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A Technical Guide for Wine Producers
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Wine and biotechnology
Gustav Styger, Institute for Wine Biotechnology
Many people think that the concept of biotechnology is completely alien and at odds with the ancient and natural “art” of winemaking. However, the whole tenant of winemaking, using yeast to convert sugar in the form of grape juice into ethanol in the shape of wine, is in fact one of the worlds oldest biotechnological processes!
The very fact that we use biological agents to convert a substrate into a product is the basic definition of biotechnology. This concept is called first generation biotechnology; basically the proof of concept stage. We all know that winemaking works very well and this is in a large part due to second generation biotechnological procedures. This entails the generation of better biological agents to perform the reaction, through the so-called classical microbiological techniques, such as breeding, mutagenesis and directed evolution. The discussion of these techniques will form the first few instalments of this column.
Yeast breeding
One of the oldest techniques employed to improve the yeast strains used during winemaking is yeast breeding. Laboratory strains of Saccharomyces cerevisiae has a sexual life cycle like other higher organisms, as shown in the figure. Cells can either be haploid, containing one set of chromosomes (n = 16), or diploid, containing a double set (2n = 32) of chromosomes. Diploids are formed when a-type haploids cells are mixed with alpha-type haploid cells. Both haploid and diploid cells can replicate asexually through budding.
Under certain stress conditions – particularly starvation – diploid cells can sporulate, resulting in the formation of asci containing four spores. These spores contain the haploid (n = 16) number of chromosomes and can germinate giving rise to two a-, and two alpha-cell cultures. Winemaking yeast strains are larger and genetically more complicated, with a polyploid (3n, 4n, etc.) number of chromosomes. Furthermore, they are heterozygous (carrying more than one type of a certain gene).
In order to obtain new yeast strains with unique characteristics it is important to select the parental strains correctly. Say for instance we have strain A that is able to ferment very fast and strain B which produces a positive aroma profile. Yeast breeding can then be used to combine the best characteristics of A and B into one strain. This is first done by sporulation of the two parental strains and the subsequent inter-crossing of the spore clones. This will form many new combinations of genes, possibly resulting in yeast strains with altered characteristics, some of which may be attractive to the winemaker.
However, because of the generalised and unco-ordinated way that the genetic material is rearranged during the mating process, many new strains will have none of the desired characteristics and some may even exhibit a few unwanted traits. Thus, it is very important to have a system in place where the new strains can be screened in order to determine whether they are in fact improved or not. In order to maximise this technique, high-throughput technologies like robotics are often used.
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