Background. Beer refermentation is a preservation method that involves additional fermentation in a closed container. The condition for refermentation is the presence of fermentable sugars. The process is initiated by brewer’s yeast, which is present in beer or added intentionally to it. During refermentation, yeast uses sugars, producing alcohol, and CO₂, and at the same time, oxygen, which is responsible for adverse oxidation changes, is consumed. The aim of this study was to assess the usefulness of Saccharomyces cerevisiae var. boulardii CNCM I-745 (S. boulardii) yeast for wheat beer refermentation. Beer was produced using WB-06 yeast, which was then separated by microfiltration. The obtained base beer was poured into bottles and inoculated with S. boulardii at three levels: 0.1 %, 0.5 %, 1 %. Glucose was used as substrate for refermentation. The refermentation of test beers prepared in the aforesaid manner was carried out for 12 days at 22 ℃, and subsequently, the beers were placed in a cold room for 90 days. Beers without glucose were control. During the refermentation and storage of beers, S. boulardii number and physicochemical parameters (alcohol, apparent and real extract, pH, color, bitterness, reducing sugars) were controlled.
Results and conclusions. The results achieved indicate that refermentation of wheat beer with S. boulardii allows to obtain a product with physicochemical parameters typical of the style. Moreover, the use of this yeast in the refermentation process made it possible to obtain a product having probiotic characteristics. It was demonstrated that the best beer variant in terms of the survival of S. boulardii was B-0.1, i.e. beer inoculated with 0.1 % yeast inoculum and a glucose addition. In this beer, the yeast number remained stable (5.8 ÷ 5.9 log cell/cm³) from the 7th day of refermentation to the 90th day of cold storage.