Image copyright Marks and Spencer

Percy Pigs are a bit of a delicacy to some.

The Marks & Spencer sweets are pretty celebrated - and thanks to a veggie version without gelatin being launched in 2011, everybody can try them.

But M&S has managed to anger some Percy Pigs fans by completely removing gelatin from their main product - something described by one angry person online as "an assault on normal food".

So with Percy Pig gelatin outrage making it on to the front page of a national paper, we thought it was time to ask (and answer) some questions...

Let's start with, what is gelatin?

Image copyright Getty Images Image caption This chef is soaking gelatin sheets in water, but what are they?

Boil the bones, skin and tendons of an animal - usually pigs or cows - dissolve them in boiling water, leave it to cool, and you'll end up with something that looks a bit jelly-like.

That's gelatin.

If you've not got any bones going spare you can buy it in the supermarket, usually in leaf or powdered form.

It's odourless, flavourless and clear.

Why's it in our food then?

It might not taste of anything, but gelatin in food does serve a purpose - usually it's used as a thickener or stabiliser in desserts and sweets.

But it can also be found in stuff like yogurt, sour cream and margarine, as well as lots of other foods.

If you're worried about consuming gelatin, you should always check the label.

Can you find it anywhere else?

Gelatin can also be found in some cosmetic products, as well as in the pharmaceutical industry to make hard and soft pill capsules, among other things.

What are the alternatives?

Image copyright Getty Images Image caption Desserts made using agar agar look pretty similar to ones that contain gelatin

Something called agar agar, which is made from red algae, is often referred to as vegan gelatin and is used in lots of desserts.

There's also something called carrageen, which is a variety of Irish seaweed that has natural gelling properties.

M&S says it has replaced gelatin in Percy Pigs with pea protein and starch.

Some people say that moving away from gelatin has caused the taste of Percy Pigs to change.

M&S says it's been working hard and has "perfected a 100% vegetarian Percy - something our customers have been asking us for".

In a statement it told Radio 1 Newsbeat that the recipe has been tested to make sure it's "as close to the original as possible", and that all the "really important things people love about Percy" are the same.

"The flavour is the same, he still has real fruit juice and never has artificial colours or flavours."

It's not the first time a recipe change has resulted in anger

People like what they like - something Mondelez International found out when it changed the recipe for Cadbury's Creme Eggs a few years ago.

"What have you done?" was the cry from social media - and the recipe change was blamed for a £6m slump in Creme Eggs sales that Easter.

If you're still a bit wound up about it, this article is probably for you.

Special K, Coca-Cola, McVitie's Digestives and HP Sauce have all had recipe change controversies of their own.

But the final say on this goes to fans of Irn Bru, whose reaction to AG Barr halving the sugar content of the beloved orange drink was the sign of ultimate fandom: to stockpile it.

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