from "Living Within" September 2015 (abridged and adapted from earlier blog version)
As summer eases into autumn we have our opportunity to preserve the fruit now abundantly in season. I know you can buy jam in the supermarket, without needing to get your hands and kitchen surfaces sticky, but it is not the same thing at all as that which you can make in your own kitchen. Supermarket varieties are typically top-heavy with sugar and set to the point of rigidity; homemade versions sharpen up the flavours and introduce possibility. Here, I hope to get you started with some basics.
Most fruit can be “jammed”, but I will stick to plums for now; these will be everywhere soon - all sorts of varieties - and damsons, my personal favourite for jam, will disappear almost as soon as you first see them (if you are lucky enough to find any in the first place). Plums make great jam, damsons make the best jam of any fruit that I know, but I won’t pretend that they can’t be a massive faff - they are small and fiddly and time consuming, and sometimes wormy. Nigel Slater believes that it is masochism to stone a damson before you cook it, maybe especially for the quantity that you will need for jam, and there is talk amongst experts of how there is no real need - pits obligingly bobbing to the top of the jam pan to be relatively easily skimmed away after the jam is cooked. But I think these experts may be telling half truths - not about the masochism aspect - it is a truly painstaking process to pit damsons (and will take about an hour per kilo) - but about the ease of managing the pits post cooking, especially if you want to be sure of the safety of your consumers’ teeth. I also confess that I ignore their possibly wise counsel and take the time to pit them all before I start.
Jam making is not particularly complicated, but it does involve science, and it is shrouded in a bit of mystery and specialist language. You need to know what is meant by a “set”, although some cooks also express preferences for “their” set, which can give a degree of leeway for when setting is proving difficult - a “soft” or “loose” set may be preferred to the “firm” version found in industrial varieties, and it may be a way of forgiving yourself for when your jam is looking a bit runnier than the kind that will win prizes (for perfectionists and experts it’s definitely not only about flavour).
You will also need some equipment: an appropriate large pan - preferably one with outward sloping sides (not a necessity, but it speeds up the process); jam jars (sterilised ones) plus suitable lids; a thermometer can give a degree of security but is not a necessity either; saucers; teaspoons; a freezer shelf; a suitable stirring spoon (wooden, silicone or metal but, importantly, one that has no taint of anything like an onion lingering on it); a sharp edged skimmer, and a ladle. Finally, you will need to find a quiet time of day and a measure of patience.
The ingredients are worked out in ratios - roughly speaking, for plum jam (any variety) these can translate to 1.2kg of fruit (approximate net weight after stoning will be 1kg) to 800g sugar (granulated, white), and the juice of a lemon; you can scale up the quantities, but it is often easier to make several small batches than to attempt one large one.
Check your fruit - it should be ripe but firm and have no significant blemishes or mould. Wash, halve and pit (big plums are typically easy, small ones not - use a small sharp knife to help coax pits from flesh). Layer the fruit with the sugar in a large bowl and add the lemon juice (it will prevent the cut fruit from browning, and stop you from forgetting to add it later). Cover closely with cling film, and leave to macerate - an hour will do if you are pushed for time, 24 hours is about your limit. Meanwhile, prepare you jars and put a small stack of saucers and a few teaspoons into your freezer.
Transfer fruit and sugar to your (scrupulously clean) large pan - put it on a gentle heat and stir occasionally until ALL of the sugar has dissolved in the juices. Turn up the heat and start to boil the jam vigorously. Continue stirring occasionally (to distribute the heat evenly and to stop the jam from “catching” or burning on the bottom of the pan. It will take about 10 minutes of vigorous boiling for the jam to reach setting point(technically, this should be when it reaches about 105ºC - in real life, for all sorts of reasons, the temperature registering may not indicate the jam is there just yet, so… take the pan off the heat, take out one of your saucers and spoons, dip the spoon into the jam and let a drop of jam fall onto the saucer. If the jam spreads into a liquid it is not set, if it forms a neat pert bead that will wrinkle slightly if you push it, it is. If it is not set, you need to repeat this process every few minutes until it is. As the jam calms itself down, skim off any scum that is left at the surface and discard. Leave the jam for a few minutes to cool and settle, but while it is still hot, ladle it into the jars, seal, allow to cool, and store until later; enjoy at will over the coming months.
“That’s why I hate to get started in these jam sessions. I’m always the last one to leave.”~ Elvis Presley