New allergy warnings are appearing on wine labels. Many drinkers will be astonished to be told their wine contains milk, eggs or fish. But it ain’t necessarily so.

These substances can be used during the processing of wine but none should appear in the finished product. The burden, though, is on the winery to prove there isn’t even the minutest trace of the substance. Since that is difficult, if not impossible, and needs expensive testing, most wineries that use them will just add the warning.

But what on earth are wineries doing with eggs, milk and fish in the first place?

It’s an age-old practise called fining. After the tempestuous fermentation and crushing of grapes there is a lot of sediment in the wine. Most will fall to the bottom of the tank to be left behind as wine is pumped off (a process known as racking) but there will still be minute grape particles left.

Consumers understandably do not like cloudy wine, we like it to be bright crystal-clear in our glass. Hundreds of years ago winemakers found that they could clear – or fine – the wine by adding a substance that attracted particles to it.

The white of eggs, beaten and added to a barrel, will slowly sink down pulling all the solids to it. That’s why omelettes and egg-yolk rich cakes are the traditional food of grape-pickers at harvest time. What the old-timers didn’t know, and science has since shown us, is that an electrostatic charge is created so the ball of egg whites attract the microscopic dusts to it. Wine can then be taken out leaving the egg with all the unwanted dirt.

Other materials that work in the same way are isinglass, which is made from the swim bladders of sturgeon fish and casein, which is made from milk. Hence wines not using these ingredients may be labelled as suitable for vegetarians or vegans.

Mega wineries producing hundreds of thousands of bottle won’t be breaking eggs. They pump wine through very fine filters, but many artisan winemakers say that filtration strips out elements that provide flavour. So you tend to find the smaller wineries using traditional fining methods and these will be the ones carrying allergen warnings.

Should you avoid wines with these allergen warnings? I’m not your doctor, but remember nothing has changed apart from the label.

None of the fining agents will in the wine and to my way of thinking I’d rather a flavoursome wine made by traditional fining methods.

What do you think? Tell us on our forum.

Peter F May is the author of Marilyn Merlot and the Naked Grape: Odd Wines from Around the World which features more than 100 wine labels and the stories behind them, and PINOTAGE: Behind the Legends of South Africa’s Own Wine which tells the story behind the Pinotage wine and grape, also available for the Kindle.

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