Studies On The Improvement Of Domestic Malt Quality By Microorganism Technique

Malt was one of the most important raw material of beer brewing and it was also one part ofthe beer raw material cost. It was microorganism-malting that had made a great progress onmalting in recent years. This paper was focused on improving the modification of domestic maltfor it's poor quality by using microorganism-malting. The main conclusions were as follows:1. The β-glucanase and xylanase activity of final malt was improved by pitching the spore ofRhizopus oryzae, Rhizopus chinensis and Rhizopus nigricans during steeping, β-glucancontent was decreased at the same time. While this two enzymes activity were not improvedby pitching the spores of Rhizopus arrhizus. Finally the Rhizopus chinensis was choosen asthe best one for microorganism-malting according to the food safety and spore yield.2. The optimal condition of spore production in solid-fermentation medium was studied. It wasshowed that the substrate was cooked bran which was passed 20 screen, the ratio of substrateto water was 1:1.4, initial pH was 6.0, the spore pitching volume was 10⁶/g bran, after 7-dayculture at 30℃, the spore production yield was reached 10⁹/g bran. The spore amount was400kg per year with 40000 ton malt production. It was proved feasibly in malting house.3. The microorganism-malting technique was researched primarily with domestic barley as theraw material. It was showed that the optimal pitching volume of Rhizopus chinensis activespore was 10³ï½ž10⁴/g dry barley in the first steeping water, 30℃ for 5 hours at the end ofgermination and abraded barley was helpful for the microorganism growth on the barley. Theβ-glucanase and xylanase activity was increased obviously in the microorganism malt;andthe malt quality data was improved. It was also showed by the organic acid content analysisthat the content of citric acid and malic acid was increased by 18.4% and 16.2%, respectively,and the content of amber acid and lactic acid was decreased by 19.3% and 24.2%,respectively in the microorganism-malt. It was meant that the organic acid inmicroorganism-malt was benefit for the beer flavor.4. The microorganism-malting mechanism was studied primarily. On one hand, the hyphae ofRhizopus were penetrated through the malt layer. The barley endosperm cell wall wasdegraded by the enzyme which was secreted by the microorganism directly. On the otherhand, the breathe character of malt had been improved by the penetrate ability ofmicroorganism. It was also benefit for malt modification. The quality of microorganism-maltcould be effectively improved by using abraded barley.5. The higher the protein content in barley was, the higher the β-glucan content in barley was,but the β-glucan content was not high certainly in final malt. There was positive correlationbetween the protein content in barley with α-amino nitrogen content, soluble nitrogencontent and protenase activity in final malt. But there was negative correlation between theprotein content in barley with extract content, Kolbach value and total polyphenol content inmalt.6. For domestic barley with high content of β-glucan and protein, the malt modification couldbe improved by adding protenase, NaOH+CaCl₂ and active spore in the steeping water. Butthe final malt quality was the best by using microorganism malting technique. The Kolbachindex was increased by 6.9%, β-glucan content was decreased by 42.9% in the final malt.