BLACK BOSHI | Preserved Fruit, Berries, and Currants #9
Applying Japanese Boshi Technique to Local Ingredients
Hi,
It’s that time of year when so many ingredients are ripe and ready to harvest that I had to write an extra newsletter this week, one sharing an incredible technique from Japan called umeboshi, that I’ve adapted from the original apricot/plum recipe to a semi-curing for berries and currants. For my readers across the pond, I’m told that blackcurrants aren’t really that popular, but they are available to grow and well suited to areas within your climate (and the currants, fresh young leaves, and twigs are delicious in a variety of culinary applications). If I can’t persuade you to grow blackcurrants, fear not, this recipe works very well with strawberries, red currants, gooseberries, blueberries, and all sorts. Simply swap out the blackcurrants for your berry of choice in a 1:1 exchange.
Introducing Blackcurrant Boshi | 黒スグリ干し
On the surface, this technique couldn’t be more simple. Mix fruit with 18% salt. Yes, 18%*. Whilst this might seem like a huge amount of salt, it’s important for the curing and preservation of this process. The two products made from this process are potent, packed full of flavour, sour, salty, fruity, and funky. One is a salty vinegar substitute that tastes like blackcurrants on steroids. It’s such a concentrated flavour that very little is needed to completely transform your cookery. A few drops in a sausage casserole ignite it with a subtle sweetness, seasoning, and a balanced tartness that elevates the savoury flavours of the dish. Add just a little to sweets such as fruit tarts, ice cream, and anything chocolaty and it gives depth and a lively, playful funk, whilst the salt fulfils a similar role to salted caramel.
On the other hand you have the fruit, which from what I can tell, seems to be the most celebrated component of the original recipe. Cured and seasoned by the salt, it is then sun dried (or gently dehydrated) for 3 days, which alters the texture from a soft, juicy berry or currant, to a firmer, more meaty texture. The flavour remains salty and acidic, with a punchy, concentrated version of its fresh counterpart. The fruit is then stored for 4-6 months, ageing, and allowed to develop. During this time, the saltiness diminishes somewhat, and the flavours become more complex, much like wine. These little gems of flavour can be crushed into sauces, hidden away within dumpling filling, or mixed into a paste and used to marinade vegetables, meats, and seafood.
Both can also be used as condiments in their own right, like soy sauce and dipping vinegar.
* For umeboshi, it is possible to make a low sodium version using 15% salt instead of the traditional 18%, however, the finished product will require refrigeration.
The Health Benefits of Umeboshi
There are a wide range of health claims surrounding umeboshi, some of which stem from the properties of the fruit itself (so will differ depending on the version we are making), others are derived from the process. These benefits are rooted in both traditional usage and emerging scientific research, though more large-scale studies are needed to confirm certain effects. Where I can, I’ve listed sources to the information below as a footnote to this newsletter, but until conclusive research is published, please always take this kind of information with a pinch of salt.
1. Digestive Health
Umeboshi contains citric acid, which stimulates saliva production and gastric juices, aiding in digestion and preventing indigestion. It also has traditional uses in combating bacterial infections in the stomach and intestines, promoting a healthy gut environment.
2. Antioxidant Effects
It is packed with antioxidants, particularly polyphenols, which help neutralise free radicals, reducing oxidative stress and inflammation in the body.
3. Alkalizing Effect
Despite its sour taste, umeboshi is considered an alkalizing food. This helps balance the body's pH by reducing acidity, which may be beneficial for overall health. Foods that promote a balanced pH in the body can aid in reducing the risk of chronic diseases such as arthritis, osteoporosis, and more.
4. Detoxification
Umeboshi is believed to support liver function and detoxification, as it is often used to help reduce hangover symptoms by promoting liver activity. Studies specifically on umeboshi’s detoxifying effects are limited, but anecdotal and traditional use suggests it helps in eliminating harmful substances from the body.
5. Boosts Immune Function
The citric acid content in umeboshi can stimulate production at the cellular level, improving immune responses. Its high antioxidant levels also contribute to overall immunity, with research showing that umeboshi extract might inhibit viral infections and improve immune response, although more specific studies are needed in this area.
6. Bone Health
Some studies suggest that umeboshi may have potential benefits in preventing bone loss, especially for menopausal women, due to its ability to balance the body's pH and provide antioxidants.
7. Fatigue Relief
The high concentration of citric acid in umeboshi can help reduce fatigue by promoting metabolism and eliminating lactic acid buildup in muscles after strenuous activity (or a long day gardening!)
8. Antimicrobial and Antiviral Properties
Umeboshi is traditionally used as a preservative and is believed to have antimicrobial and antiviral effects.
9. Improves Oral Health
The antibacterial properties of umeboshi may help reduce bacterial buildup in the mouth, which can prevent cavities and promote oral health. However, its high salt content, if eaten in regular, large amounts, can cause cellular damage and inflammation to digestive organs (as is the case with all high salt foods).
Now that you’re familiar with what we’re going to make, and have some initial ideas for the versatility of uses it boasts, let’s jump straight into nerdy stuff.
Not All Salt is Created Equal
It’s important to use a coarse sea salt, as is the case with traditional garum too. It dissolves slowly as it extracts juices, gently drawing moisture from the ingredients, whilst providing a uniform distribution of salinity. This slower rate curing process preserves a firmer texture, which fine salt can ruin, drawing water out too quickly and making fruit mushy. It is also typically higher in natural minerals compared to refined salt, such as magnesium and calcium, which contribute subtle flavours and enhance the nutritional profile of the final boshi. The slow dissolving rate also provides a window for microbes to ferment in before higher levels of salinity bring it to a halt, shifting the process from active fermentation to ageing. And finally, for those who might be new to fermentation or this style of salt preserving, the salinity level is what gives this product its preservative qualities. Without the correct amount of the right kind of salt, umeboshi is rendered useless, or worse, dangerous. So make sure you weigh carefully, and follow the steps as I’ve written them below.
I often receive a lot of comments on Instagram saying that I waste good salt when I should use a fine salt, or even a table salt. But there is always a reason for the methods I use, and table salt in particular is bad for such processes (and, in my opinion, bad for food in general), as it is fortified with iodine, which can inhibit the growth of beneficial bacteria.
BOSHI | Full Technique
This technique is very simple but takes time. There are a couple of details I’ll highlight that make a big difference to the final products.
Ingredients:
800g berries, currants, or stone fruit
144g coarse sea salt
Optional:
100g red shiso leaves
18g salt
Equipment:
1.5L glass jar or crock
Baking parchment
Glass or ceramic weight*
* If you don’t have a pebble weight, use a spare jam jar that’s small enough to fit inside the main jar. Fill it with grain and secure the lid, then place it the right way up on top of the baking parchment to provide a weight to the top of the ingredients. This method is a great option for all ferments that require weighing down and is much cheaper than buying glass or ceramic weights.
Rinse the currants in cold water and spread them out on a clean kitchen towel to dry off.
Weigh out the salt, then add the currants and salt to the jar one layer at a time, alternating between them to make sure the salt is evenly distributed throughout the currants. If using stone fruit, remove the wooden stem but don’t cut the fruit. Add them whole to the jar along with the salt.
Cut out a round piece of baking parchment that is big enough to cover the surface of the currants. This will help trap the currants under the weights and stop them from floating when liquid releases.
Place the glass or ceramic weights on top of the parchment. These need only be 10-30% the weight of the contents of the jar, which is ample to weigh everything down without crushing the integrity of the ingredients.
Seal the jar and leave it somewhere between 15-21°C (59-70°F) for a month. During this time there may be a small amount of activity that produces carbon dioxide, but as the salinity raises it won’t amount to much, therefore the jar won’t need regular opening like in lacto fermentation.
After a month has passed, for traditional umeboshi (using the Japanese plum), red shiso comes into season and is used to infuse flavour and imbue colour. If you would like to do this too, remove each shiso leaf from the stem, then mix them in a large bowl with half of the additional salt listed in the ingredients above. Massage it in for 1-2 minutes, as though making sauerkraut. This will draw out a grey-pink foam that should be discarded before adding the remaining salt and adding the shiso to the boshi jar. Note, if using red shiso, this plant has a powerful ability to stain, so you may wish to wear gloves. If you are making berry or currant boshi you can skip this step, but including it does add an extra layer of flavour and aroma.
Traditional umeboshi with red shiso Continue to age for a further 2-3 weeks and keep an eye on the weather forecast. You’re looking for 3 days of sunny weather back-to-back. As it is, the boshi can wait extra months if required. If you live somewhere, like me, where this is a rare event, you can use a dehydrator set to fan only, but I’d advise you start the process off on a sunny day at least. The UV light helps blast the microbes on the surface of the currants, preventing mould from growing.
To dry the boshi, pass the liquid with a fine mesh sieve and bottle it. Collect the currants or fruit and spread them out over a fabric tea towel, fine mesh tray, or traditionally, a flat bamboo basket. Place them in direct sunlight with good airflow. This can be beside an open window, or outside (but you may wish to cover them with a fabric cloche to keep insects off them). Turn them once a day to give even exposure to the elements and make sure they’re dried evenly.
If the weather acts against you, use a dehydrator set to fan only for 2 days. This will help preserve the boshi but won’t provide the exact same texture. It won’t be far off though.
When done, the currants or fruit won’t be crispy like other dehydrated ingredients, rather, they will have a tacky feel but still hold moisture. Internally, they will firm up a little, producing a meaty texture in stone fruit, and a soft, pliable texture in currants and berries.
When finished, you have two options for storage: the first is to keep the fruit as they are in an airtight container somewhere cool and dark. Like this, they will remain preserved for several years. Or, you can add a little of the brine (umesu) back into the container with them. Now they’ve been dried, they partially take on the liquid again, enhancing their flavour in a more sour, punchy way.
Either way, boshi gets better with age. I leave mine for 6 months minimum before eating them, as the flavour develops like a fine wine. The saltiness diminishes somewhat and sourness develops a more rounded complexity.
And that is how I made boshi from strawberries, blackcurrants, gooseberries, and of course, apricots / plums. Within this incredibly simple technique there is so much room for creativity. Try swapping the shiso for another herb, or add aromatics like ginger root. You can also replace some of the salt for a coarse smoked salt, infusing the fruit with a smokiness that compliments savoury meals beautifully.
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Footnotes and sources:
A study published in the Bioscience, Biotechnology, and Biochemistry journal indicated that ume extract has antimicrobial properties, especially against Helicobacter pylori, a bacterium linked to stomach ulcers and gastritis. https://pubmed.ncbi.nlm.nih.gov/14519964/
A study in the Journal of Agricultural and Food Chemistry highlighted the antioxidative properties of polyphenolic compounds found in Japanese plums, which are similar to ume. https://pubmed.ncbi.nlm.nih.gov/16190607/
Though direct studies on umeboshi's alkalizing effect are limited, general studies on alkaline foods, such as those published in the Journal of Environmental and Public Health, support the idea that alkaline-forming foods can benefit health. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3195546/
One study on Japanese ume fruit suggested that its consumption might suppress bone resorption in postmenopausal women. https://pubmed.ncbi.nlm.nih.gov/16446268/
The antimicrobial activity of ume extract against H. pylori and other bacteria has been documented in several studies. https://pubmed.ncbi.nlm.nih.gov/14519964/
A study published in the Journal of Agricultural and Food Chemistry supports the role of plum extracts in reducing oral bacteria. https://pubmed.ncbi.nlm.nih.gov/16190607/
I just want to say thank you so much for taking all of the time to research and prepare these incredible posts. They are such an amazing resource to have access to ❤️
Fascinating as ever Sam. I have some umeboshi gooseberries from 3 years ago that it's occurred to me I'm leaving as a project in 'how long exactly will these stop tasting so good/when will they kill me?'!