Yarrow in Mead Making
Yarrow (Achillea millefolium) has a long history of use as an herb, Yarrow had cultural significance for the Vikings and was considered a sacred herb. It was associated with the god Odin and the goddess Freya. The Vikings held yarrow in high regard and incorporated it into their customs and practices.
In addition to the cultural significance was of course its use a herbal remedy where it was used to treat wounds and a myriad of other things.
The entire plant is edible, and it is said that the leaves are best harvested when the plant is in bloom. It is much like Marjoram at this point where the flavour is well spread through out the blooms and leaves. If picked before bloom there is more flavour within those leaves, try it. Come to your own conclusion with this one.
If used in secondary, fresh Yarrow brings a herbal bitters flavour that is described by many as being like peppery licorice or anise. Some also find strong notes of tarragon. It can be bright and bold in its presence. It can also be overpowering.
If used as a dry herb it loses a lot of its brightness, it has less tarragon freshness to it but do not let this stop you from using it, even as a dried herb it is a brilliant ingredient to have in your cupboard.
If steeped in heat it may become bitter quickly, I use it without heat. It seems to have a tannin extraction temp around the mid eighties (celcius), keep it below that if you must use heat and wish to avoid extra bitterness.
If left in for secondary for too long the flavours become grassy, there is a bit of time between giving a lot and hitting the notes of grass, but it is worth finding that gap and retrieving the Yarrow.
Having said this: a mead that has gone grassy and aged clean has a different note to one that never went grassy at all. It is not an unpleasant note, though also is not everyone's favourite and it takes some time in ageing to achieve.
If used in primary (and a fair bit of it) it brings a lot of flavours that change as the yeast do their bit with it. It takes some time for these flavours to mellow, but they do and Yarrow brings a herbal complexity to any big and bold flavoured mead when used like this.