Fermentation processes can and must be monitored and controlled so that no off-flavors occur in the subsequent product, deteriorating its quality. At the same time, certain aroma substances can be influenced (made stronger or weaker) by fermentation management whereby different wine styles arise. But even after fermentation processes, off-flavors in wines can occur during wine storage and even after bottling.
You can find below some assistance services provided by the department:
A comprehensive overview of how the fermentation process can be precisely analyzed using a microscope is provided by the book "Safe fermentation in the cellar" written by the Department of Microbiology and Biochemistry, and published by Ulmer, Stuttgart. Simple examination procedures are presented step by step and explained visually using sample images.
The book mentioned under “Monitoring alcoholic fermentation” also illustrates the essential features of targeted monitoring of MLF. First of all, it is important to be able to identify the existing type of bacteria by visual differentiation and thus to identify potential problems at an early stage: Pediococci and lactobacilli can cause problems in filtration and the formation of biogenic amines.
The storage and saleability of wines and sparkling wines are mainly determined by two parameters. This is on the one hand the absence of microorganisms of any kind that could cause secondary fermentation through metabolic activities and produce negatively evaluated substances and secondly the storage temperature.
Even in the absence of microorganisms, quality losses can occur in stored wines. The off-flavors that might occur are, for example, cork and moldy tones, even when using screw caps, as well as, for example, in Riesling wines, the occurrence of the so-called "petrol flavor".
In the area of microbiological analysis, our department offers:
- Sterile control of bottled drinks:
Reference values: less than five fermentable yeasts and less than 50 lactic acid bacteria per 0.75 l bottle - Determination of infectious microorganisms:
Identification by FT-infrared spectroscopy or PCR-techniques; decision on risk of secondary fermentation - Advice on the further procedure for non-sterile filling:
Gradual control of all devices and tubes involved in the filling process
and in the chemical analysis area:
- Detection of cork or moldy flavours:
also verification of non-wine beverages - Determination of sensory-active microbially-formed substances:
proof of esters, higher alcohols, acetic acid, etc. - Determination of SO2-binding substances:
primarily acetaldehyde, 2-keto-glutarate, pyruvate - Analysis of the acid spectrum of musts and wines:
first and foremost, tartaric acid, malic acid, forms of lactic acid, succinic acid, shikimic acid, etc. - Various analytical methods are available for the treatment of specific issues:
gas chromatography, partially coupled with mass spectroscopy, high performance liquid chromatography, photometry
The Department has had a yeast strain collection at its disposal since 1894, from which selected strains are sold as fresh liquid cultures to wine and sparkling wine companies.
Below you can find an overview of which yeast strains are available and how a liquid culture is further increased and used.
Pure yeast strains from Geisenheim
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