How to make jam
As a nation we’re very passionate jam makers and terribly polite eaters - not the best combination when you want to raise the bar in the preserving stakes. I dread to think how many tonnes of fragrant colourful fruit are turned into grim overcooked jam, murky looking and caramel flavoured, packed into jars that smell of last year’s pasta sauce.
Making excellent jam is really achievable at home, and very quick and easy when you get your head around some of the science behind it. Be warned, I’ll shake some of your habits and question some of the laws regarding jam making, but we’ll come out of it better.
There are two women all wannabe jam pros must know about. Yes, women dominate in the jam-making world and I can’t see any men threatening that right now. First up is Pam Corbin, the founder of Thursday Cottage jams and the author of the River Cottage Preserving book. Pam writes with good sense and is someone I always trust in jam matters. The second guru is Christine Ferber, the queen of soft-set fragrant preserves (jam seems too coarse a word here). Her books are great for ideas about combining fruit and maintaining their delicate fragrances.
The best fruit for making firmly set jam is slightly under-ripe, not fully ripe. The setting chemical pectin as a substance that decays as the fruit ripens, even in fruit traditionally rich in it. Under-ripe fruit has the most pectin, but less fragrance and a subtler flavour. You can use fully ripe fruit, but be prepared for the set to be very soft or for there to be no set. The possible set of the jam is primarily determined by three things: the pectin, the sugar level and the acidity:
- Pectin: pickleandpreserve.co.uk has a good list of the fruits that are high or low in pectin. If you’re unsure, assume your fruit is low in pectin and will need some help.
- Sugar: you want enough sugar to give a good set without masking the natural sweetness of the fruit. As the liquid evaporates the percentage of sugar in your jam gets higher, so make sure your cooked fruit contains very little liquid when you add the sugar in order to keep the boiling time short.
- Acidity: adding lemon juice activates the pectin set. Even when fruits are tart and pectin-rich, like blackcurrants and gooseberries, lemon juice or citric acid is often needed to create the set. It’s usually added with the sugar or later - not when the fruit is first cooked as this will firm the skins and give a coarse texture.
Don’t be afraid to add pectin if your fruit needs it. Though pectin is a chemical, not all additives are unnatural. The pectin we buy is usually extracted from apples or limes, and it will help you keep the cooking time short which helps the colour stay bright and the flavour clean and sharp. There are other ways to add pectin. I use Pam Corbin’s tip of grating Bramley apple in with the fruit for a firm set, or pear for a softer set.
Most fruit needs to be cooked once before the bulk of the sugar is added to soften the skins and extract the pectin for a smooth set jam. Even strawberries benefit from slight cooking first. However, some jam makers like Christine Ferber and Sophie Grigson encourage soaking the fruit overnight with some of the sugar so that it releases liquid. This syrup is then precooked. This method is really good for extracting subtle flavours from the fruit and keeping the skins slightly firmer to retain their texture.
Cook the fruit in just enough water so that when the skin or peel is soft there is only a little liquid remaining. This will help your jam to cook quickly to a set, preserving the colour and flavour. Finally, to skim or not to skim? That is the question! I only skim my jam at the end if there is a lot of white foam left, but usually I don’t.
I’ve written a special small batch of jam recipes for BBC Food, combining some of my favourite flavours. Experiment with these and do swap ingredients to your taste. And let us know your tips, or anything you want to question me on.
Dan Lepard is a food writer for the Guardian and a baking expert.