It turns out, vegans shouldn't add a lemon to their drink [Photo: Getty]

It turns out, lemons aren’t strictly suitable for vegans and social media users are puzzled.

Cookbook author, Jack Monroe, sparked the debate when she noticed that the Pizza Express menu states that the brand’s Coca Cola is only plant-based “if served without lemon”.

Admittedly baffled by the claim, she shared a photograph of the warning on Twitter alongside the caption: “Erm what do Pizza Express do to their lemons to make them not suitable for vegans?! Just noticed this and can’t for the life of me fathom wtf.”

The tweet soon amassed over 1,000 likes with fellow users guessing why the fruit might not be plant-based.

Erm what do pizza express do to their LEMONS to make them not suitable for vegans?! Just noticed this and can't for the life of me fathom wtf pic.twitter.com/YF1LkjY80a — ☘️🇨🇾Jack Monroe (@BootstrapCook) September 18, 2019

READ MORE: 10 reasons to go vegan

The popular chain promptly replied to the tweet to end the debate, explaining that it’s down to the fact that the lemons used are waxed - therefore not vegan.

The wax on waxed lemons contain shellac which is derived from insects and therefore strictly not vegan. — PizzaExpress 🍕 (@PizzaExpress) September 18, 2019

Why aren’t waxed lemons vegan?

In order to preserve the fruit while in transit, lemons are often coated in shellac - which gives them that lovely shine - which is derived from resin secreted by the female lac bug found in India and Thailand.

After being processed and dissolved in alcohol, it becomes liquid shellac which is also commonly used to produce furniture varnish, confectionary and shellac nail polish.

READ MORE: As Primark launches vegan skincare range, shop 5 of the best cruelty-free beauty buys

Fruits may also be coated in beeswax in order to slow down moisture loss and prolong shelf life - again, problematic for vegans.

Blog Super Savvy Vegan contacted a number of supermarkets to find out which fruits were vegan-friendly and a list of suitable chains can be found over on the website.

Vegans were impressed with Pizza Express’ knowledge on the topic and praised the restaurant for its clarification.

I was super impressed by a waitress at Pizza Express for teaching us this fact that they cannot guarantee the lemons haven’t been treated with beeswax/shellac so want to be transparent at all times,” one wrote. “My vegan friend, who knows everything about vegan food, didn’t even know this.”

I was super impressed by a waitress at @PizzaExpress for teaching us this fact that they cannot guarantee the lemons haven’t been treated with beeswax/shellac so want to be transparent at all times. My vegan friend, who knows everything about vegan food, didn’t even know this🤷🏻‍♀️ — 𝙳𝚛 𝙿𝚞𝚗𝚊𝚖 𝙺𝚛𝚒𝚜𝚑𝚊𝚗 (@DrPunamKrishan) September 19, 2019

Another added, “I’d give Pizza Express props for being clued up on the matter.”

The wax on the lemons.. I’d give @PizzaExpress props for being clued up on the matter 👍 — Tempeh T Ⓥ 🌱 (@83426life) September 18, 2019

If you’re ever unsure when shopping for fruit, it’s best to stick to unwaxed fruit.

Watch the latest videos from Yahoo Style UK: