“Are lemons fast or slow?”

This is the question posed by Professor Barry Smith, director of the Centre for the Study of the Senses, University of London, at the beginning of our discussion about citrus.

I consider it for a split second, then reply: “Fast.” Lemons are fast. Of course they are.

Barry nods; everybody says fast. “And that’s cross-cultural; that’s universal. We can put that question to the web, we can pass it all around the world, and people will say lemons are fast. Bananas? Slow. And that seems intuitively right, but we don’t know why.”

It does seem intuitively right—lemons are fast. They’re immediately stimulating and evocative. If you even think of the word “lemon,” your mouth will start to water involuntarily. Lemons demand a response—and a quick one.

“I think that has to do with the speed of reaction to the taste of acid,” Barry explains. "Your sour receptors act very quickly. As soon as you get some contact with a fruit that’s acidic, they’ll fire—boom! Whereas sweetness has a slow onset, a banana has almost no sourness, but it has a slow buildup of sweetness, and then it lingers. That makes it natural to think of bananas as slow, and citrus as fast—zingy, enlivening, uplifting, energising.”

When you break open the skin of a tangerine, squeeze a wedge of lime over a bowl of noodles, or slice open a grapefruit, a fine mist of oils and juice escapes from the fruit, wafting up to your nostrils and coating your fingertips with a persistent perfume. There is such promise in that spray. It sends a signal to your brain to prepare for refreshment, for a jolt of vitamin C, for a flavour that can transport you to California, Koh Samui, or Christmas at your nan’s. Citrus aromas can induce feelings of both nostalgia and excitement, often simultaneously.

Drinks producers are constantly trying to capture that distinct citrus mist. Few have been as successful as Square Root, Hackney’s pioneering and award-winning soda makers. For founders Robyn Simms and Ed Taylor, lemons are fast in a different way—their ‘fruit-to-bottle’ process takes about 36 hours, a brisk pace that must be maintained to ensure minimal loss of flavour and aroma. When they first started out, Robyn explains, they were trying to make drinks that tasted as fresh as possible. But as they’ve grown, and have gained access to higher-quality ingredients while facing increasing competition, Robyn says they’ve shifted to try and make their product “the best.”

But after chatting to Robyn and Ed for a while, I got the impression that “fresh” and “the best” are often the same thing. I couldn’t stop thinking of the old culinary cliché: “fresh is best.” (Ed is even more of a hardliner: “Fresh or nothing,” he says.) That’s true of most fruit, but is particularly important for citrus, because of how quickly their volatile aromas dissipate and degrade over time. But of course, even the freshest of fruit is useless if you don’t process it properly.

Ed rails against products whose labels boast misleading and ultimately meaningless claims about provenance, like “made with Sicilian lemon juice.” The juice may be from Sicilian lemons, but then, as Ed explains, it’s “pasteurised and put into a tub. The tub can be kept ambient for any number of months, then it’ll be re-pasteurised after the first time it’s blended, and then it’ll go to another supplier that will potentially make that into a syrup, which will get re-pasteurised again. Then it’ll go into the bottle, and it’ll get re-pasteurised again, so that product could have been pasteurised four times. And you lose something every single time.”

All of this sounds needlessly complex and quite obviously detrimental to the flavour of the finished product, especially when compared to Square Root’s method, which is more labour-intensive, but more direct—it’s not that different from how you might make fresh soda at home, just on a much larger scale and with much cooler kit. The fruit is washed, then juiced; in the case of citrus, the rinds are poached in a sugar syrup to infuse their oils. The juice and syrup are then blended, carbonated, and bottled. Finally, the bottles are pasteurised at a low temperature. That’s it.

We crack open a few bottles of raspberry lemonade bottled the day before. It is amazingly good, so full of ripe raspberry flavour I almost expect to find seeds stuck in my teeth after drinking it. Later on, I sample a bottle of their Seville mandarin soda, made specifically to capture the oils from the peels of Seville oranges and Sicilian mandarins. It has a gorgeous floral-herbaceous aroma, and also a totally unexpected “tingly bang” sensation (Ed’s words) on the lips, something I’ve only ever gotten from fresh citrus peels before—never from a drink. It is an astonishing whole-fruit experience.

“We deconstruct citrus pretty well here,” says Ed, modestly.

Over the course of our chat, a number of our other favourite citrus fruits come up—yuzu, Meyer lemons, finger limes, tangelos, mandoras, mandelos, dekopon, calamansi, limequats, Tarocco blood oranges, and one in particular we all agree is seriously underrated and under-utilised: bergamot.

“After rinding them, your hand is just dripping with oil,” Robyn says, and she tells me a story about how their quest for the best fruit led them to an Italian farmer who “was very attached to his bergamots” and nearly rejected their order after exclaiming “No! My bergamots are perfume-quality only!” Luckily, in the end he was convinced to supply them after learning about their process and the high calibre of their sodas. But it’s that commitment to sourcing the best possible produce that sets Square Root apart.

““Your sour receptors act very quickly. As soon as you get some contact with a fruit that’s acidic, they’ll fire—boom!””

— Barry Smith

Of course, if sourcing great citrus in the UK is a challenge, imagine what it’s like to actually grow it here. There is just one dedicated citrus nursery in Britain—the Citrus Centre in West Sussex, founded by Chris and Amanda Dennis 25 years ago. They were initially drawn to raising citrus because they relished the challenge. It all started with “one small calamansi tree,” Chris explains. “We picked one up at the garden centre, took it home, and then had real trouble trying to keep it alive.”

They eventually realised that citrus trees need to dry out thoroughly in between waterings, something they discovered by accident after leaving a lime tree in a particularly sunny and well-drained corner of the garden—that little tree ultimately produced enough blossoms for Amanda to wear in her hair and include in her bouquet at their wedding. That initial, joyous success set them on course to grow all sorts of new citrus varieties, now contained in a series of temperature-controlled greenhouses.

In early May when I visit, these greenhouses are a paradise in Pulborough, a dense jungle of glossy green leaves with glimmers of yellow and orange fruit shining through the foliage like rays of sunlight. But what hits me first is the smell—many of the plants are inflorescent, and the aroma is like hot jasmine tea.

Chris and Amanda agree that the smell of the fresh citrus fruits and flowers is exceptionally invigorating, but when I ask them whether lemons are fast or slow, they’re the first people to suggest that they might actually be slow. “They feel fast, but they’re not a quick fruit to grow,” says Chris. “They take time, in our climate; it’s not like a lettuce plant, where you plant a seed and 20 days later you’ve got lettuce.” Amanda concurs, explaining how citrus trees take years to blossom, and then take many months—sometimes more than a year—to produce fully ripe fruit.

I pose another question: “Is citrus summery or wintery?” I myself am of two minds about this. While I mostly associate citrus with sipping Arnold Palmers or margaritas on sunny summer days, most of my favourite citrus, like yuzu, grapefruit, and dekopon, actually fruit in the winter. Chris says it depends on the fruit—like many British people, he associates oranges with winter, and particularly Christmas, due to the tradition of stuffing satsumas into stockings. But others, like lemons and limes, are more summery—“because that’s what you need for your gin and tonics!”

I am reminded of a story Professor Smith told me about the Greek goddess Persephone. As punishment for eating three forbidden pomegranate seeds while in the captivity of Hades, Demeter decided that Persephone would have to spend three months of the year in the underworld, during which time the Earth would grow cold and dark, and crops would not grow. This is why we have winter, according to the legend. English aristocrats in the Stuart period took to raising exotic plants in their greenhouses, and made a particular point of growing pomegranates in the winter months as a direct rebuke to Persephone’s punishment, commanding nature and creating their own summer in defiance of the gods.

I can’t help but feel that growing citrus, eating citrus, and bottling citrus sodas in England are similar acts of rebellion against the heavens. Bring on the grey skies, cold winds and rain—we can make our own sunshine, in the form of these most improbable, most enlivening, most wonderful fruits.