NORMALLY I would be laughed out of town if I tried to pass off a drinking bout as educational, writes Louise Vennells. But hold your sniggers and bear with me – I've been looking round the Plymouth Gin factory purely in the interests of investigative journalism. Honest.

I even got to make my own gin. Never has science been so engaging as when I gazed enthralled at the network of glass tubes that was yielding my very own batch of the spirit, drop by tantalising drop.

I also learned how Plymouth's gin production has survived the centuries and owes its special flavour to a unique combination of Devon's pure water and carefully-selected herbs and spices.

My expert guide was Sean Harrison, the company's master distiller. And my visit was accompanied by several shots of the wonderful, cheek-warming drink itself, available in abundance to anyone with the foresight to have left their car at home.

The highlight of my visit to the 600-year-old factory on the water's edge in Plymouth was my chance to distil my own mini bottle of the spirit. To do this, I carefully selected the ingredients to drop into a flask of neat alcohol.

First in, of course, were the obligatory dried juniper berries, which are essential if the brew is to be classified as gin. I then opted for a pinch of dried sweet orange and lemon peel, a touch of angelica root, a sprinkle of powdered orris and a cardamom pod from the pots of ingredients available. But I gave liquorice and nutmeg the go-by – they have no place in this most hallowed spirit, in my view.

Sean carefully connected the flask of bobbing spices to the heater, which in turn was connected to a structure of glass pipes and cooling chambers. As I practically hopped around with excitement, the alcohol began to bubble away at around 75C, releasing the delicious aroma of essential oils into the air.

Slowly, the steam began to condense, working its way around the transparent tunnels to collect in droplets, into a separate bottle, which is now my most cherished possession. Well, for the short time until it is drained empty, that is.

Sean is keen to nurture appreciation of the tipple and to abolish what he calls the "Pat Butcher" G&T, served in a wine glass, with one ice cube and a slice of lemon. "Gin should be enjoyed long and cold," he said. "If I'm drinking it with tonic, I use a natural one that's saccharine-free. It makes all the difference to the taste."

His attention to detail is essential – one handful of juniper berries that has more oil than another can totally alter gin's final flavour. Sean's pride in his product is natural, considering that Plymouth Gin is thought to have inspired the world-famous martini (a cocktail of gin mixed with vermouth and an all-important olive).

"People need to give gin a bit more respect," says Sean. "It's a lot trickier to make than people realise. We're flavouring the alcohol – and if you get it wrong, you get it really wrong."

Each ingredient is carefully selected from scores of different samples, but no two batches are ever the same. To provide consistency, four different batches are mixed together before the end product is bottled.

When gin first tickled British tastebuds, anyone who had the means could create a distillery in their own back garden. The idea of nipping out to siphon off a double from your very own still might sound heavenly – but in the harsh realities of 250 years ago, it was anything but.

The spirit was blighted by a lack of knowledge on the right boiling temperatures, meaning dangerous methanol was not always properly separated off, and damaging sulphuric acid was sometimes added. The term "mother's ruin" was coined to encapsulate the resulting health effects. Among its many dangers, it was believed (probably quite rightly) to induce miscarriages in women.

Fast forward a couple of centuries and Plymouth Gin is a different product altogether, even though the building that houses the factory was already standing in those dark days.

These days it has a stylish cocktail bar, well worth a visit, which sells a vast choice of gin mixes, including a variety of takes on the martini. From Easter anyone with £40 to spare can spend a fascinating two-and-a-half hours in Sean's company, as he takes visitors on a trip round the factory to explain the journey of gin.

During my visit, I learned that the drink originated in Holland, where juniper was added to alcohol as it was thought to have medicinal qualities. It also tasted rather good and production was thriving by the mid-1500s, soon spreading through Europe. During the 17th century, "jenever", as it was known, was nicknamed "Dutch Courage" by troops fighting in the European wars. The drink was then brought to Plymouth by seafarers returning from overseas.

When the Dutchman William of Orange landed in Brixham in 1688, Plymouth was the first town in England to support him. His retainers stayed in the area and set up the base of what is now Plymouth Gin.

But the real forefather of Plymouth Gin is widely acknowledged as Thomas Coates, who joined an existing distilling business in the city in 1793 and eventually took it over.

The company prospered and by the 1920s Plymouth was one of the best known gins in the world, featuring heavily in the Savoy's oh-so-smart cocktail menu. Sadly the rationing of the Second World War then took its toll, and instead of stopping production because of a lack of grain, the owners unwisely introduced inferior ingredients. Demand, unsurprisingly, dwindled.

But today Plymouth Gin is on the ascendant once more. It's now owned by French company Pernod Ricard, who, Sean says, understand the importance of the special Devon water the factory uses. It's naturally filtered through Dartmoor peat. And the secret blend of angelica root, cardamom, coriander seed, lemon and orange peel and orris root needed for Plymouth Gin is at its very best these days.

I had the hardship of comparing Plymouth Gin against four other leading brands during my tour and I can confirm it is indeed a real winner. To taste gin properly, you dilute it with water, sniff heavily and then taste, to explore the remarkably different notes and finishes. I was able to identify Gordon's from many a disappointing pub gin and tonic and Hendricks, because of its strong floral aroma. Plymouth Gin, by contrast, has a fresh juniper taste and smooth, citrus flavours.

As for my own batch – it was, says Sean, "dry and light with notes of sweet citrus". In both our opinions it was also "very drinkable indeed". So here's to many more centuries of gin making in the Westcountry – and why not try it out for yourself in some of these classic Plymouth Gin cocktail recipes?

The Master Distiller's Private Tour of Plymouth Gin Distillery lasts 2½ hours and costs £40. Book in advance on 01752 665292. Other tours are available.