It has been an exceptional year for wild fruit of all kinds and British hedgerows are painted crimson by hawthorn berries, with splashes of purple-black where the sloes hang in succulent bunches. Sloes are, of course, the fruit of the blackthorn tree (Prunus spinosa) and are perfectly edible. In fact blackthorn is one of the progenitor species for cultivated plums. In Britain we tend to associate sloes with sloe gin. But, if you follow this link, you’ll see that there are lots of other edible uses for the fruit. However sloes are notoriously astringent so they need to be processed in some way before they are palatable.
The mention of umeboshi plums in that section of the Wikipedia article got me thinking because it chimes with things that I have been reading in the new book Fermentation by Rachel de Thample. As I mentioned in this post on sourdough bread from a couple of years ago, I have a longstanding interest in fermented foods and drink that goes back to my time working in a brewery in my home town of Sunderland.
Fermentation talks a lot about lacto-fermentation in which salt is used to prevent the growth of “bad” fungi and bacteria and promote the growth of Lactobacillus. These “good” bacteria then ferment the sugars in fruit and vegetables, releasing lactic acid and increasing the edibility and digestibility of the foodstuffs. Sauerkraut is a good example of this process in action. As well as salt you have to exclude air to make the process at least partially anaerobic.
After a bit of reading I experimented with a basic recipe to lacto-ferment sloes to turn them into something resembling the flavoursome wonders that are umeboshi plums. And do you know, it worked! Lacto-fermenting the sloes transforms their flavour from mouth-puckeringly astringent to sour-and-salty.
Here’s the procedure:
Pick your sloes before they are frosted, discarding any that are shriveled or have been damaged by insects or fungi. Immediately wash them to get rid of any dust and rescue the spiders and other invertebrates that are bound to be flushed off! Put the sloes to one side.
Wash and rinse a glass jar with a tight fitting lid, which is equal to the capacity of the sloes but no more, i.e. you want the sloes to fill it to the top. Sterilisation shouldn’t be necessary as the conditions inside will not be suitable for growth of anything other than the Lactobacillus. But it’s best to rinse out any detergent.
Weigh the sloes and then weigh enough fine sea or rock salt to equal 8% of the weight of the sloes. In other words, for every 100 grams of sloes, you need 8 grams of salt*. Don’t use standard table salt as it usually contains chemicals of various kinds.
Add about a quarter of the sloes to the jar and then sprinkle in a quarter of the salt, put the lid on and invert it a couple of times to distribute the salt. Add another quarter of sloes and salt and invert again. Repeat until you have filled the jar with sloes and salt.
Put the lid on tightly, write the date on the jar or on a label, and put in a cupboard or shelf away from direct light. It’s best to stand the jar on a plate to catch any of the liquor that may come out of the fruit.
Invert the jar a couple of times once a day to keep the salt distributed over the sloes. After a few days a purple liquid will start to build up. This is the water from the sloes being drawn out by osmosis. After four or five days open the jar and try one or two sloes. If you like the flavour, put the jar in the fridge to stop the fermentation. Otherwise let them ferment until the flavour suits you.
At the moment I am just snacking on these sloes but I am sure they could be used in recipes that require a salty-sour note. The liquor that builds up in the jar could also be used to flavour dishes or as the basis for a salad dressing.
*8% salt was based on something that I read which I can’t now find and might be overkill. I am going to try it with 2% to 4% salt and see if that works.