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When wine has a thirst for research. © FOTOLIA, Fotolia

When wine has a thirst for research

New winemaking practices

At the end of fermentation, the wine is cloudy, gassy and unstable.  It is then run off into stainless steel vats or oak barrels reserved for ageing, during which it becomes refined and clarified.  INRA researchers have developed a certain number of innovations and processes that can help winemakers to improve the quality of their wines.  The objectives are optimum microbiological stability, ideal clarity and rapid and efficient bottling.  Studies are ongoing at all levels of winemaking, and include processing the waste it generates, with notably the development by INRA of a biological pollution control process that uses activated sludge.

Updated on 11/18/2013
Published on 11/18/2013

Through the membrane

Calcium tartrate. Deposit in wine.. © INRA, MEYER J.P.
Calcium tartrate. Deposit in wine. © INRA, MEYER J.P.
For the past 20 years, researchers have constantly been imagining new membrane-based processes.  These include electromembrane systems that can extract ions from wine to ensure its sustainable stability once it has been bottled.  Other processes, using dense or porous membranes, enable a reduction in the alcohol content of wines.  These membranes of different types and with selective permeability, can all improve wine quality.

Eliminating tartrate deposits
In bottles of wine, tartaric acid, potassium and calcium may combine naturally to form tartrate salts whose presence is not appreciated by consumers.  INRA researchers have developed a technique that can prevent these deposits by eliminating excess potassium and tartaric acid from wine before it is bottled: tartrate stabilisation by membrane electrodialysis.  This involves the simultaneous extraction of anions (negative ions) and cations (positive ions), resulting from the alternation of anionic and cationic membranes. This technique has been authorised since January 2002, including for PDO wines.  This highly qualitative process is now being developed in all winemaking countries throughout the world because of its reliability.  This membrane technology also means it is no longer necessary to add various stabilising compounds to the wine.

Acidifying/de-acidifying wine
For numerous reasons (climate change, viticultural practices, etc.), the pH of wines has tended to rise in recent years; in other words, wine has become less acid.  But acidity has a crucial effect on both bacteria and the organoleptic properties of a wine.  To lower the pH of wine, INRA researchers have developed a electromembrane process to acidify wine that is both controlled and reliable.  Approved since January 2011, this treatment is now available at an industrial scale, including via service providers operating mobile units.  By contrast, in order to raise the pH, it is possible to de-acidify wine using electromembrane processes that have been authorised for winemaking since February 2013 and involve the extraction of excess organic acids.  This new research area is of particular interest to Northern winegrowing countries.

Optimum filtration!
Surface crust formed during the tangential microfiltration of a red wine. © INRA, COT Didier, VERNHET Aude
Surface crust formed during the tangential microfiltration of a red wine © INRA, COT Didier, VERNHET Aude
For commercial purposes, it is necessary to achieve the highest possible clarity and microbiological stability of a wine, and this is the objective of tangential microfiltration.  Having been the subject of basic research by INRA, clarification by tangential filtration allows the liquid to circulate along a special membrane at a relatively  high rate (a few metres per second) and then pass it through the membrane under the action of pressure.  These processes are now being used increasingly by producers.  
At present, the most sophisticated installations combine these different technologies: the on-line treatment of raw wine to enable rapid bottling that also ensures the clarity and microbiological and tartrate stability of wines.  A major advance for producer-based bottling plants, these continuous, on-line and automated treatments can guarantee the quality and traceability of wines.  Traditionally, winemaking practices involved the use of technological auxiliaries, inputs that were subsequently eliminated from the wine (e.g. fining).  At present, INRA is devoting many of its research projects to the development of wines that contain the fewest possible additives, thus avoiding recourse to stabilisers or ion exchange resins.

Pulsed electric fields

This technology under study at INRA enables satisfactory microbiological stabilisation by varying electrical intensities and treatment times.  This work has shown that the process is efficient in increasing the extractability of phenolic compounds from the skin (tannins and anthocyanins).  The quality of the vines produced using this low-energy technique complies with that obtained using traditional winemaking methods.

Clouds in white wines

Thermal emission from the bottom of a barrel, visualised using an infrared camera.. © INRA, HANOCQ  Jean-François
Thermal emission from the bottom of a barrel, visualised using an infrared camera. © INRA, HANOCQ Jean-François
What happens at ambient temperature in a white wine? During the transport or storage of these wines, a "protein breakdown" (visual disturbance) may occur and constitutes a defect in the eyes of consumers.  This breakdown is attributed to slow modifications to the conformation of proteins, leading to clumping phenomena.  Although the mechanisms underlying this instability are well known at high temperatures, INRA researchers have now studied this phenomenon at ambient temperatures.  They have demonstrated the combined impact of pH, ionic force and temperature on the onset of these protein disturbances.  Two paths can be followed in order to limit this phenomenon.  Firstly, it is possible to apply a fining treatment to the must; research has shown that this can lower the level of bentonite1, stabilise the wines without slowing down alcoholic fermentation (in fact, on the contrary), and above all reduce the undesirable effects of fining on the quality of the finished wine.  Another method is currently under development: specific elimination of the proteins that are responsible for this breakdown.  This work opens new perspectives regarding methods which could replace current stability tests and treatments.

1 Used for the fining of white wines, bentonite is a natural clay with a negative electrostatic charge that enables the adsorption of proteins with a positive electric charge.

The control of dissolved gases

Since winemaking first started, it has been known that oxygen plays a very important role in stabilising the colour of red wine and and the development of its aromatic notes.  Too much oxygen, and oxidation phenomena appear.  Insufficient oxygen, and reduction phenomena will develop, which may even product sulphur-based compounds with an odour reminiscent of rotten eggs....  After cork taint, these oxidation and reduction defects are the principal changes that can affect wine quality; hence the importance of controlling oxygen levels throughout wine production.  Today, recent technological advances have made it possible to measure oxygen levels at the different stages of winemaking.  At an experimental level, research has produced a tool that can control dissolved gas levels using a membrane technology (by raising or lowering carbon dioxide or oxygen levels).  Another INRA advance in the analytical control of dissolved gases consists in measuring oxygen levels by luminescence and carbon dioxide levels by laser spectroscopy, without affecting wine samples.

In addition, INRA is currently developing a cutting-edge innovation: the packaging of wines containing controlled dissolved gas levels, called Condinnov. This project involves studying wine in bottles or a bag-in-box2 system at an experimental scale of 20 to 100 litres on the one hand, and at an industrial scale of 10 to 100 hectolitres on the other.  With Condinnov, oxygen and carbon dioxide levels are adjusted by bubbling gas through the preparation vat (or in other words, through the liquid) and/or using a membrane contactor system.  A "line" has enabled the homogeneous bottling of experimental batches.

2 Bag-in-Box or BIB®: a widely-studied packaging system that takes the form of a bag filled with wine under a vacuum.

A new range of synthetic corks

Corks. © Fotolia
Corks © Fotolia
As both a lung and a filter, the cork allows the circulation of gases between the wine and the external environment.  Depending on whether this exchange is equilibrated or not, the wine will age well or poorly.  A short and porous cork facilitates these exchanges and activates ageing.  For great wines that are meant to be kept for many years under optimum conditions, very long, top quality corks are used. Another essential quality of a cork is its flexibility.  After being compressed during corking, it must be able to "re-expand" in order to seal the bottle's neck in an airtight manner.  In this area, INRA researchers and their industrial partner Nomacorc have studied the influence of the oxygen transfer rate on the sensory attributes of wines made using Grenache grapes during ageing.  A series of four synthetic, more or less hermetic corks was tested for 10 months on wines packaged in 375 millilitre bottles (the equivalent of about 20 months of ageing for a standard bottle of 750 millilitres). Their findings demonstrated the potential offered by the appropriate management of oxygen to encourage the expression of certain sensory attributes.  Based on these results, Nomacorc has pursued the development of a new range of synthetic corks that are classified according to different oxygen transfer rates.

An innovative and ecological packaging system

INRA is a partner in the Novinpak® project that was set up in 2009.  It aims to develop lightweight packaging systems for high-quality wines, based on recycled PET plastic.  This new packaging must comply with regulatory requirements and be adapted to the demands of both consumers and distributors.

Wine and health

Is drinking wine good for your health?  This is a thorny problem.  In France, wine accounts for two-thirds of all the alcohol consumed by individuals.  Twenty years ago, the concept of the French paradox was born of the observation that despite identical risk factors, French people benefited from better cardiovascular health than their neighbours in northern Europe or among Americans.  International studies focused on certain components in wine (such as particular polyphenols) and suggested their protective effects on our cardiovascular system.  But it is not that simple, because the cardiovascular health of an individual results from both genetic and behavioural factors, such as diet, physical activity, alcohol consumption or smoking, etc.  
In the context of this complex relationship between wine and health, cancer has been the subject of numerous studies which have shown that the risk of onset of a cancer (upper airways, colon, breast or liver) increases statistically significantly as from an average consumption of 10 grammes of alcohol (or one standard glass) per day.  The risk increases in line with the amount of alcohol consumed.  INRA and INSERM researchers studied the consumption of alcoholic beverages, including wine, by 29,566 adults belonging to the NutriNet-Sante cohort.  They demonstrated that the share of wine in alcohol intake increased in line with age and income, and observed that people consuming more than 10 grammes of alcohol per day cumulated more risk factors for cancer (e.g. age, smoking, excess weight, sedentary lifestyle, poor diet, etc.) than those consuming less alcohol.  This observation demonstrates the importance of increasing efforts with respect to prevention.

The Pech Rouge Experimental Unit

With its experimental facilities and different installations (winemaking unit, microbiology, delayed fermentation, extraction and separation techniques, ageing, etc.) - covering a total of nearly 5000 m2 - the INRA Pech Rouge Experimental Unit (Montpellier Research Centre) based in Gruissan near Narbonne is the focus for the transfer by INRA for all findings that affect winemaking and the vine-grape-wine continuum. Its mission: to innovate in collaboration with the Sciences for Oenology Joint Research Unit (Montpellier) and coordinate the dissemination of information to development agents.  To achieve this work, the Experimental Unit runs a 170-hectare estate (40 hectares of which is planted with vines) that also contains analytical laboratories, technological tools and finally a Sensory Analysis Laboratory which enables the tasting of different wines.


Corked wine?

Most blame for this combined odour of mould and wet cardboard can be laid on cork.  This natural product, made from the bark of the cork oak, is endowed with all the essential qualities necessary to close a bottle: airtightness, flexibility and porosity.  However, natural cork may also be partly responsible for cork taint, because of the presence of a compound that can develop in the bark of the cork oak: trichloroanisol (TCA).  Studies have revealed other possible reasons for cork taint: wooden barrels, conditions during shipment, etc.

Elevage du vin. © INRA, Christophe Maitre

Focus on aromas

Tertiary aromas

Vanilla, coconut, spicy or toasty aromas after ageing in oak barrels; chocolate, prune or walnut aromas with some naturally sweet wines; leather, animal or earthy aromas in some bottled wines.  These tertiary aromas develop while wines are aged in vats, barrels or bottles.  Generation of these aromas is closely linked to the oxidation-reduction reactions that occur in wine.  For this reason, the presence of higher or lower levels of oxygen, and how it penetrates into the wine, play a crucial role.