There are some recipes, that no matter how hard we try to replicate, we just can't seem to get the flavour right. Whether they're ancient recipes passed down by monks or popular brands that keep their formulas in locked vaults, some people would pay millions to get their hands on them. We take a look at products with top-secret recipes only known by select few.

Coca-Cola was invented by Atlanta pharmacist John Pemberton in 1886 and its secret recipe was purchased by Asa Griggs Candler for £1,810 ($2,500) some time between 1888-1891. Candler knew the recipe was a winning formula, so it was easily turned it into a successful company. Today, Coca-Cola is the most popular soft drink the world and its secret recipe is written on a piece of paper, which is not just kept under lock and key, but in a secure vault in Atlanta in the US. 

While reports vary, the most famous account says this popular hot sauce was first created by Ms Thanom Chakkapak in the small town of Si Racha in Thailand, however, it was Vietnamese refugee David Tran who began bottling it under a brand name in the US and made it famous. David made bottles of hot sauce from his home and eventually founded Huy Fong Foods. Although the ingredients of sriracha are not a secret, the sauce is made using machinery specially modified by David so it's near impossible to recreate the flavour of his sriracha.

One of America’s best-loved baked bean varieties is Bush's, which has been canning foods since 1904. Bush's hit the jackpot in the early 1970s when the baked beans, based on a secret family recipe, hit the shelves. All we know is that it contains beans, brown sugar and double-cured bacon, but that’s about it. The complex blend of spices and flavourings remain a secret that the Bush company is unwilling to spill. The Bush Visitor Center in Chestnut Hill, Tennessee houses the guarded display of the Bush's Secret Family Recipe book.

Rumour has it, Dr Pepper has gone one step further and keeps its secret recipe split in half in two security deposit boxes at two different banks. It was invented by pharmacist Charles Alderton at Morrison’s Old Corner Drug Store in Texas in 1885. Alderton loved to experiment with syrups and the soda machine and eventually came up with the perfect formula. In 2009, an old ledger from Morrison's was discovered and in it was a written recipe for Dr Peppers Pepsin Bitters, containing mandrake root, wahoo bark and bitter orange peel, but it hasn't been confirmed whether it's true.

Worcestershire sauce is a great addition to cheese on toast, stews and meat marinades, to name just a few. The ingredients on the back of the bottle list spices, but the exact mix remains a secret. The sauce was invented by Worcester chemists, John Wheeley Lea and William Henry Perrins in the 1830s when nobleman Lord Sandys wanted them to recreate the flavours he tried on his travels around India. 

You may be able to find Portugal’s celebrated custard tarts in almost every bakery in the country, but the original can of course be found at the Pastéis de Belém pastry shop near the Heironymite Monastery (Mosteiro des Jerónimos). The tarts were invented by monks at the monastery and the shop started making them to their original recipe back in 1837. This secret recipe has been passed down through the generations and today they are still made by hand using the traditional methods. 

The city of Toruń in Poland has been the true capital of gingerbread since the 13th century. Every baker in the city had its own secret recipe for the spiced biscuits. In 1556, however, a new rule passed, allowing Toruń bakers to share their recipes with those from Nuremberg in Germany and vice versa. Since then, both cities have become celebrated for their gingerbread, perfecting their recipes over time. Today, bakers in Toruń still bake their gingerbread as per an original but secret recipe that includes a very delicate spicing, using ginger, cloves, cinnamon, cardamom and more.

Often described as Scotland's other national drink – Irn-Bru has been around since 1901 and is still made to the original secret recipe, which contains 32 different flavours. The ingredients on the bottle only list three different flavours – caffeine, quinine and ammonium ferric citrate – but the others remain a mystery. The top-secret recipe has been passed down through generations and today there are only two people in the world who know exactly how to make it, both from the founding Barr family.

Yemas de Santa Teresa are a typical sweet from the Spanish city of Ávila. Yellow in colour, their main ingredient is egg yolks. Some say they were invented by local nuns, while others believe it was Don Isabelo Sánchez, owner of La Flor de Castilla bakery, who made them first in 1860. Today, the bakery still exists, and its egg-based recipe has been passed down in secret through generations.

Once a luxury only for the rich due to fresh milk in it spoiling fast, milk chocolate wasn't widely available until Milton Hershey found a way to mass produce it. He spent three years experimenting and perfecting his milk chocolate production before he launched the company's signature bar in 1900. The exact process is still a closely guarded secret, but it is thought that the milk undergoes lipolysis, whereby fats are broken down by hydrolysis to release fatty acids, which prevents the milk from further fermentation.

Aachener Printen are soft spiced German cookies, somewhat similar to gingerbread. They are actually thought to have originated in Dinant, Belgium and were brought to Aachen by craftsmen during the 15th century. Most people believe they are flavoured with cinnamon, cardamom, aniseed, cloves and coriander, however, the exact recipe and quantities are top secret, and each bakery in the city has its own unique method. Today, Aachener Printen is a product of protected designation of origin (PDO), meaning the real deal is only made in Aachen.

Slightly different from Bakewell tarts, Bakewell puddings are the original dessert that hail from Bakewell in the UK’s Peak District. There’s no icing or glacé cherries here, just pure almond gooeyness. It's unclear exactly how the recipe originated and who came up with this ingenious dessert as the accounts vary greatly. Today, the core ingredients for a Bakewell pudding aren't a secret, however, some ingredients still remain a mystery. The most popular purveyor of Bakewell puddings, The Original Bakewell Pudding Shop in Bakewell, still use the age-old recipe. 

When Universal Parks & Resorts opened the Wizarding World of Harry Potter, a recipe for Butterbeer had to be invented. It took chef Steve Jayson three years to come up with the final concoction, which is a closely guarded secret now. As JK Rowling doesn’t actually describe the flavour in the famous books, it was a difficult task. We don’t know much about what the drink contains, but what we do know is that it's dairy-free and tastes like cream soda and caramel.

It is said that Krispy Kreme founder Vernon Rudolph bought the special doughnut recipe from a New Orleans French chef in preparation for opening his first store in 1937 in Winston-Salem, North Carolina. Food historians believe that the original recipe contained fluffed egg whites, mashed potatoes, sugar, shortening and skimmed milk. The company says its signature Original Glazed Doughnut recipe hasn't changed since 1945 but it's not been revealed in full.

The celebrated Italian aperitif is the main ingredient for some of the world’s most-loved cocktails, including the negroni. It was invented by Gaspare Campari in 1860 and its original recipe remains completely unchanged since. All that is known is that it's a concoction made from bitter herbs, aromatic plants and fruit, but what or how many remain a mystery. Many have guessed there are anywhere between 20 and 80 ingredients in Campari, but alcohol and water are the only two known ingredients to this day.

Kendal Mint Cake is not actually a cake at all, but a sweet peppermint energy bar. Joseph Wiper invented it by accident in 1869 in the town of Kendal in the north of England. In 1912, Joseph’s great nephew took over the business and marketed it as an energy bar for mountaineers and climbers. Since then, both Sir Ernest Shackleton and Sir Edmund Hillary took bars of it on their expeditions. Romney's bought the business in 1987 and says it still makes it per the original secret recipe.

The chocolate giant’s secret formula is clearly a winning recipe as Cadbury is quite possibly the UK's most-loved chocolate. The Dairy Milk bar was invented in 1905 by George Cadbury Jnr, 76 years after his father John Cadbury started the business. His aim was to create a milk chocolate bar with more milk than any other on the market. We know there's milk, sugar, cocoa butter and cocoa mass among the ingredients, however, the quantities or how the chocolate is made remain a secret.

In 1605 the monks of the Chartreuse monastery received a gift from Francois Hannibal d’ Estrées – a manuscript for elixir of long life written by a 16th century alchemist. It wasn’t until 1737, however, that it was deciphered by La Grande Chartreuse monastery's apothecary, who then wrote a recipe and started selling the small bottles of it in Grenoble and nearby villages. Said to contain 130 different herbs, plants and flowers, today Chartreuse is still made to the original recipe and its herbal mixture is only known by two monks at Grande Chartreuse who prepare it.

Piononos are the most famous sweet pastry from the Spanish region of Granada and, more precisely, the small town of Santa Fe. These bite-sized cakes are based on an ancient secret recipe. It is said that three sisters who owned La Blanquita bakery in Santa Fe rediscovered this recipe in the 19th century. They decided to name it after Pope Pius IX's name in Spanish, Pio Nono, because the pastry resembled papal clothing.

These food brands owned by celebrities might surprise you

Entrepreneur Alessandro Martini and master herbalist Luigi Rossi created the secret recipe for the world’s most famous red vermouth in 1863, when they took over the National Wine & Spirit’s Distillery near Turin in Italy. Today, over 150 years later, their undisclosed blend of herbs and botanicals remains just as popular. The only ingredients that the company lists on its website are Italian herbs, including sage, savoury and dittany, and bittersweet exotic woods, but the exact recipe remains a secret.

Whether you love it or hate it, the secret of the salty breakfast spread has been baffling us for years. We know of course that one of its main ingredients is yeast extract, but the exact spices and flavours remain a top trade secret. Marmite was invented in the 19th century by German scientist Justus von Liebig, who discovered that the by-product of brewing could in fact be eaten. The Marmite Food Company took this idea and began manufacturing the spread from 1902 in Burton-on-Trent, England.

We all know KFC's original fried chicken is made with a secret blend of 11 herbs and spices, which was invented by its founder Colonel Sanders. Sanders began serving chicken from his café in Kentucky and opened his first franchise in Utah in 1952. In 2017, a journalist from the Chicago Tribune claimed he had discovered the secret when Sanders’ nephew showed him a scrapbook with the recipe inside. KFC denied that this is the true recipe and claimed that no one's ever been right recreating it.

Discover fast food favourites from the year you were born

America's favourite condiment was created by Henry J Heinz in 1876 with just five ingredients. Initially called catsup, it rapidly grew in popularity and was shipped all over the world as early as 1907. In 1936, Heinz even began his own tomato breeding programme to grow the best for his ketchup sauce. Today, the ingredients on the bottle include tomatoes, vinegar, sugar and salt, as well as spice and herb extracts, which surely are the secret to its addictive taste.

Now take a look at fast food giants that have revealed their secret recipes