**Abstract**

Fermentation technology is still being developed in all aspects, with the aim of improving the yields and qualities of products and reducing the costs of production. Increasing the yields of fermentation products can be accomplished by optimizing the factors that influence the process, including both the microbe itself and the environment. For example, the acetic acid production process from raw materials can be performed simultaneously with submerged batch fermentation using mixed cultures of anaerobic and facultative anaerobic *S. cerevisiae* and obligate aerobic *A. aceti*. This system is very simple because it only has one stage. In this system, efforts can be made to enhance the yields of acetic acid production, including evaluating the availability of nutrients in the medium and determining the optimum proportion of microbial abundance and agitation speed. Under optimal conditions, the resulting increases in acetic acid yields occur with high conversion efficiency. These results can then be applied on an industrial scale by integrating these findings with advanced technologies in the operating system.

**Keywords:** acetic acid production, *Acetobacter aceti*, aerobic submerged fermentation, mixed culture, *Saccharomyces cerevisiae*

## **1. Introduction**

The fermentation industry has developed rapidly, especially as bioreactors have become the center of the process, as previously described [1]. The factors that have been the focus of development include the feeding of the bioreactor (batch, fedbatch, and continuous mode of operation), the use of microbial cultures (single strain or mixed culture processes), the availability of oxygen (aerobic, microaerobic, and anaerobic processes), and the mixing of the bioreactor during the process, particularly in the production of acetic acid. Acetic acid is produced from alcohol, and alcohol is produced from sugar. These two processes require different types of microorganisms. The microorganisms most commonly used in the fermentation of alcohol are yeasts, such as *Saccharomyces cerevisiae*, and bacteria, such as *Zymomonas mobilis*. However, for industrial fermentation, *Z. mobilis* appears to be inferior to *S. cerevisiae*, due to the reduced biomass production of the bacterium when pH decreases [2]. Commonly used acetic acid bacteria (AAB) include *Acetobacter* and *Gluconacetobacter*, two AAB genera that oxidize ethanol more easily than sugars [3], and exhibit resistance to high acetic acid concentrations and low pH [4]. For largescale industries, the efficiency of the fermentation process design and operation continues to be developed, with the aim of improving the yields and qualities of the products and reducing the costs of production.
