The Microbiology of Wine Making, Essay Example

Introduction

Wine is produced with the help of yeasts called saprophytes; they represent the fungi living on dead or decaying organic material. Their name has a Greek origin with “sapro” meaning “rotten”. Since the time saprophytes were discovered they were found to depend on the dead plant or animal in the source of nutrition and energy of the metabolic kind. They do not perform the process of photosynthesis, thus not producing chlorophyll. Consequently, they are dependent on the decaying material on which they live and help it rot, without getting food energy from anywhere else (Basic Winemaking and Enology, n.d.).

Wine is produced due to the process of controlled fermentation that is known since ancient times; however, the genuine role of microorganisms called yeasts in this process has not been studied until the 1687 studies of Anton van Leeuwenhoek of Delft who was using the microscope to analyze and draw the images of bacteria, protozoa etc. and was the first to describe yeasts. In 1866 another breakthrough in understanding winemaking was made by Louis Pasteur. His studies were caused by the high percentage of wine spoilage, so Pasteur succeeded in explaining the major processes occurring during wine fermentation and even proposed some steps to increase the quality of wine production. Since then much has been discovered in microbiology of wine and beer production and the role of yeasts in this process became a widely researched phenomenon (Basic Winemaking and Enology, n.d.).

Throughout the 20^th century wine production grew considerably, especially with almost double figures for the US. Table wines became more complicated in the production processes, and more popular than dry wines; sterilization issues were worked out well. But the 1990s were marked with the innovative use of yeasts and bacteria, with new methods of maceration, thus causing the new problems of wine spoilage. Consequently, understanding basic rules governing winemaking, the importance of different bacteria and yeasts in the process as well as the main differences evident in the red and white wine production acquire specific importance in the 21^st century winemaking process.

Microorganisms Important to the Winemaker

The main microorganisms that take part in winemaking are molds and yeasts. Speaking about molds, one should understand the basic microbiological characteristics thereof. Molds are multicellular, filamentous fungi; they are saprophytes requiring the source of energy, and they grow in the form of a mycelium that is composed of hyphae (Zoecklein, 1995). These microorganisms occasionally are septate, depending on the organism on which they reside. Their reproduction methods are asexual:

“In most species, the asexual elements, or spores, are borne on specialized aerial hyphae termed sporangiospores or conidiophores, depending on the mold in question. Sporangiospores are conidiophores may be differentiated in that the former are normally protected within the body of a sporangium until dehiscence, whereas the latter are borne unprotected at the apices of conidiophores” (Zoecklein, 1995, p. 280).

The main importance of molds in wine production is that they provide for the fruit spoilage in the vineyard under certain conditions, thus assuring the future wine palatability. In winery, they grow mainly on the surface of the cooperage or on the walls, any other porous surfaces. Usage of molds is not only beneficial but also risky in winery because in case molds spread outside the cooperage they may instigate a set of undesirable processes such as emergence of other metabolite processes, emergence of the unpleasant odor and flavor, which can finally make a negative impact on the overall quality of wine (Zoecklein, 1995).

In modern times the issues of mold growing on or in the cork are acquiring key importance in the assessment of wine quality. It is a common fact that all molds except Penicillium are intolerable to the high level of alcohol in wine, thus being unable to exist in the cork and develop. The presence of molds in wines are commonly connected with the carryover of the early processing stages or the contact of wine with non-hygienically kept equipment or containers in which wine is stored before being distributed.  After the thorough analysis conducted in the connection with kinds able to survive in wines it was found out that it is limited to “alcohol tolerant lactic and acetic bacteria and several species of yeast” (Zoecklein, 1995, p. 281).

Another significant element of winemaking is yeast. Their range of influences on wines is highly diverse, ranging from positive to the highly negative ones. Among nearly 500 species of different morphology known to the modern microbiology only 15-20 kinds thereof are connected with winemaking.  Generalizing the kinds of yeasts used in the discussed sphere, one should know the following kinds according to the peculiarities of their application:

• Yeasts take part in the alcoholic fermentation, spoilage and autolysis; they are also a significant element of deacidification;
• Killer yeasts play a role in the alcoholic fermentation and spoilage control;
• Lactic acid bacteria are important for malolactic fermentation, spoilage and autolysis;
• Acetic acid bacteria affect spoilage and stuck fermentations;
• Fungi are used with botrytized wines, for spoilage and corky taints;
• Bacillus, Clostridium spp. are used for spoilage only;
• Actinomyces, streptomyces spp. are applied for earthy, corky taints;
• Bacteriophages are used to disrupt malolactic fermentation (Fleet, 1993, p. 2).

There is a set of yeasts important to the winemaker – their presence can mark both positive and negative phenomena in wine making. For example, the film forming yeasts such as Pichia, Hansenula etc. survive the fermentative phase and grow by means of budding on the surface of wine, witnessing its bad quality or irregularities in the fermentation process. However, it is also important to mention the positive impact of yeasts such as Saccharomyces sp. – by means of asexual reproduction these yeasts are able to produce “syruped” fermentations that enable the production of alcohol levels in wines from 16% to even as much as 18% (Zoecklein, 1995, p. 283).

Differences in the Production of Red and White Wines

As it comes from the basics of winemaking, production of red and white wines is seriously different. The most common procedures undertaken during the process of wine production are shown on the following two figures.

Figure 1: White Wine Production

Note. From Wood, B.J.B. (1998). Microbiology of fermented foods, Vol. 1. (2^nd ed.). Springer.

Figure 2: Red Wine Production

Note. From Dharmadhikari, M. (2000). Red Wine Production (Part 1). Vineyard and Vintage View, 15(2), pp. 1-8.

As one can see from the tables represented above, red and white wine production are highly similar in the process and manner of grapes treatment. From the microbiological point of view, Figure 2 represents more detailed information about the process, which can be seen from the detailed description of fermentors used and the activities such as usage of heat and cooling are enumerated. Upon getting wine, both products are undergoing optional processes of malolactic fermentation, aging and fining as well as clarification with the final element of packaging to transport the final product to consumers (Wood, 1998).

Conclusion

Since wine is subject to a variety of microbiological reactions in the process of its production, one should certainly understand all physical and chemical reactions that take place in the process of winemaking and chemical indicators according to which wine is assessed. These indicators include hydrogen ion concentration (pH), alcohol and sulphur dioxide as well as sorbic acid presence; fumaric acid, carbon dioxide and pressure, nitrogen availability and biological control also represent vital factors that should be seriously considered in the winemaking process (Zoecklein, 1995). Which is also important in winemaking is to realize that the taxonomy of microorganisms taking part in the fermentation process is not stable, so constant research should be conducted to improve and innovate existing methods and procedures of winemaking, implement molecular and genetic technologies and to make thorough classification in terms of microbiological substances.

Modern winemaking recognizes the need for distinguishing strains of various winemaking microorganisms, so the major trends of research at the present period of time constitute electrophoretic profiles of chromosomes, restriction enzyme digests of nucleic acids etc. (Fleet, 1993). Nowadays computer technologies are also applied to detect wine yeasts, lactic acid bacteria and enumeration of wine microorganisms, but surely these trends still represent a developing sphere and require much more information and research in the near future.

References

Basic Winemaking and Enology – 4 (n.d.). Retrieved March 30, 2010, from http://www.ccwinegroup.com/library/Basic_Winemaking_4.pdf

Dharmadhikari, M. (2000). Red Wine Production (Part 1). Vineyard and Vintage View, 15(2), pp. 1-8.

Fleet, G.H. (1993). Wine Microbiology and Biotechnology. CRC Press.

Wood, B.J.B. (1998). Microbiology of fermented foods, Vol. 1. (2^nd ed.). Springer.

Zoecklein, B.W. (1995). Wine analysis and production. Springer Science & Business.