse and Joel Robuchon buy jam, and how to replicate its special ingredient

About a year ago, I went to the little village of Niedermorschwihr, in Alsace, France, to meet Christine Ferber at her shop, Au Relais des Trois Epis. The store is so pretty, and packed with so many delicious-looking things, it feels as though it came out of a Hansel and Gretel illustration. Ferber is a pastry chef but her speciality is jams, jellies and other preserves. She's so good that chefs such as Alain Ducasse, Pierre Herme and Joel Robuchon have asked her to make special flavours for them, which are available only at their restaurants and shops.

Ferber was generous with her time and knowledge about jam. She uses no more than 4kg of fruit in each batch; she mixes it with sugar and lets it sit in the fridge overnight (this helps to pull the liquid out of the fruit and starts to dissolve the sugar, so it needs less time to cook, thus maintaining a fresher flavour) and then simmers the ingredients in copper pots (the copper reacts chemically with the fruit so it sets faster).

Ferber eschews the use of commercial pectins in her jams; instead, she relies on pectin extracted from what she calls "green apples". She's not referring to green-skinned varieties, such as Granny Smith, but the unripe fruit. Apples are relatively high in pectin anyway - it's concentrated mostly in the skin and pits; and unripe fruits of all kinds have more pectin than fruit that is fully ripe. In her kitchen, Ferber had buckets full of small, green, unripe apples that would be mouth-puckeringly sour if eaten out of hand, but, when cooked with water then filtered, yield a clear juice that solidifies at room temperature and is capable of "setting" jams made of fruits with low pectin contents.

Because I haven't been able to find these green apples in Hong Kong, and because I dislike commercial pectin, I sometimes combine low-pectin fruit with the skins and seeds of regular (fully grown) apples. I buy unwaxed, organic apples, but if I can't find them I scrub the fruit well. After peeling the fruit, put the seeds and skin in a mesh herb bag (which is similar to a tea bag) and tie the ends - this makes it easier to remove and discard these ingredients after the jam is made. I have experimented with commercial apple pectin but it's hard to estimate how much to use, so after making batches of jam that were too firm, I've given up on that. My jam sets a little softer than the type with added pectin, but the flavour is pure and intense.

Truc (tryk): noun, masculine, trick, gimmick, device. A French word for a chef's secret.