The Chemistry of Elderflower & Elderberries

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In late May and early June, the winding pathways of the English countryside are festooned with the delicate white blooms of the elderflower. As the end of the summer eventually arrives, these blooms will have been transformed, and the bushes will be heaving under the weight of clusters of hundreds of small, purple-black berries. In this post, we take a look at the compounds behind the heady aroma of elderflower, as well as those behind that of elderflower, and also examine the claims of toxicity of elderberries.

If you’re a regular reader of the site, then you’ll already know that it’s rarely a single compound that causes a particular aroma. The aromas of elderflower and elderberries are no exception! A catalogue of compounds have been implicated in the scent of elderflowers; the most significant of these are cis-rose oxide (unsurprisingly also found in roses), hotrienol, nerol oxide, and nonanal. A host of other compounds accompany these key chemicals, including linalool and alpha-terpineol (both of which contribute to the floral aspect of the aroma), and hexanal and (Z)-3-hexenol (which add a grassy aspect).

When it comes to the berries, many of the same compounds are still present: linalool, hotrienol, and nonanal have all been identified. The chemicals thought to contribute to the characteristic aroma of elderberries are beta-damascenone (another compound that can also be found in roses), dihydroedulan, and phenylacetaldehyde.

In terms of flavour, elderberries have a rather bitter, astringent taste. They contain a number of fruit acids, with citric acid being the most abundant. Their bitterness and astringency is owed to the high levels of tannins present in the berries. The purple-black colour of the berries is due to the presence of anthocyanins, a class of colour-causing compounds which contribute the colour of many other fruits as well. In elderberries, the most abundant anthocyanin is cyanidin 3-sambubioside.

There are a host of things you can make from elderflower and elderberries. We’ve already made elderflower syrup and elderflower wine this year, and you can make wine from the berries too, as well as jams. Though the flowers pose no harm, it’s worth knowing that the plants leaves and stems, and the seeds of the berries, can cause nausea and general unpleasantness if ingested without cooking.

The reason for this is due to the presence of a couple of compounds. One of these is the cyanogenic glycoside sambunigrin. Cyanogenic glycosides are found in the seeds of numerous other fruits too, including apples and peaches. They consist of a cyanide group bonded to a sugar; when the compound is digested, the cyanide group is freed from the sugar, and can exert toxic effects. The leaves, stems and berries can also contain alkaloid compounds, including the alkaloid sambucine, which are also poisonous.

As some elderflower syrup recipes in particular call for use of the flowers without cooking, it’s a good idea to remove the flowers from the stems beforehand. Toxicity from the juice of raw berries has been reported, but if the berries are being cooked, there is no cause for concern. This is because cooking breaks down the cyanogenic glycosides and sambucine present, rendering them harmless.

If you’re interested in trying out making your own elderflower syrup, the recipe we usually use is here, though it’s in Hungarian which might make it a little tricky for most non-Hungarian readers to follow! I’ve included a translated version below:

Ingredients:

10 kg of sugar, 5 L water, 10-15 g citric acid, 1.5 kg of lemons juiced and chopped, white elderflower heads (about 100). (Obviously this makes quite a lot, but quantities can be scaled).

Method:

Dissolve the sugar in the water in a large saucepan, and start gently heating it on low heat; don’t let it come to a boil or caramelize. Keep stirring and don’t stop for a good 30-40 minutes, until you are absolutely sure that there are no crystals anywhere in the syrup.

Place the unwashed elderflower (if you wash them, you lose the pollen) heads in a pre-sterilised fermenting tub, layered with the chopped lemons.

Let the sugar syrup cool to room temperature and then mix in the citric acid and the lemon juice. Pour this over the flowers, cover it and let it sit in a cool place for about 2 days, giving it a stir every now and then with a sterilised spoon.

Sterilise a big pot, a sieve and a muslin cloth along with a ladle and all of the bottles you’ll be filling up.

Fix the sieve over the pot and place the muslin inside it. Spoon your syrup and flowers into the muslin and let the cordial collect in the pot.

After you’ve got all of your cordial, get a funnel (which should also be sterilised), and fill the bottles up to the top. Keep these bottles in a cool, dry place, and once a bottle is opened, keep in the fridge.

elderflower syrup

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References & Further Reading