What Flavor Is the Shamrock Shake?

Today's shake is vanilla reduced-fat soft serve blended with a green mint syrup and topped with whipped cream. There are no mint leaves in it.² McDonald's has not said whether the mint is peppermint or spearmint. It sells the shake for a few weeks around St. Patrick's Day.

What was the original?

The early history is genuinely mixed up. Here is what the published accounts say, and where they disagree.

Some accounts say Rosen's 1967 shake was mint, the 1970 launch went lemon-lime in some cities, and mint came back in 1983.¹ Others describe the lemon-lime sherbet shake as the original recipe. McDonald's and Rosen's son have said it was minty from the start.

We could not find a primary document, such as a 1970 recipe card, that settles it. What is clear: mint has been the flavor since 1983.

Why it tastes the way it does

Mint flavor comes mostly from a few compounds. Peppermint is menthol and menthone. Menthol is what makes your mouth feel cool. Spearmint is mostly carvone, which reads sweeter and more like chewing gum.

The shake tastes softer than a peppermint candy because the vanilla soft serve and whipped cream round it off. Fat holds mint oils and lets them go slowly. Sugar takes the edge off the cooling.

Building a mint shake

Do not use the name. "Shamrock Shake" is a McDonald's trademark. Sell a "mint shake" and avoid anything that suggests a link.

Decide peppermint or spearmint. Peppermint reads cool and candy-like, and at high doses like toothpaste. Spearmint reads sweeter and more like gum. Blends are common.

Fat level changes the dose. Reduced-fat soft serve lets mint come through faster and sharper than premium ice cream at the same dose. Re-taste if you change the base. See dairy for why fat changes release.

Green is harder than it looks. Third-party copies of the Shamrock syrup's ingredient list show Yellow 5 and Blue 1. In the US, the usual route to a green from exempt colors is spirulina blue blended with a yellow such as turmeric or safflower. Sodium copper chlorophyllin is common elsewhere, but here it is only permitted in citrus-based dry beverage mixes. Spirulina is sensitive to heat and acid, the same problem natural blue raspberry products face, though a neutral dairy base is kinder to it.

Plan for a short window. A seasonal mint product has a few weeks to sell. Packaged versions need flavor, color and packaging locked well before that.

Mint and chocolate is the obvious extension. McDonald's itself has sold chocolate and coffee versions of the Shamrock flavor. For another coffee-and-dairy profile, see mocha.