When many people reach for a glass of wine, it’s quite often after a particularly stressful day, or to unwind with friends - but rarely do I think about what is inside it.

For some wine drinkers, experts and buyers that is the main premise of the wine they promote and sell. They are devoted to producing only natural wine, something different to what is in most supermarkets and restaurants.

The reason? Many mainstream wines contain additives and sulphites, and sometimes animal derivatives are used in the fining process of mainstream wine.

The animal rights campaign group Peta even warns on its website of the animal-derived fining agents which can be used including “blood and bone marrow, milk protein, chitin (fibre from crustacean shells), egg white derivative, fish oil, gelatin and isinglass (gelatin from fish bladder membranes)”. There is now a growing number of vegan wines, also available in many supermarkets, which do not use animal derivatives in their fining process.

Isabelle Legeron, the founder of the Raw Wine fair, says that natural wine is anything which is made “organically and with very little, if any, additives”.

"I was always into wine and I love nature and the environment,” she told The Independent. “I stumbled across this little world of natural wine that resonated with my values: wines which were really authentic and expressive and decided that it was only thing I wanted to drink or work with.”

She says the problem with non-natural wine is not dissimilar from the way food is farmed normally compared to organically. In wine-making, when conventional agriculture is used, this includes the use of synthetic pesticides and weed killers.

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John Lang, 47, and his partner Jane Honeymoon co-founded the Good Wine online shop in 2007. They did so in response to Ms Honeymoon’s severe, and potentially fatal, sulphite allergy – something commonly found in wine – which they found out about in 2005.

Sulphites are preservatives used in the production of some foods and drinks and work by releasing sulphur dioxide. EU food labelling rules mean that all food sold in the UK must show on the label if it contains sulphites at levels above 10mg per litre, they often show up as ‘e-numbers’ like ‘E220’. A quick scan of wines in major supermarkets and you will see the ‘contains sulphites’ warning label.

There is also conflicting arguments as to whether it is the additives in wine which cause hangovers, with Lang saying he has not had a hangover in 10 years.

Lang told The Independent a common misconception is that “wine is all the same” however, he claims most shop-bought wine actually contains a worrying number of additives and sulphites.

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He explained that his wine makers farm their land without any chemical pesticides or herbicides, and would usually have an eco-system in their vineyard of other plants, animals and insects which control the potential pests and diseases. When the grapes are picked, he says the producer hand-sorts the grapes to make sure only the good grapes were used. They would then be fermented with their natural yeast.

“As the grapes were fully ripe, the resultant wine has sufficient natural sugar and sufficient natural acidity to produce great wine,” he says. “They would then fine the wine to remove excess grape particles. The natural antioxidants present will preserve the wine so most producers would add just a tiny amount of sulphites to kill off any bacteria and eliminate any oxygen present. Literally adding 20 parts per million or less. Some add none at all.”

He says this compares to larger producers who often try to ferment all the grapes in one go, so when some of the grapes were not deemed good enough they would add extra sugar, ‘correctives’ and sulphites.

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Lang, who carefully vets and selects wines from vineyards in France, Italy and California, warns of wines which are bottled in the UK but produced abroad, saying the ones produced in the UK will usually contain more sulphites.

Aside from the additives and sulphites, sometimes animal derivatives are used in the fining process of mainstream wine.

Legeron says sometimes eggs and gelatin are used in the clarification process used in wine making, as some producers do it instead of wait for the natural clarification process.

So as the organic food market has grown, has the natural wine movement? Legeron says natural wine producers only make up a “tiny proportion of the wine industry” and likens it to finding organic bread or meet or craft beer.

Perhaps, most importantly for some, how does natural wine taste?