Brewing Bog Myrtle Gruit

 

Bog myrtle, aka sweet gale, Myrica gale

(image Pl@ntnet, Creative Commons)

Brewing gruit is a mysterious art, involving lots of speculation and a frustrating amount of trail and error. I have long been interested in bog myrtle (aka sweet gale, Myrica gale) as a brewing ingredient, and this brew was designed to test its properties and to get a handle on the quantities that should go in, and at which points in the process.

Three native plants are commonly associated with gruit as it was brewed in the UK and northern Europe up to around the 16^th century: yarrow, mugwort and bog myrtle. The first two are easily sourced anywhere in the country, but bog myrtle is more difficult to track down. It likes continuously wet conditions and sandy, acidic soil. My source is a place in Dorset. Bog myrtle has a very distinctive smell, and when you know what to smell for, you can just follow your nose. And when you do find it, you’ll always find lots. My experience in brewing with both yarrow and mugwort has been that discretion is always wise. Both plants quickly overpower, and the results are usually acrid and undrinkable. So I approached bog myrtle with similar caution.

The plant is deciduous, but it has a very strange growth cycle. The flowers appear first, on the otherwise bare stems, and the leaves come later. There may be an argument for getting in early in the spring and just taking those flowers, in order to get a higher proportion of aromatic oils to tannin. But at that stage, the flowers are tiny, and it would take a very long time to pick what you need. I picked mine in September and came away with a mix, mostly of leaves, but with plenty of flowers too.

So what to do with it? I found a recipe in Sacred and Herbal Healing Beers: The Secrets of Ancient Fermentation by Stephen Harrod Buhner (Siris: Boulder 1998, 176). 

A simple process then, with the bog myrtle added at the start of the boil and then for dry hopping (after fermentation, I thought, would be wiser than before). The recipe calls for fresh leaves and berries, and mine were already dried, so that was the first problem. 

 

In fact, the water content of the leaves is already very low, so the 4/1 proportions we assume for wet/dry hops probably would not apply. Another question arises about the difference between adding the bog myrtle at the boil and at the dry hop stage. It would seem logical that the boil addition would impart bitterness (or at least tannin astringency) and flavour, while the dry addition would impart aroma. But there is no isomerisation going on here, so the behaviour of hops is of little help. In the end I came up with the following recipe, for a 50L brew.

12.5kg maris otter

Mash temp: 64°

Boil time: 60 minutes

Additions of dried bog myrtle: 80g at 60 minutes; 40g at 30 minutes; 110g dry hop

Yeast: US05

Initial gravity: 1043

Final gravity: 1012

ABV: 4.1%

As I was trying to accentuate the resinous, aromatic qualities of the bog myrtle, I aimed for a dry malt profile, so a 64° mash-in and the dry-finishing US05 yeast. The bog myrtle went in the wort in bags, so as to avoid having to scoop out all the tiny twigs. I tasted and stirred throughout the boil, increasingly frustrated that the bog myrtle flavours did not seem to be coming through, hence the second addition. In retrospect, I needn’t have worried—the quantities here are more than enough. The dry hop addition sat in the fermenters for a good week or so.

The results are very fine. The gruit has a cloudy, orange appearance, which must come from the bog myrtle, as maris otter alone would be lighter and clearer. The nose has a distinctively ‘boggy’ note. It’s that same smell that the plant gives off, sweet and resinous. The flavour is different. It is peppery and has an edge that balances well against the malt sweetness. 

What is that edge? The issue with all gruit brewing is how to substitute the alpha acid of hops with some other flavour that will prevent the drink from excessive sweetness. Tannin clearly plays a role in this, and one of the great dangers of boiling any gruit herbs is the excess of tannin they give off. But there are other things going on here too. There is an acidic edge to the taste, pleasant but wholly distinct from hop bitterness. In my previous experiments with gruit herbs, I have often added bittering hops, on the grounds that the herbs themselves do not have this property. But there was no need here; hops would only have confused the flavour profile.

Next time round? I’m reluctant to admit, but there is a case for lowering the quantities of bog myrtle. Or maybe raising the alcohol level would produce a better balance. One risk there is that a higher level of malt sweetness might tip the balance against the dry, resinous profile. Another possible direction is the addition of further gruit herbs. Perhaps a small addition of dried yarrow flowers at the dry hop stage. I’ll look into this next year and report back.