Mr. Dr. George Cojocaru, Lecturer at the Faculty of Horticulture, within the Bioengineering of Horticultural Systems department, gave us an interview in which we covered the recent development of the oenological field in Romania as well as future technological trends. The discussion also includes details related to glass packaging and its impact on the winemaking process. We invite you to read it below:


How do you feel the oenological field has developed in Romania in recent years?

First of all, there appeared democratic organizational bodies and principles such as ONVV, ONVPV, ADAR, APIA, AFIR, wine producers’ associations and others. In the field of oenology, there has been a lot of investments in recent years, both in vineyards and wineries. New plantations were established with varieties, especially for quality wines. They allowed the implementation of technologies in vineyards aimed at mechanizing of the work and reducing manual interventions. In the wineries, technological flows have been modernized, and investments in stainless steel containers, temperature control systems, and modern equipment allow rigorous control of the processes. All this is reflected in the quality of the wines, as evidenced by the gold medals won by Romania at international wine competitions. The lack of national policies to promote this field, but also, the disinterest of some producers, makes us less known internationally. Relatively small wine exports explain this compared to other countries or the global average. Romania exports less than 5% of its wine production, although it should export >20-30% of its production. Countries with a tradition in this field export between 30-40% of production, and globally wine exports amount to more than 40% of production.

From your experience, what are the most common mistakes that wine producers in Romania are exposed to? Where do you feel wine producers are struggling?

Wine producers have invested a lot in wineries and vineyards, but in several situations, an essential thing has been omitted, the self-control of quality, the laboratory with the specific equipment, and the personnel in the laboratory. Process control and correct decisions are made based on a well-equipped laboratory, and, the total outsourcing of laboratory services is not yet a viable option in Romania. Suppose we refer to the quality of the wine. In that case, it is controlled primarily by obtaining quality grapes, which is not only reflected by the physical appearance, but especially by the physical-chemical composition given by a series of pedoclimatic factors, but also by the grape-growing technology.

The assessment and control of the quality of grapes is a first step towards quality wines, these include a series of laboratory analyses and sensory assessments to correctly decide the harvest date but also to correctly assess and manage deficiencies or excesses in grapes during the wine-making process. The most frequent mistakes during vinification arise from the lack of information provided by the laboratory and from the decisions made in a very short time without a scientific foundation. In most cases of decision failure, the problems can be corrected along the way in the production process. In these conditions, some wines that could have been exceptional, end up just impersonal wines, without noticeable faults. Another more acute problem than the actual production of wine is represented by sales. An exceptional quality wine is certainly easier to promote and sell than an average wine, but any packaging that does not tell a story, it will make the wine extremely difficult to sell. To this end, the marketing budget and the strategies implemented play a very important role in the success of the company.

Do you think Romania has found its own style in winemaking? Is it different from the different models offered by other countries?

There are different approaches globally regarding winemaking in countries with traditions that are part of the “old world” of wine versus countries that are part of the “new world” of wine. Although Romania is a country that is part of the “old world” of wine, by the simple fact that in the Carpathian-Danubian-Pontic space there has been wild vines since ancient times, the technological and marketing approaches are closer to what what is happening in the “new world” of wine.

Collectivization and the visions of the communist regime in Romania made us today to be somewhere between the two worlds. There are some major differences regarding the winemaking approach because we have to take into account that more than 95% of the wine production represents domestic consumption, so the wines are produced for the taste of the Romanian consumer. Things will gradually change because on the Romanian wine market, there are more and more imported wines of very good quality, with very good prices, and consumer preferences are gradually changing as they consume other wines.

We are talking more and more often about topics such as precision viticulture and oenology, which involve a series of modern technologies in which sensors and programs are used to collect and analyze various data in real-time in order to provide decision support regarding treatments and certain activities in the vineyard or even in the winery.  These decision support systems have developed a lot in recent years and almost all production stages may be monitored and managed with their support, so they can reduce working time, substances used, and especially decision-making, thus, can increase productivity, economic efficiency and product quality. There is, however, an international trend to convert grape-growing surfaces to organic production as, organic grape-growing areas have reached more than 6% of the total grape-growing surface.  

On the other hand, there is a global concern for grape varieties with genetic resistance to diseases and abiotic stress. These new varieties are obtained through several generations of interspecific backcrosses between different species with certain resistances of the genus Vitis sp. and the noble Vitis vinifera varieties. In the end, it is desired that the Vitis vinifera genome to represent as much as possible and that the wines to be no different from the traditional ones obtained from noble varieties. These research programs aim to reduce the use of pesticides. It is not excluded that in the coming years, important surfaces of these varieties will be planted and commercial wines will be produced from varieties that we have not heard of in the past. Another important aspect is the fact that only 85% of wine production is represented by consumption during the last 20 years, and, the surplus of wine every year and the worldwide trends of decreasing consumption per capita, could lead to a considerable decrease of the surfaces cultivated with grapes in some countries.

People involved in the winemaking process know this aspect quite well, specifically the link between oxygen and different winemaking stages (processing, storage, maturation, or aging). Just as an apple cut in half and left on a certain amount of time (Figure 1.A and Figure 1.B), oxidizes and the color turns into brown, wines exposed to different oxygen concentrations undergo a slower of faster oxidizing process.

Figure 1. Freshly cut apple (A) and cut apple after 2 h exposure to oxygen (B)

A small degree of oxidation may be necessary for the wine to mature and become more pleasant from a sensory point of view. White and rosé wines need as little as possible exposure to oxygen, being more susceptible to oxidation, while, red wines generally need more exposure to oxygen to be able to increase in quality. Storing red wines in oak barrels ensures micro-oxygenation through the pores of the staves.

Oxygen changes the structure of the polyphenols in the wine, so they become more stable and less inclined to subsequently affect the wine’s clarity, but through this process, they also acquire some sensory characteristics highly appreciated by consumers. However, it should be noted that after bottling, the oxygen exposure of wines is drastically reduced. From this moment the type of packaging and the closing system are the elements that control this process. However, there is an idea in the minds of some consumers that older wines are better, but this is partially true in the current context. Aging of wines is a stage in the wine’s life that begins from the moment the wine arrives in the bottle until, from a sensory point of view, it reaches its maximum quality, which remains constant until the inevitable moment when degradation occurs. The speed of these stages in the wine’s development are carried out depends on several factors such as the variety, the style and technology of winemaking, the degree of exposure to oxygen and the storage conditions before bottling, and also after bottling. The consumer must realize that the wines sold today are designed to be more quickly consumed, in 1 to 5 years, and, not to be kept for another 20 years. Strong wines, designed for aging, do not reach their maximum quality from a sensory point of view if they are consumed shortly after bottling. Bearing in mind that bottling and storage involve some high costs, and producers have to be prepared from one year to another for a new harvest, we can realize that old wines cannot represent to much of the amount of wine produced that year.

One thing is certain, oxidation-reduction processes are constantly happening in wines no matter what stage they are in, but they are mainly driven by oxygen concentration and temperature. To be able to better exemplify oxidation in an image (Figure 2), we reproduced the oxidation of a white wine under different conditions of exposure to oxygen.

Figure 2. The effect of oxygen on the color of a white wine: the numbers indicate the oxygen saturations the wine has been exposed to.

The figures show what happens to a white wine by exposure to 0, 1, 3, 9, and 27 oxygen saturations. This test is extreme, but it can help us better understand what happens through repeated exposures to oxygen. An oxygen saturation of wine is about 10 mg/l of dissolved O2. Producers must properly manage oxygen exposure throughout the life of the wine in relation to the type of wine.

What can producers do to have more control over this process? Can they determine the air transfer of the cork? What should they look out for?

The control over redox processes in wine is influenced by numerous factors (knowledge, available technology, type of wine, etc.). Producers need to be careful about how much oxygen they use when maturing their wines, they need to exclude dissolved oxygen as much as possible during bottling, and of course, they need to pay special attention to the quality of the cork. Personally, I encourage the producers to choose a cheaper bottle and a quality cork instead of an expensive bottle and a cork of questionable quality. I say this because glass is impermeable to oxygen and is a chemically inert material, but the cork is not. The natural corks are classified according to quality categories depending on their surface imperfections. The more these imperfections exceed 4-10 mm2 on the cork surface, there is a considerably higher risk for the appearance of the cork taint but also the possibility for increasing the oxygen transfer rate which can lead to some undesirable oxidation phenomena.

At the same time, the producers must take into account that the cork must be more than 5.5 mm wider than the neck of the chosen bottle, and the length of the cork must be correlated with the ullage in the wine bottle. The ullage or the space between the wine and the cork must be less than 2 cm. For the wines intended to be kept for longer aging periods, the corks must be at least 45 mm long and better quality. The oxygen transfer rate (OTR) can also be determined at the wine cellar, but the necessary equipment involves some costs and these results may not be very useful for the producer. Determining the OTR is more important for the manufacturers of packaging and closure systems who need to test and develop new closure systems. Batches of corks of varying quality are a problem because in the same bag there are relatively good corks, but also corks with too many imperfections. In the end, everything starts with the cork producers, because they have to sort them accordingly to quality category  to reduce the variability as much as possible. Wine producers must be careful to select the best possible quality of natural corks and dimensions in relation to the glass used. There is one unwanted phenomenon that occurs at bottling and the winemakers often blame the corks, but in reality, it is not entirely true. Forcing the cork through the bottle neck during bottling leads to an increased pressure inside the bottle and also an increased amount of oxygen, but, even worse, this makes the wine leaks out of the bottle by turning bottles to horizontal position.

For these reasons, modern corking machines are equipped with a system for creating a partial vacuum in the bottle before the cork is inserted. The ideal internal pressure after corking of still wines should be 0 bar, but in good cases, it is ±0.2 bar. When the pressure in the bottle increase over 0.2 bar, the aforementioned problems can occur. If the internal pressure is high, the bottles can be kept upright for 1-2 days to allow the pressure to decrease and the cork to return to its original size.

Glass containers for packaging are very diverse in shape, size and colour, which allows producers to personalize their wine and give it a special appearance. Probably the first thing that many consider is how they recover the price of the packaging through the price of the product sold. When we choose a certain type of glass container, we must take into account whether the existing equipment is compatible with that model. The shape and dimensions of the glass can affect the normal operation of the equipment, truncated-cone shape bottles can overturn, those that have diameters that are either too small or too large or the height in relation to the dimensions for which the equipment was designed, will generate more problems. Many times, for the bottling of limited edition wines, manual bottling is often used because those containers have more special shapes or sizes. Glass containers can be adapted for other closure systems than classic stoppers, including: glass stoppers fitted with a gasket specially designed for low permeability to oxygen or various metal caps. The color and thickness of the bottle can, to a certain extent, affect the oxidation-reduction phenomena and also the longevity of the wines. For example, white and rosé wines are bottled in transparent glass containers to make them more attractive to the consumer, but if we wanted to provide some protection from exposure to light, thicker dark green or even brown bottles would be a better option.

Transparent glass has in its percentage composition approximately 70% silicates, 15% sodium oxide and 7% calcium oxide, 3% magnesium oxide, 2% aluminum oxide as well as some impurities such as iron oxide. Although it appears colorless to the naked eye when thin, iron oxide impurities produce a green tint that can be seen in thicker layers or through laboratory instruments. Discoloration of glass is a method by which pigments are added to the manufacture of glass with a greenish tint to create an apparently colorless product, but this will decrease the transparency of the resulted glass. To change the color, some metals and metal oxides are added during manufacture. Manganese dioxide is used to remove the green tint given by iron. Green bottles are usually obtained by adding chromium oxide in the manufacturing process. Other chemicals can be added to produce different shades of green (eg: iron oxide II – blue-green). Generally, wine bottles contain chromium oxide in varying concentrations. By increasing the concentration of chromium oxide, the glass can acquire a very dark shade. Very dark and thicker tinted glass is considered better for protecting the wine from light exposure, but under uncontrolled storage conditions (eg: exposure into the sun), these bottles can accumulate more heat and cause more problems for the wine compared to a thinner bottle and a lighter color.

Dark brown bottles are made by mixing sulfur, iron, and carbon into the basic glass formula. By adding these substances, iron polysulphides are formed which produce shades from yellow to dark brown. These bottles are useful when the product is more sensitive to light. The dark brown color absorbs UV light, thus protecting the product. Because of this, dark brown bottles are commonly used for beer, some medicines, essential oils, and why not, wines. Blue bottles are produced by adding cobalt oxide in a concentration of 0.025 to 0.1% in the manufacturing process. This process results in a blue glass of varying intensities. Cobalt oxide is an extremely strong dye, which is why a few parts per million are sufficient for coloring. Blue bottles are not very popular for storing wines because they gives less UV protection compared to the other colors and, gives a protection close to clear glass.

However, manufacturers can take into account that there is a worldwide focus on reducing the carbon footprint of finished products, and in this case, reducing the weight of glass containers could significantly reduce carbon emissions. Glass production and the manufacture of glass containers contribute over 45% of the carbon emissions of a 750ml bottle of wine. Studies show that by reducing the weight of glass containers from an average of 550 grams to 420 grams, carbon emissions for a 750ml bottle of wine can be reduced by up to 10%. In many situations, producers choose heavier bottles with a higher degree of customization with respect to the work and the quality of the bottled wine, but in the coming years, this not-so-environmentally-friendly trend may change.