Sanitisation of wine-ageing barrels using near Ultraviolet radiation Original language of the article: English.
The ageing of wine in oak barrels represents a critical stage in winemaking at which product alteration can occur due to bacteria, yeasts or fungal growth. The control of microorganisms, such as yeasts of the Brettanomyces genus (Guzzon et al, 2011) and acetic acid bacteria (Kocijan et al, 2021), is of great importance, since the alterations that they can cause in wine can be very serious and cause great economic losses.
Currently, the application of good disinfection practices can adequately control the proliferation of microorganisms in barrels, and thus prevent the alteration of wine. One of the most widely used methods is the burning of sulfur wicks, which releases sulfur dioxide (SO2). However, its use is limited by a European Union directive
In the present study, the germicidal potential of UV-C radiation applied to the interior of barrels used for wine-ageing was evaluated; for this purpose, a prototype was designed by the companies E. VILA PROJECTS & SUPPLIES S.L. and AUTOMATISMOS ARAIPIASA, S.L.
Material & Methods
The experiments were performed using 9 oak barrels (225 L) that were 5 to 6 years old and from different manufacturers (3 Cadus, 2 Billon, 2 Groupe Vicard, 1 Torner y 1 Damy). The barrels were randomly numbered from 1 to 9 and put into three groups of three barrels each. Six of the oak barrels were inoculated with Brettanomyces bruxellensis using 20 L of water with a final concentration of 1x106 CFU/mL (previously grown on liquid YPD up to 1x108 CFU/mL). This water was distributed within the barrel by periodical shaking and rotating for the next 7 days. The other 3 barrels were kept as uninoculated controls. Then, the barrels were emptied and sampled for microbiological analysis. The sampling of culturable yeasts and bacteria in the barrels inner surface was carried out by introducing 20 L of water at each of the 9 barrels. After thoroughly shaking and rotating the barrels, a sample of 1,5 L of water was taken using a vacuum pump, sterile tubes and kitasato flasks. Finally, dilutions of these samples were plated by triplicate on different culture media (YPD agar medium for total yeasts, Lysin agar medium for non-Saccharomyces yeasts and GYC agar medium for acetic acid bacteria
. Treatment 1: Application of pressurised hot water (150 ºC, 75 bars, 1 min, Kärcher HDS)
. Treatment 2: Application of UV-C radiation using an ozone-free UV-C lamp with amalgam emission, (253,7 nm, 130W). Prototype designed by the companies E. Vila Projects & Supplies S.L. and Automatismos Araipiasa, S.L.
. Combination of Treatments 1 & 2.
Results
Effect of the treatment on the reduction of the total yeast population in barrels
The treatments applied to each group of barrels were the following: application of pressurised hot water for 1 min (Treatment 1), application of UV-C radiation for 10 min (Treatment 2), a combination of Treatments 1 & 2, hot water at pressure for 1 min and subsequent treatment with UV-C radiation for 10 min (Figure 1). In Figure 2 the effects of separate or combined treatments are shown. All treatments induced a significant reduction (an average of 1.46 log10 CFU/mL) in the total yeast populations before and after treatment. However, when a second UV-C treatment of 10 min was applied after the water treatment, the total population in yeast decreased and was significantly different from the first result (p < 0.05 according to the Fisher LSD Test) (Figure 2). The results for CFU in the LYS medium were not significantly different from those in YPD, revealing that the detected yeasts were probably non-Saccharomyces yeasts.
Figure 2. Effect of treatment on the reduction of total yeast populations. Treatment 1, Pressurized hot water, 1 min; Treatment 2, UV-C 10 min. *, p < 0.05; ***, p < 0.0001 (Fisher, LSD).
In order to confirm these results, a replicate of this experiment was carried out two weeks later, in which the treatment was applied randomly to the barrels (Table 1). Once again, the results confirmed the effectiveness of the pressurised hot water treatment and of the usefulness of UV-C radiation treatment as a disinfection complement.
Table 1. Effect of treatments on the reduction of total yeast populations (log10 CFU/mL).
Pressurised hot water treatment |
UV-C (10 min) treatment |
Combined treatments |
|
|---|---|---|---|
Before treatment |
5.78 |
6.05 |
6.34 |
After treatment 1 |
3.361 |
4.981 |
4.171 |
After treatment 2 |
- |
- |
3.562 |
Significant differences |
p1 < 0.0001 |
p1 < 0.0001 |
p1 < 0.0001 p2 = 0.064 |
1 Significant difference between the first treatment and the initial value before treatment
2 Significant difference between the second and first treatment.
The results obtained for the plates containing GYC medium for the enumeration of acetic acid bacteria (Figure 3), show a decrease of 2,49 ± 1,04 log10 CFU/mL in the treatment with pressurised hot water, 1,17 ± 0,18 log10 CFU/mL in the UV-C radiation treatment and 3,69 ± 0,21 log10 CFU/mL in the combined treatments. This confirms the ability of the combined treatment to control the proliferation of these bacteria.
Figure 3. Effect of the treatment on the reduction of the populations of acetic acid bacteria. Treatment 1, pressurised hot water for 1 min; Treatment 2, UV-C for 10 min. NS, Not significant; ***, p < 0.001 (Fisher, LSD).
Effect of duration of UV-C radiation on the reduction of the microorganism population
In this experiment, the effect of duration of exposure to UV-C radiation was studied as a complement to the previous treatment of pressurised hot water. After receiving the latter treatment for 1 min all the barrels were treated with UV-C radiation for 2.5, 5 and 10 min in triplicate. The data of the counts in yeasts and acetic acid bacteria are shown in Figure 4. It can be seen that similar results were obtained for the exposure durations of 2.5 and 5 min, with approximately a 2.11 log10 decrease in the yeast population. On the other hand, a higher exposure duration (10 min) resulted in an increase in the effectiveness of the treatment, with a 2.58 log10 decrease in the population. This represents a yeast population reduction of approximately 50 % in logarithmic units and more than 99 % of the initial population in CFU/mL. However, the differences in the effects produced by the different treatment durations are not statistically significant.
Regarding the populations of acetic acid bacteria, we were able to observe a significantly positive effect of UV-C treatment time on the decrease in viable cells: from 3.40 log10 CFU/mL to 5.49 log10 CFU/mL for durations of between 2.5 and 10 min respectively (Figure 4).
Figure 4. Effects of treatment duration on the reduction of populations of yeasts and acetic bacteria. Pressurised hot water treatment, 1 min and UV-C, 2,5, 5 and 10 min. Yeasts: no significant effect of treatment duration (p = 0.075); Acetic bacteria: there is a significant effect of treatment duration (p = 0.006).
Conclusions
Our results show that it is possible to use UV-C radiation to disinfect barrels for a maximum of 10 min after a 1-min treatment with pressurised hot water. This combined treatment allows an effective level of disinfection to be obtained within a short period of time, providing benefits such as a reduction in energy consumption, water consumption and exposure to work-related risks (compared to previous literature describing similar population reduction for 30 min of each individual treatment
Funding: This research has been funded by the companies E.VILA PROJECTS & SUPPLIES, SL and AUTOMATISMOS ARAIPIASA SL.
Notes
- Reglamento delegado (UE) 2019/934 de la Comisión de 12 de marzo de 2019. Diario Oficial de la Unión Europea. L149/1 – L149/52.
- Stadler, E., & Fischer, U. (2020). Sanitization of Oak Barrels for Wine. A Review. Journal of Agricultural and Food Chemistry, 5283-5295. DOI : 10.1021/acs.jafc.0c00816
- Furet-Gaballet, C. (2019). Pleins phares sur les cannes à UV. La Vigne 317, 44-45. https://catalogue.albert-oenologie.fr/upload/products_data/files/Article%20Cannes%20UV%20La%20Vigne%20Mars%202019.pdf
- OIV (2021) Técnicas analíticas y de control microbiológico, análisis comunes a todas las monografías. RESOLUCIÓN OIV-OENO 632-2021. 12 de julio de 2021. https://www.oiv.int/public/medias/8103/es-oiv-oeno-632-2021.pdf
- Guzzon, R., Widmann, G., Malacarne, M., Nardin, T., Nicolini, G., & Larcher, R. (2011). Survey of the yeast population inside wine barrels and the effects of certain techniques in preventing microbiological spoilage. European Food Research and Technology, 285-291. DOI: 10.1007/s00217-011-1523-8.
References
- Guzzon, R., Widmann, G., Malacarne, M., Nardin, T., Nicolini, G., & Larcher, R. (2011). Survey of the yeast population inside wine barrels and the effects of certain techniques in preventing microbiological spoilage. European Food Research and Technology, 285-291. https://doi.org/10.1007/s00217-011-1523-8
- Kocijan, T., Bossaert, S., Van Boeckel, G., & De Rouck, G. (2021). Sanitation of wooden barrels for ageing beer - A review. Brewing Science, 51-62. https://doi.org/10.23763/BrSc21-04kocijan
- Reglamento delegado (UE) 2019/934 de la Comisión de 12 de marzo de 2019. Diario Oficial de la Unión Europea. L149/1 – L149/52.
- Stadler, E., & Fischer, U. (2020). Sanitization of Oak Barrels for Wine. A Review. Journal of Agricultural and Food Chemistry, 5283-5295. https://doi.org/10.1021/acs.jafc.0c00816
- Furet-Gaballet, C. (2019). Pleins phares sur les cannes à UV. La Vigne 317, 44-45. https://catalogue.albert-oenologie.fr/upload/products_data/files/Article%20Cannes%20UV%20La%20Vigne%20Mars%202019.pdf
- OIV (2021) Técnicas analíticas y de control microbiológico, análisis comunes a todas las monografías. RESOLUCIÓN OIV-OENO 632-2021. 12 de julio de 2021. https://www.oiv.int/public/medias/8103/es-oiv-oeno-632-2021.pdf
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