Part I. The use of Lactobacillus plantarum starter cultures to inhibit rootlet growth during germination of barley, reducing malting loss, and its influence on malt quality

The reduction of malting loss has been an ambition for many decades, with the aim to achieve higher yields in the malting process. Organic acids have been shown to possess restricting effects on rootlet growth if exceeding critical concentrations. Lactic acid bacteria are able to produce high amounts of organic acids. In the present study, the potential of a broad selection of Lactobacillus plantarum strains as starter cultures to reduce malting loss and their subsequent impact on malt quality were examined. Starter cultures were prepared in a modified de Man, Rogosa, and Sharp medium and added to the grain immediately after steeping. A chemically acidified solution was added to mimic the impact of acids produced by the L. plantarum strains on rootlet growth suppression. The bacterial fermentation broths of all L. plantarum strains tested reduced malting loss to a similar extent accompanied by lower friability values and increased β-glucan contents. Malting loss could be reduced from approx. 7.3 to 2.3%. Resteeping in the chemically acidified solution reduced malting loss to approx. 3.5%. In both cases, the reduction in malting loss was accompanied with lower enzyme activities, in particular α-amylase, limit dextrinase, and β-glucanase. Although the quality of malt produced with reduced malting loss was diminished compared with control malt, parameters such as soluble nitrogen, free amino nitrogen, β-glucan, and friability were still in a range that can be seen as sufficient for brewing purposes.