Methods for reducing the diacetyl content to shorten maturation time in brewing processes | |
| Author | Duong Thi Viet Nga |
| Call Number | AIT Thesis no.FB-04-01 |
| Subject(s) | Brewing Fermentation Beer |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resorces and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. FB-04-01 |
| Abstract | The main purpose of the study was to investigate ideal methods to reduce the diacetyl content in beer for rapid maturation. The first method was using Maturex, an α- acetolactate decarboxylase enzyme, at the beginning of primary fermentation to directly convert α-acetolactate into acetoin. The second method was accelerated maturation in a continuous, immobilized bioreactor system. In order to obtain the best conditions in each method, optimizations of the processes were done. It is known that diacetyl which causes an intensive and undesirable flavor for finished beer is an important criterion for determination the length of maturation process. Therefore, in the present study, the kinetic of diacetyl formation and reduction was investigated. The influence of such parameters as adjunct rate, pitching rate, yeast reuse, temperature, dissolved oxygen and pH were also studied in details. The results showed that primary fermentation temperature and pitching rate played the most important roles in both the formation and reduction of diacetyl. Along with Maturex enzyme, they were chosen as the critical parameters for further optimization in order to shorten the maturation time. The design of experiments for the optimization was done using Doehlert matrix and Nemrod software with three objective criteria namely low diacetyl content, desirable alcohol content and low primary fermentation time. The optimum Maturex enzyme needed to use is 0.01 - 0.02 g/1, corresponding to the temperature range of 11 to 13°C and pitching rate of 15 million cells /ml. In order to examine the suitability of the model after optimization as well as its applicability, a pilot scale was carried out at the fermentation capacity of 5000 liters/ tank. With the aim of saving enzyme cost, only 0.01 g/1 Maturex enzyme was used. Other fermentation conditions were 13°C for primary fermentation temperature and 15 million cells/ ml for pitching rate. It was seen that there was no significant difference between the pilot and the control sample in terms of both beer characteristics and sensory evaluation and the desired results were obtained. Moreover, economic calculations showed that 625 USD will be saved per day if the application of Maturex enzyme is done under the suggested optimization conditions as compared to those being used at present. Therefore, it can be concluded that adding Maturex is completely considered as a feasible and acceptable solution for cutting down the maturation time in brewing process. The study on continuous maturation method using immobilized yeast was divided into two main steps. In order to find the best heat treatment, a first step in continuous maturation process, different heating temperature and time combinations were investigated. It was then found that the conversion of α- acetolactate to diacetyl was good when this was at 60°C for 35 minutes. The next step was diacetyl reduction by using immobilized yeast reactor. Gel beads were formed by dropping the mixture of 109 cells/ml yeast concentration and 2% sodium alginate into 1% CaCl2 solution. Based on the bead characteristics, the diameter of 2mm was found the most suitable for the continuous maturation process. Besides, the effect of different column temperatures was also studied. It was showed that at each temperature, a particular residence time was required. If the maturation was kept two long, the increase in diacetyl content was observed. The effect of continuous maturation to the quality of finished beer was then examined based on gas chromatography analysis of the flavor compounds in the final beer product. A conclusion of the study is that the best maturation process should be conducted at 2°C for 3 hours residence time in the immobilized column. The two methods used for reducing maturation time have great potential to be used in industrial scale. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. FB-04-01 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Food Engineering and Bioprocess Technology (FB) |
| Chairperson(s) | Rakshit, Sudip Kumar; |
| Examination Committee(s) | Jindal, Vinod K.;Athapol Noomhorm; |
| Scholarship Donor(s) | Government of Netherlands; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2004 |