Enology

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 directive1 due to the repercussions it may have on consumer health. As a result, there is a tendency for winemakers to adopt new disinfection methods that represent lower expenditure in terms of resources and greater security for both the operators and consumers2. Near ultraviolet radiation (UV-C) is a technique currently applied for activities such as water disinfection or the sterilisation of workspaces that have smooth surfaces. Empirical experiments conducted on the disinfection of barrels have also shown that after racking and cleaning the interior of the barrel with pressurised hot water (using equipment by Kärcher Spain) at 80 °C for 20 min, a UV-C transmitter can be used for 15 minutes to disinfect a 225 L barrel3. The aforementioned study lacks scientific information regarding the effects of UV-C radiation on the population of microorganisms.

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 bacteria4). In each experiment, the sampling was carried out before and after each of the following treatments:

. 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 treatment5). Our study also shows that the populations of yeasts or of acetic acid bacteria are strongly reduced by the combined 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.

Authors


Maria C. Portillo

carmen.portillo@urv.cat

Affiliation : Group of Oenological Biotechnology, Rovira i Virgili University, Faculty of Oenology, Biochemistry and Biotechnology Department, Marcel·lí Domingo 1, 43007 Tarragona, Catalonia

Country : Spain


Erick Alberto Tena-García

Affiliation : Group of Oenological Biotechnology, Rovira i Virgili University, Faculty of Oenology, Biochemistry and Biotechnology Department, Marcel·lí Domingo 1, 43007 Tarragona, Catalonia

Country : Spain


Eugenia Vila

Affiliation : E.Vila Projects & Supplies, c/Rasos de Peguera, 28, 08272, Sant Fruitós de Bagés, Barcelona, Catalonia, Spain

Country : Spain


José M. Rigol

Affiliation : Automatismos Arapiasa, SL, C/ Pobla, 223, 08788, Vilanova del Camí, Barelona, Catalonia

Country : Spain


Nicolas Rozès

Affiliation : Group of Food Microbial Biotechnology, Rovira i Virgili University, Faculty of Oenology, Biochemistry and Biotechnology Department, Marcel·lí Domingo 1, 43007 Tarragona, Catalonia

Country : Spain

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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