Sunday, August 14, 2011

Plum & Blackberry Preserve

Sheesh, I think I have had too much free time on my hands recently. I cannot otherwise explain why I decided to have a go at preparing homemade jam. I have never tried my luck before, but I do have knowledge and experience of biochemistry. Besides, if generations of Andalucíans can prepare delicious marmalade ...

Before the idea had properly taken hold, my partner saw me coming: she asked if we could ‘do it together’, evidence enough that she did not trust me with the Compact Domestic Incinerator, or ‘cooker’ for short. Unfair, I thought, despite my occasional use of the smoke detector as an oven timer.

The fruit came free. Some friends of mine, on holiday for a week, had asked me to mind their garden, which is not much smaller than a football pitch. Dominating one corner is a huge wild plum tree, much of its fruit almost ripe. With permission, and assisted enthusiastically by my young sons, I collected a couple of kilos (Figure 24.1) without even progressing to the branches out of their reach. (It is not wise to wait too long to harvest plums, as damaged fruit attracts wasps galore.)

Figure 24.1: Wild plums, freshly picked but not quite ripe

Copyright 2011 Paul Spradbery

Later, my partner and daughter helped me pick a comparable mass of blackberries (Figure 24.2) from a local valley. The only drawback was the presence of small grubs, some crawling along the surface, others doubtless submerged and filling their faces. These are raspberry beetle (Byturus tomentosus) larvae, which are commonly found among many soft summer fruits.

Figure 24.2: Wild blackberries, fully ripe but crawling with larvae

Copyright 2011 Paul Spradbery

Back at home, we stoned the plums but did not have the patience the peel them. No matter, we thought. All we needed, now, was a recipe. After trawling through various web pages, I decided on the following proportions of ingredients:

625 g (almost ripe) wild plums
900 g (ripe) wild blackberries
2 kg castor sugar (with incorporated pectin)
165 ml water
125 ml lemon juice

Instructions: Place all the ingredients together in a large pan on medium heat. Stir continuously, while also squashing the lumps of fruit with a potato masher. Bring the mixture to boil for one minute. Remove from heat and allow to cool. Skim off surface foam layer. Pour into sterilized jars, leaving 1 cm space at the top of each. (Use a sieve if seedless jam is preferred.) Replace jar lids loosely and boil in water for 10 minutes. Allow to cool to room temperature. Tighten lids and refrigerate.

We found that, after filling the jars, the seeds settled at the top. We had evidently not allowed sufficient cooling time before pouring. Instead, therefore, we sealed the lids and inverted the jars a couple of times to remix.

Incidentally, pectin (polygalacturonic acid) is an apple-derived polysaccharide which reacts with sugars to produce jelly. This occurs only when heated. Fruits such as plums and blackberries have relatively low pectin concentrations, so extra quantities must be added. The incorporation of lemon juice is to reduce pH (i.e. increase acidity) and thus further promote gel formation. Plums and blackberries lack organic acids, which are weak anyway, so this measure is equally essential.

We ended the day feeling pleased with ourselves (Figure 24.3). The jam was as tasty as the recipe was idiot-friendly. You might be wondering, though, what happened to all the beetle maggots. Well, I figured they were unlikely to survive boiling, so, in a fashion, the jam became ‘fortified with protein’. ¡Buen provecho!

Figure 24.3: Wild fruit pickers!

Copyright 2011 Phoebe Spradbery

Plum-and-blackberry would appear to be an unusual combination. An alternative – and more refined – recipe, devised by a far better ‘kitchen biochemist’, can be found at:

Copyright 2011 Paul Spradbery

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