Fermentation with unfermentable sugars to improve the palate fullness and oxidative stability of beer

THOMAS KUNZ (1), Eon-Jeong Lee (1), Frank-Jürgen Methner (1)
(1) Berlin Institute of Technology (TU Berlin), Department of Biotechnology, Chair of Brewing Sciences, Berlin, Germany

Several breweries use unfermentable sugars to increase the beer palate fullness. Besides the direct addition of sugars to the final beer, it is a standard custom to add these sugars at the end of the wort boiling process prior to fermentation; especially for low-solubility sugars. The aim of this study was to investigate influences of the addition before fermentation of commonly used unfermentable sugars (polydextrose, palatinose, and trehalulose) in direct comparison to fermentable sugars (glucose and sucrose) on the fermentation process, palate fullness, beer flavor, and SO2 formation. The amount of sugar (fermentable and unfermentable) added to basic wort (10.5% original gravity) was calculated to achieve a realistic increase in final extract of 1, 2, 3, and 5%. Control fermentation with no sugar added (10.5%) and 12% extract was also performed. The fermentations were carried out simultaneously and under the same conditions. Yeast growth, SO2-production, extract, and pH development of every trial was monitored. After fermentation and filtration, the beers were analyzed (viscosity, extract, pH, color, SO2 content, etc.). Additionally, a trained sensory panel tested every trial with special focus on palate fullness, sweetness, and flavor in direct comparison to the control beer where 0% sugar was added (pilsner type). In comparison to the control fermentation, a higher SO2 formation was generally observed in the brews where no sugar was added. Sugar additions (fermentable and unfermentable) up to 1–2% yielded a significant increase in SO2 content. Compared to unfermentable sugars, higher glucose and sucrose additions (>2%) resulted in higher SO2 contents of the finished beers. It seems that the general increase in SO2 is based on the osmotic pressure change in the wort. Besides this, the addition of fermentable sugars leads to a higher SO2 formation because of a stronger increase of the yeast cell number at beginning of fermentation. At higher sugar concentrations (2–5%), the SO2 formation preponderates at the beginning of fermentation during the exponential growth phase of the yeast. This correlation is confirmed by the different influences of unfermentable sugars on the SO2 formation. With respect to the trials with unfermentable sugars, it could be observed that the addition of polydextrose leads to a diminished SO2 formation compared to palatinose and trehalulose mainly due to the smaller influence of polydextrose on the osmotic pressure of the wort. In summary, the results show that the addition of unfermentable sugars to 2% leads to a better palate fullness and higher concentration of antioxidant substances like SO2 without a detectable influence on the beer flavor or sweetness.

After qualifying as a certified technician in preservation engineering (1991–1993), Thomas Kunz completed his basic studies in chemistry at the University of Applied Sciences, Isny (1994–1995), and his basic studies in food chemistry at Wuppertal University (1995–1998), before starting to study food technology at the University of Applied Sciences, Trier (1998–2002). After graduating, he worked as a chartered engineer in the area of ESR spectroscopy at the Institute of Biophysics at Saarland University (2002–2004). Since 2005, he has been employed as a Ph.D. student at the Research Institute of Brewing Sciences, Berlin Institute of Technology (Technische Universität Berlin). His main research focus lies in analyzing radical reaction mechanisms in beer and other beverages using ESR spectroscopy.

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