Liquid assets: the surprising role of minerals in wine filtration

In 2020, it was estimated that between 253.9 million and 262.2 million hectoliters of wine were produced across the globe – enough to fill more than 10,000 Olympic-sized swimming pools.

The majority of this wine would have gone through some form of filtration – the separating of solid particles from liquid – before being bottled, sold and, ultimately, consumed. 

A common and the longest-serving method for filtering wine, champagne and other sparkling wines is the use of mineral filter aids – solid materials that improve filtering efficiency. 

Filter aids prevent blockage by forming a porous filter cake (particles retained on the filter) around the filter, allowing for the uninterrupted flow of liquid to pass through and trapping large solids. 

The filtration process for red and white wine

Filtration in wine production is largely carried out to remove undesired solid components, such as protein and yeast, and for aesthetic reasons and to improve shelf-life. It can take place multiple times and at different stages of the production process, depending on the type of wine that is being produced. 

The first stage commonly occurs during the crushing of the grapes – to remove the grape seeds and, if producing white wine, the skins. For red wine, the skin of the grape is kept to give the wine its colour. 

The resulting juice is then injected with yeast for the fermentation process when the yeast converts the juice sugars into alcohol. 

Two or three weeks later, the next filtration phase takes place, to remove the yeast and any precipitated materials from the wine. Again, the liquid doesn’t need to be perfectly clear, as it is transferred into maturation tanks or barrels for further ageing.

Some protein complexes are still too small to filter – but if they are left, over time they will form into a mass, either making the wine cloudy or becoming sediment at the bottom of the bottle.

Therefore, after filtration, the wine is usually transferred to a large tank, where a fining agent, bentonite, is added as a slurry in water. Over several days, the bentonite chemically bonds (adsorbs) the proteins and settles at the bottom of the tank. This "sludge" is removed and the "clarified" wine above is sent to a storage tank (or barrels) for ageing and/or further filtration before bottling.

The final filtration step – just before bottling – will be where wine producers look to get the best clarity possible. When producing red wine, however, this isn’t as much of a concern, so this final filtration may not be required.

As well as providing clarity and removing unwanted particles from wine, filtration can also serve a necessary purpose in ensuring wine is safe to drink for those with specific allergen needs. 

Fining agents – often containing potential allergenic food proteins – are sometimes added to wine for a number of reasons, including to modify the texture or flavor. While the fining process is designed to dispel all fining agents once their purpose has been served, the use of best practice filtration methods – like filter aids – is still encouraged in order to confirm that no residual agents can be detected.  

Porous diatomite and perlite make excellent filter aids 

Imerys has been selling filter aids to the wine industry since the 1930s. It currently sells two of the most commonly used filter aids in wine production: diatomite and perlite. The properties of these natural and widely available minerals make them ideal for removing a wide variety of suspended solids. 

Matt Jordan, Performance Minerals EMEA Technical Support Manager, says: “Both diatomite and perlite are inert, meaning they don’t negatively affect the quality of substances they come into contact with. They’re also widely permeable, making it easy for liquids to pass through. 

“Diatomite, in particular, is also very porous, with a structure comprising thousands of tiny holes that make it excellent for filtering liquids containing fine particles”.

With an efficient ability to trap solids, less juice is lost in spent filter cakes when using filter aids, leading to more juice being fermented. 

Filter aids also offer flexibility when it comes to the pore sizes in filtration, as a range of different grades allows producers to choose how tight they want their filters to be. 

“The reason people don’t drink red wine fresh is because the complexity of the wine comes from small molecules combining – something that happens during the ageing process,” explains Matt. 

“Producers filter to give their wine a certain character. By offering them the chance to filter liquid using varying pore sizes according to their needs, they can build complexity into their wines at their own rate.

Wineries making boutique wines are most likely to use filter aids for filtration as quality is their number one priority. 

“Wineries all over the world – from Bordeaux to California – are very passionate about their processes and they take great care in the production of wine,” says Matt. “They favour tradition, and this is shown in the products they produce”.  

Sustainable solutions to filtration

These days, most of Imerys’ filter aids are supplied locally to customers in France, Spain and Italy – the three largest producing countries of wine, accounting for 49% of production across the world, and 81% of EU wine production. 

This localized approach is helping to reduce the carbon footprint of Imerys’ products, in turn supporting sustainability in the wine production supply chain. 

“Sustainability is a topic of major interest in the drinks industry, and we’re working on ways in which we can help our customers to improve in this area,” says Matt. “We have a couple of ongoing projects to look at how we can reuse our filter aids and also extract minerals from used filter cakes for other purposes. 

“Wineries put a lot of care and passion into the winemaking process, so it’s important that they’re able to find ways to be more sustainable without compromising the quality of their products and their craft”.

Imerys’ expertise in mineral-based filtration is not restricted to wine. Elsewhere in the food and beverage sector, Imerys filter aids are also used by brewers. And to improve healthcare, diatomite is used to remove contaminants in water in the developing world; and high-purity filter aids (HPFA) are used for solid/liquid separation in biotechnology and pharmaceutical applications.