Drinking shamrock-colored beer has become just as synonymous with St. Patrick’s Day as pinching people who don’t wear green, or clandestinely texting an ex in the back of the pub at 1am. And while the Irish have a tradition of dropping clovers in drinks for good luck (known as “downing the shamrock”), turning your brew bright green — much like celebrating St. Patrick’s Day with excessive fervor — is a purely American move.

Where it all came from

In 1914, in New York City, a coroner’s physician named Dr. Thomas Curtain took a break from poking dead people to grab a pint on St. Paddy’s Day at the Bronx’s (now closed) Schnerer Club of Morrisania. While there, he used what was most likely a fabric or textile dye to turn the flow of beer green for a day — which, unsurprisingly, became a big hit with the swill-happy crowd. The event was even written about in the Evening Independent, shortly after. And obviously, the rest is boozy, emerald-tinged history.

While most beer-dyers steer clear of Curtain’s original recipe (probably because textile dye isn’t the safest thing to consume), it’s not all about using basic food colouring to get that shamrock shine. In the past decade, some craft brewers have tried to come up with their own green beer recipes, without the aid of traditional dye. In 2005, Delaware’s Dogfish Head Brewery used the protein-rich, blue-green algae spirulina to give their German lager a nice, green sheen. It was just a one-off. Then in 2013, New York’s Captain Lawrence Brewery tried their hand at making a spirulina-infused beer, cheekily calling it “Gimmicky Green.” Which also never really stuck.

But, since most of us don’t have the brewing power to infuse our beers with a protein-rich algae, we have to turn to food colouring at home. And that’s OK. The problem is, most of you are doing it wrong. It has nothing to do with green food colouring (!) Here’s how to dye your beer green, the right way — without toxic dye, spirulina, or green food colouring

The correct way to dye beer green

Select a light beer
If you really want to get a bright, green-coloured beer, you need to buy something light. Apologies to all stout and hazy IPA lovers, but lighter beers will facilitate the colour change much better, and you’ll have a much better-looking result. Given the quantities in which green beer is often consumed, people often understandably keep it economical and reach for low-ABV macro adjunct lagers. However, if you insist on keeping it crafty, you definitely have some options — a crisp pilsener with clarity can certainly facilitate going green as well.

Add this food colouring
Now you are going to need food colouring — but use blue instead of green. This isn’t because the Order of St. Patrick’s official colour is actually blue; it’s because the blue dye will mix with that light yellow hue of the beer you’re pouring to create a brilliant green, which hopefully makes sense if you paid attention in your elementary school art class. If you add green dye to almost any type of beer, you will end up with a dull, swampy colour — much like the Chicago River (in its normal state). It will be fine. It will be festive. But it won’t be the brilliant green you’re looking for.

Add just a couple drops at a time, gradually, to get precisely the colour you’re after.

At the end of the day, green beer made this way should be safe. It should be easy. And it’s definitely fun. We might not know how Chicago turns their river green, but now you should surely know how to dye your beer green at home. Just do us all favour, and drink your green beer responsibly this St. Paddy’s Day.

Wil Fulton is a staff writer for Thrillist. If you told him he could only eat one food for the rest of his life, he’d be frightened and confused. Follow him: @wilfulton.