# The Influence of Fermentation Vessels on Yeast Microbiota and Main Parameters of Sauerkraut
## 1 Introduction  
Sauerkraut is the most widely produced fermented vegetable in the world. It is a food product obtained as a result of chemical changes occurring during spontaneous lactic acid fermentation carried out by the microorganisms originating from the surface of the vegetable leaves [1]. This microbiota occurs in a strictly defined order, determined by the changing conditions during pickling, and is responsible for transforming components from the raw material into substances important for the final product. The final quality of sauerkraut depends on many factors, such as the quality of the raw material, the initial level of contamination (depending on the conditions of growing vegetables), production hygiene, quality of starter cultures, fermentation conditions (time, salinity, and temperature), and the degree of acidity achieved. Maintaining all parameters at an optimal level for the fermentation process may be especially troublesome in the case of small-scale production, which is less automated [2].  
The conditions in which fermentation is carried out have a qualitative and quantitative impact on the microbiota present during fermentation and, therefore, also on the quality of the produced sauerkraut. In Poland, the most common addition is NaCl at the level of 2-2.5%, and fermentation is carried out in tanks (often concrete), in which the surface is often covered with a plastic bag filled with water. This is intended to isolate the cabbage during pickling from the external environment, but also by applying pressure, releasing the juice in which fermentation takes place [3]. Unfortunately, because this system is not perfectly tight, it causes oxygen to enter the tank, modifying the conditions during fermentation as well as the microbiota present. At the same time, it contributes to theintensive development of yeasts, especially film-forming ones, which change the chemical composition of the fermented vegetable. They use organic acids, stabilizing the product, mainly lactic acid, as a carbon source. This also leads to a decrease in acidity and an increase in pH, which can result in the growth of putrefractive bacteria and other spoilage microorganisms [4].  
Our previous research has shown that not all yeasts present during sauerkraut fermentation have a negative impact on its quality. We found that _Debaryomyces hansenii, Clavispora lustianiae_, and _Pichia fermentans_ cultures are detected during pickling regardless of the cabbage variety used, and may introduce components into the product that lactic acid bacteria (LAB) cannot synthesize. However, the research was conducted in anaerobic conditions, in which there are no yeasts with aerobic metabolism, which most often is a problem in the production of fermented vegetables [5].  
This work aims to compare the yeast microbiota that is present during cabbage fermentation depending on the vessel used. For this purpose, glass jars were used, in which anaerobic conditions are quickly created, and stonewarse vessels, whose appearance and characteristics are similar to tanks used on an industrial scale. Due to the micropores present in the walls, gases can penetrate the interior of the vessel, similarly to its cover, which is made of a plastic bag with a pressure stone placed on it. In addition to yeast, other basic parameters affecting the quality of the sauerkraut were also analyzed during fermentation and in the finished product, such as the amount of LAB, pH, the content of selected organic acids, sugars, and polyols, and FAN. Sensory analysis was also carried out.