UV-C Treatment of Must and Wine to Inactivate M

As part of the AiF project, the effectiveness of UV-C in killing microorganisms in wine and grape must was investigated, and evidence was found that UV-C light could also be used for targeted wine aging. The goal of this research project is to build on the results of the IGF project AiF 18688 N and utilize UV-C technology as a combined process for the stabilization and aging of wine. To achieve this, the application of UV-C must be adapted to the chemical composition of UV-active wine constituents, the optical density, and the type and quantity of microorganisms in order to meet the stabilization and maturation objectives. The goal is to determine specific UV-C doses across various wavelength ranges and depending on the wine’s composition, at which no adverse changes in sensory properties or value-adding constituents are detectable, thereby ensuring that the quality of the final product is not compromised but rather optimized in terms of wine stability and maturation.

Ultraviolet light can cause irreparable damage to the DNA of microorganisms, thereby preventing cells from multiplying. Wavelengths between 250 and 260 nm (UV-C) are of particular relevance, as DNA strongly absorbs the irradiated energy in this wavelength range. Among other effects, this leads to the dimerization of thymine nucleotide bases and disrupts replication. The commercial application of the targeted inactivation of microorganisms using UV-C is known as UV-C technology, which is used, for example, to disinfect water or packaging surfaces. Regardless of whether liquids or surfaces are being treated, the disinfection effect occurs in the upper layers, depending on the penetration depth of the waves. In liquids, the effect depends on UV absorption by dissolved substances or by particles that reflect or scatter light. In turbid, absorbent liquids, no effect is detectable after just a few millimeters without mixing the medium. This problem can be circumvented by using suitable process technologies, such as specific reactor designs or flow patterns. The liquid can either be treated in a thin layer (thin-film reactors) or in spiral-shaped channels where intensive mixing of the liquid takes place (spiral reactors, turbulence reactors).

Preservation is a critical process in the food processing industry, ensuring that transportation, storage, and thus product availability can occur without significant changes to the food’s valuable nutrients. UV-C technology has been used and tested in the food industry for many years. Studies have also been conducted in the field of winemaking that highlight the benefits of this technology. For example, Saccharomyces cerevisiae and Brettanomyces bruxellensis in Chenin blanc were reduced by 5 and 3.5 log orders, respectively, using a UV-C dose of 1.4 kJ/L at a flow rate of 4,000 L/h. No changes in color or standard chemical wine parameters were observed as a result of UV-C exposure; however, concerns have repeatedly been raised regarding the potential impact of UV-C on wine aroma and shelf life.

The research project is being conducted as a collaborative effort with Prof. Dr. Dominik Durner and the Max Rubner Institute (MRI), the Federal Research Institute for Nutrition and Food (project leader: Dr. Mario Stahl).