Costmary (alecost): how to use this mint-scented leaf, and when not to

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Costmary, also known as alecost or Bible leaf (Tanacetum balsamita), is a hardy perennial with long grey-green leaves that smell of spearmint and taste distinctly bitter. This page covers what the leaf actually is, what herbalists and old kitchen tradition make of it, how to brew it, how to use it in cooking, and who should leave it alone.

What it is credited with

• Traditional European herbalism classes costmary among the bitter digestive herbs, taken after a heavy meal for a feeling of fullness.
• It has a long-standing reputation for easing trapped wind and bloating, in the same family of uses as mint and tansy.
• Herbalists describe the leaf as antispasmodic, and it was traditionally taken to soften a tickly, spasmodic cough and to settle gripey cramping in the gut.
• Old herbals list it as a diuretic plant, used when the body feels waterlogged and heavy.
• Country tradition used costmary infusions as a vermifuge, a practice now largely abandoned and not one to attempt at home.
• Applied externally, the leaf macerated in oil has a folk reputation for soothing small grazes, superficial burns, stings and insect bites.
• Dried leaves were tucked into linen cupboards as a moth-deterrent and scenting herb, and into books as a bookmark that perfumed the pages.

How to use it

The infusion

• Use a small handful of fresh leaves, roughly torn, or about a teaspoon of dried crumbled leaf per cup.
• Pour water just off the boil over the leaf, cover the cup, and leave to steep 5 to 10 minutes.
• Covering matters: the aromatic compounds are volatile and escape with the steam.
• Strain well. Expect a clear, minty-smelling brew with a firm bitter finish.
• Traditionally taken after the evening meal, one cup, and not more than two cups in a day.
• Costmary is used in short runs — a few days to a week — rather than as a daily habit.
• A little honey or a slice of lemon takes the edge off the bitterness without masking the mint.

The oil macerate

• Dry the leaves fully first: any moisture left inside will spoil the oil.
• Pack a clean jar loosely with dried leaves and cover completely with olive oil.
• Seal, stand on a sunny windowsill for three to four weeks, and shake the jar every few days.
• Strain through muslin, bottle in dark glass, label and keep in a cool cupboard.
• Used externally only, dabbed on unbroken or barely grazed skin. Never on a deep, dirty or open wound.

In the kitchen

• Treat it like mint, but with a far lighter hand — two or three chopped young leaves are usually plenty for a dish for four.
• Young spring leaves are the mildest; older summer foliage turns coarse and much more bitter.
• Classic pairings: mixed salads, green peas, new potatoes, vegetable soup and beef stew.
• A single shredded leaf lifts a fruit salad, which is how children usually meet it first.
• Add it at the end of cooking, off the heat, so the mint aroma survives.

Frequently Asked Questions

The one thing to remember: pick two or three young leaves, steep them covered for 5 to 10 minutes after a heavy meal, and keep it to a short run of days rather than a daily habit.

Does costmary really taste like mint?

It smells like spearmint, thanks to its carvone content, but the flavour is another story. On the tongue it is markedly bitter and balsamic, which is why it is used in small amounts. Young spring leaves are much gentler than tough summer ones.

Which part of the plant do I use?

The leaves, fresh or dried, are the part used in both cooking and herbalism. Flowering tops are sometimes included in infusions. Harvest leaves from late spring to late summer, ideally before the plant flowers.

Can I drink costmary tea every day?

Tradition uses it as an occasional after-meal brew, not a daily drink. Some costmary contains thujone, so short courses of a few days to a week and no more than two cups a day are the sensible frame. Skip it altogether if you are pregnant, breastfeeding or prone to seizures.

How do I make the oil macerate?

Dry the leaves completely, pack them loosely in a jar, cover with olive oil and leave in the sun for three to four weeks, shaking now and then. Strain through muslin into dark glass. It is for external use only, on intact or lightly grazed skin, after a patch test.

Is costmary the same as tansy?

No. Costmary is Tanacetum balsamita, tansy is Tanacetum vulgare — same genus, very different plants. Tansy is considerably more potent and is best avoided. Identify your plant with certainty before harvesting anything.

This information is provided for general interest and reflects the traditional use of plants. It is not a substitute for medical advice. If you are on medication, pregnant, or in any doubt, ask a healthcare professional.