The molecular reason avocado toast tastes so good

All about the hexanal: the signature avocado toast at Bill's in Darlinghurst, Sydney.
All about the hexanal: the signature avocado toast at Bill's in Darlinghurst, Sydney. Photo: Edwina Pickles

A group of food scientists in Belgium have discovered why avocado tastes so good on sourdough toast. It's not just the crunch of the bread or the creaminess of the avocado. It all comes down to a molecule called hexanal. 

This compound of carbon, hydrogen and oxygen is found in many plants, but it's also produced during sourdough fermentation. When avocado comes in contact with sourdough, the naturally occurring hexanal in both ingredients pairs up and makes the other aromas blend perfectly together. 

This and other culinary matches, such as caviar and white chocolate, and oysters and kiwifruit, are explored in The Art and Science of Food Pairings, published this week by Hachette. 

Ham-and-pineapple pizza lovers have molecular science to support them.
Ham-and-pineapple pizza lovers have molecular science to support them. Photo: Lauri Patterson

Belgian lab Foodpairings is behind the book, which contains more than 10,000 ways unlikely combinations, such as strawberries and parmesan, can become delicious tablemates. 

"Their ideas are liberating," says Sydney patissier Johann Vanier, who specialises in beautifully crafted pavlovas at Brookvale's La Pav'. As a senior pastry chef working in French Michelin-starred restaurants, he would often use the Foodpairings website for inspiration.

"The combinations are not necessarily from tradition, but are truly wonderful," he says. This summer, Vanier is flavouring his pavlovas with strawberries and Champagne; raspberry, rose and lychee; and pineapple, fennel and aniseed. 

The new book by Peter Coucquyt, Bernard Lahousse and Johan Langenbick.
The new book by Peter Coucquyt, Bernard Lahousse and Johan Langenbick. Photo: Hachette

Foodpairings was founded by three scientists in 2009 and uses gas chromatography-mass spectrometry to analyse the aromatic components of foods. Algorithms compare the results with other foods to find taste pairings a chef might take years to discover in the kitchen. 

Using this method, the team discovered sweet potato and mango had enough aromatic compounds in common to sit tastily in a dish together. As do vanilla and white asparagus; broccoli and dark chocolate, and cheese and pineapple – a combination appreciated by Hawaiian pizza-lovers every day. 

Speaking from Belgium, Foodpairings co-founder and co-author of the book, Peter Coucquyt, said "due to the pandemic trends have switched, mainly to health and building immune systems".

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He refers to the unlikely pairings of chocolate brownie with fermented white miso and roasted beetroot with sesame seed. Coucquyt suggests we will be washing these down with kefirs flavoured with apple, peppermint and lemon geranium.

"Fermented foods are trending," he says.

The Foodpairings scientists have also collaborated with thousands of chefs, bartenders and food businesses worldwide, including Melbourne's Darren Purchese of Burch & Purchese Sweet Studio, South Yarra. 

"Those guys are awesome," says the pastry chef, whose coconut, passionfruit, ginger and mint tube cake was co-created by Foodpairings when Burch & Purchese opened in 2011. 

"We also worked on a collaboration in China where we made a dessert with apple, eucalyptus, and cucumber," says Purchese. "It sounds odd, but they made it work." 

Five left-field food pairings 

White chocolate and caviar

Salt inhibits the tongue's ability to detect bitterness, a taste that defines chocolate. Understanding this, British chef Heston Blumenthal experimented with salty ingredients and chocolate until he settled on a dish that became part of his repertoire: cold and salty caviar on top of a creamy white chocolate disc. It has been described by gourmands as "stunning".

Chicken and liquorice

Liquorice and chook have aromas in common, The Art and Science of Food Pairings suggests trying a variation on chicken and apricot tagine made with hazelnuts rather than almonds, and liquorice for depth of flavour.

Turkey and creme de cacao

Chocolate is used in traditional Mexican mole sauce served with turkey. The logic goes that a dash of creme de cacao liqueur, with its intense chocolate aroma, would work well in a sauce for the bird, too.

Black truffle and French fries

The ultimate high-low pairing. According to the food scientists, frying fish in batter creates caramelic and roasted notes that pair perfectly with chips. Black truffle not only shares fruity notes with cod, it can also take fries to another level, especially when the golden rods are dipped in Belgian-style in truffle mayonnaise.

Cauliflower and strawberry

Orange aroma compounds make cauliflower possible to combine with a variety of citrus and other fruits, including strawberries. Recipes exist for cauliflower-strawberry smoothies, but a salad pairing the ingredients is potentially tastier.