Witch’s Brew
A Witch’s Brew is 45ml of London Dry gin and 20ml of butterfly pea flower syrup, stirred with ice for 20 to 30 seconds and strained into a chilled coupe. It sits deep blue. At the table, 20ml of fresh lemon juice and 15ml of elderflower liqueur are poured in from a small jug, and the drink turns violet. About 2.1 UK units. The change is chemistry. The University of Florida’s IFAS Extension says the anthocyanins in butterfly pea flowers change colour with pH, and that lowering it with a mild acid such as lemon or lime juice shifts the extract from blue towards pink or light purple. The lemon lowers the pH, and the colour follows. It is a Halloween drink, and the trick needs nothing in the glass but the drink. No dry ice: it burns if swallowed, and fog belongs in a separate container beside the punch bowl, never in a glass.
Glassware: Coupe Glass
Garnish: None: the colour change is the theatre
Ingredients
45ml
London Dry at 40% ABV. Juniper keeps the drink from tasting only of sugar and flowers once the lemon and elderflower land.
20ml
Blue at rest, violet once acid arrives, with almost no flavour of its own. The house syrup: 1:1 by weight, about 2g of dried flowers steeped ten minutes; we keep it a week refrigerated.
20ml
Squeezed the same day, and poured at the table. It is the acid that turns the colour.
15ml
At our working figure of 20% ABV, which is St-Germain’s figure on an LWC listing. It goes in with the lemon and rounds its sharpness with a floral sweetness.
Instructions
Chill a coupe.
Stir the gin and butterfly pea flower syrup with cubed ice for 20 to 30 seconds.
Strain into the chilled coupe. The drink will sit deep blue.
Mix the lemon juice and elderflower liqueur in a small jug and keep it cold.
At the table, pour the jug slowly into the drink and let the colour move from blue to violet.
Stir once to settle.
Our version
Our own Halloween serve: 45ml gin and 20ml butterfly pea syrup stirred blue, with 20ml lemon and 15ml elderflower liqueur poured at the table to turn it violet. No published original.
Source: our own specification. Last checked 10 October 2026.
Expert Tip
Keep everything cold. The blue stage, the citrus jug and the coupe should all come from the fridge or the freezer; a warm pour turns the violet muddy. Pour the lemon slowly over the surface. The colour sinks through the glass in a band and takes a few seconds; tipped in at once, it changes before anyone is watching. Check every mixer for acid. Tonic water, most fizzy drinks and some alcohol-free spirits contain citric acid and turn the syrup violet before the lemon arrives, which spends the trick early.
Behind the Witch’s Brew
Flavour Profile
A Flower That Works as an Indicator
Butterfly pea flower is brewed across South East Asia as a blue tea. Its colour comes from anthocyanins, the pigment family that colours red cabbage and blackberries; the University of Florida’s IFAS Extension names delphinidin as the main one in butterfly pea flowers and says its forms change with pH.
In gin and sugar syrup there is nothing acidic, so the drink stays blue. IFAS Extension says lowering the pH with lemon or lime juice leaves more of the red form, so the extract looks pink or light purple. More lemon gives a pinker glass; the 20ml here lands on violet.
Two Pours, One at the Table
The blue stage is stirred, not shaken, because it has no juice or egg to mix and a clear glass shows the change better than a cloudy one. It should arrive looking finished: still, blue and cold.
The lemon and elderflower wait in a jug beside it. Pour slowly over the surface, where the drinker can see it, and the colour sinks through the glass in a band before one stir settles it.
Keep the Fog Out of the Glass
Halloween tables often use dry ice for fog. It never goes into this drink or any other glass. The British Compressed Gases Association says carbon dioxide pellets in drinks have caused serious injuries, with burns from ingestion. If you want fog, stand a punch bowl inside a larger container of dry ice and warm water, as for our Cauldron Punch, and handle it with insulated gloves and tongs.
The Gin Version and the Alcohol-Free One
The Witch’s Brew with gin and without
Base
- With gin
- 45ml London Dry gin
- Alcohol-free
- 45ml non-alcoholic gin alternative with no citric acid
Blue stage
- With gin
- 20ml butterfly pea syrup, stirred
- Alcohol-free
- 20ml butterfly pea syrup, stirred
Table pour
- With gin
- 20ml lemon, 15ml elderflower liqueur
- Alcohol-free
- 20ml lemon, 15ml elderflower cordial
Colour
- With gin
- Blue to violet
- Alcohol-free
- Blue to violet
UK units
- With gin
- About 2.1
- Alcohol-free
- None
| Element | With gin | Alcohol-free |
|---|---|---|
| Base | 45ml London Dry gin | 45ml non-alcoholic gin alternative with no citric acid |
| Blue stage | 20ml butterfly pea syrup, stirred | 20ml butterfly pea syrup, stirred |
| Table pour | 20ml lemon, 15ml elderflower liqueur | 20ml lemon, 15ml elderflower cordial |
| Colour | Blue to violet | Blue to violet |
| UK units | About 2.1 | None |
How to Serve It
One glass at a time, poured in front of the person drinking it. Label the alcohol-free glasses, because the two versions look the same.
For a Halloween bowl with the fog kept outside it, make a Cauldron Punch; for gin and elderflower without the trick, an English Garden.
Make it at home
The Spirit
GinGin is a spirit flavoured with juniper berries. Under the retained Regulation (EC) 110/2008, juniper must lead the taste, the floor is 37.5% ABV, and the route the flavour takes sets the grade: plain gin, distilled gin or London gin. Our recipes count it at 40%, and it carries the Martini, the Negroni and the Gin and Tonic.
More to explore
Frequently Asked Questions
What is in a Witch’s Brew?
Why does the Witch’s Brew change colour?
Can I put dry ice in it?
Can I make an alcohol-free Witch’s Brew?
Where do I get butterfly pea flowers?
Can I make it ahead for a party?
How strong is a Witch’s Brew?
Sources.
Correct as of 19 October 2026.
- UF/IFAS Extension, “Butterfly Pea (Clitoria ternatea) Flower Extract (BPFE) and Its Use as a pH-Dependent Natural Colorant” (university extension publication: delphinidin the main anthocyanin; blue-purple at normal pH; lowering the pH with lemon or lime juice gives pink or light purple).
- Flinn Scientific (hosted by the NISE Network), “Material Safety Data Sheet: Carbon Dioxide, Solid (dry ice)” (safety data sheet: extremely cold (-78 °C), damaging to skin and tissue; skin contact may cause frostbite and blisters; melting point -78.5 °C (sublimes)).
- British Compressed Gases Association, “Gas abuse” (trade body: carbon dioxide pellets in drinks have caused burns to mouths and internal organs).
- LWC, “St-Germain 70cl” (UK wholesaler listing: 20% ABV).
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Where this one sits
Recipe by Jerry Can Spirits · Updated 19 October 2026