Cold brewing suits Thai botanicals unusually well. Without heat you extract the aromatic compounds and very little of the coarse, woody ones, so the result is cleaner, sweeter and almost impossible to make bitter. It is also the least demanding method there is: put leaf in water, put it in the fridge, forget about it.
The basic ratio
5g per 500ml of cold water, 8–12 hours in the fridge. That is roughly double the leaf you would use hot, because cold water extracts far more slowly.
Use cold water from the start — not warm water left to cool. Strain when it is ready; leaving the botanicals in for another day will not ruin it, but it stops improving after about twelve hours.
Which ones are worth it
- Pandan — excellent. The grassy note recedes and the vanilla-like sweetness comes forward. Probably the best cold brew in the range.
- Lemongrass & pandan — excellent, and much harder to over-extract than hot, which is where lemongrass usually goes wrong.
- Peppermint — very good. Cold brewing keeps the menthol bright rather than steamy.
- Roselle — good, and noticeably less aggressively tart than hot-brewed. Deep red, excellent over ice.
- Butterfly pea — the colour develops just as well cold. Add citrus at serving for the colour change.
- Rose, chamomile, osmanthus — workable but you lose some of the delicate top aroma that heat releases. Hot is better for these.
The one that will not work
Stevia leaf does not cold brew. Cold water does not pull the sweet compounds out of the whole leaf in any useful amount, so a cold brew with stevia in it comes out grassy rather than sweet.
If you want a sweetened cold brew, make a small strong stevia infusion in hot water first, let it cool, and stir that in to taste. Same for sugar — dissolve it in a little warm water rather than trying to stir granules into a cold jug.
Practical notes
- Strain properly. A fine mesh strainer matters more here, because fine fragments that sit in the jug will keep extracting and eventually turn it cloudy.
- Keep it 3–4 days in the fridge, covered. It is not sterilised, so treat it like fresh juice rather than something shelf-stable.
- Do not add citrus until serving. Lime in the jug from the start dulls over a day; added to the glass it is bright, and with butterfly pea it is the whole trick.