**Author details**

Rubens Eliseu Nicula de Castro, Rita Maria de Brito Alves\*, Cláudio Augusto Oller do Nascimento and Reinaldo Giudici

\*Address all correspondence to: rmbalves@usp.br

USP – Universidade de São Paulo, São Paulo, Brazil

#### **References**


**4. Conclusion**

18 Fuel Ethanol Production from Sugarcane

**Acknowledgements**

**Author details**

**References**

A new era with a clean worldwide energy matrix is expected nowadays. Ethanol has been shown to be a fuel with great potential to meet this world's aspiration. In this new phase, the fuel needs to be recognized by its environmental benefits and not only by the energy that it contains. Consequently, it has to be rewarded according to the benefits it brings to the society. For this in recent years, the sugarcane industry has positioned itself not only as a food industry but also as an energy industry. Having a look into the sugarcane feedstock, bringing a different viewpoint, one could say that it produces three different kinds of energy: sugar—energy for human beings; ethanol—energy for transportation; and electricity—energy for a variety of uses. As an energy company, the process itself cannot be energetically wasteful. So, recent improvements in the process have aimed to maximize its efficiency; meaning that using less energy in the process itself results in more energy left to be sold as a product. However, many questions, such as the destination of the use of straw, bagasse, and vinasse, are still unanswered and will depend on the next technology improvement. This new era will result in increasing the demand for ethanol, which must be met not only by the increase in the production but also in the productivity and efficiency. Nevertheless, many technologies, with notorious performances, are not applied to the production of ethanol nowadays because of their low feasibility. They would become feasible, however, if ethanol was rewarded for its environmental benefits.

The authors kindly acknowledge FAPESP (Fundação de Amparo à Pesquisa do Estado de São

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Rubens Eliseu Nicula de Castro, Rita Maria de Brito Alves\*, Cláudio Augusto Oller do Nascimento and Reinaldo Giudici

\*Address all correspondence to: rmbalves@usp.br USP – Universidade de São Paulo, São Paulo, Brazil


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**Chapter 2**

Provisional chapter

**Clash of Kingdoms: How Do Bacterial Contaminants**

DOI: 10.5772/intechopen.78413

Brazilian fuel ethanol production from sugarcane is one of the largest industrial biotechnological processes in the world. However, in view of the complex chemical nature of this feedstock, as well as the non-aseptic conditions of the process, various stress conditions are imposed to the fermenting yeast. In this chapter, we deemed to elaborate a brief overview of the ethanol production process, and to dissect the chemical nature of sugarcane-based worts, as well as their physiological effects on the fermenting yeasts. Finally, the interplay between yeast and lactic acid bacteria, the two main players in the

Traditionally, ethanol production in Brazil has been coupled to sugar production. Sugarcane is initially pressed to separate the sugar-containing broth (sugarcane juice) from the fibrous solid residue (bagasse). Sucrose crystals are obtained by crystallization of the concentrated broth, and as a result a dark and viscous sucrose-rich residue (molasses) is obtained. Molasses is mixed with either water or sugarcane juice (sugarcane must) in different proportions and used for fermentation, normally in a fed-batch process with cell recycle (for an overview, please

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Clash of Kingdoms: How Do Bacterial Contaminants

**Thrive in and Interact with Yeasts during Ethanol**

Thrive in and Interact with Yeasts during Ethanol

**Production?**

Production?

Thiago Olitta Basso and

Thiago Olitta Basso and Felipe Senne de Oliveira Lino

Abstract

refer to [1]).

Felipe Senne de Oliveira Lino

http://dx.doi.org/10.5772/intechopen.78413

Additional information is available at the end of the chapter

ethanol fermentation process, is generally discussed.

1. Introduction to ethanol fermentation in Brazil

Keywords: ethanol, yeast, bacteria, chemical composition, stresses

Additional information is available at the end of the chapter

#### **Clash of Kingdoms: How Do Bacterial Contaminants Thrive in and Interact with Yeasts during Ethanol Production?** Clash of Kingdoms: How Do Bacterial Contaminants Thrive in and Interact with Yeasts during Ethanol Production?

DOI: 10.5772/intechopen.78413

Thiago Olitta Basso and Felipe Senne de Oliveira Lino Thiago Olitta Basso and Felipe Senne de Oliveira Lino

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.78413

#### Abstract

Brazilian fuel ethanol production from sugarcane is one of the largest industrial biotechnological processes in the world. However, in view of the complex chemical nature of this feedstock, as well as the non-aseptic conditions of the process, various stress conditions are imposed to the fermenting yeast. In this chapter, we deemed to elaborate a brief overview of the ethanol production process, and to dissect the chemical nature of sugarcane-based worts, as well as their physiological effects on the fermenting yeasts. Finally, the interplay between yeast and lactic acid bacteria, the two main players in the ethanol fermentation process, is generally discussed.

Keywords: ethanol, yeast, bacteria, chemical composition, stresses

#### 1. Introduction to ethanol fermentation in Brazil

Traditionally, ethanol production in Brazil has been coupled to sugar production. Sugarcane is initially pressed to separate the sugar-containing broth (sugarcane juice) from the fibrous solid residue (bagasse). Sucrose crystals are obtained by crystallization of the concentrated broth, and as a result a dark and viscous sucrose-rich residue (molasses) is obtained. Molasses is mixed with either water or sugarcane juice (sugarcane must) in different proportions and used for fermentation, normally in a fed-batch process with cell recycle (for an overview, please refer to [1]).

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In short, fermentation is initiated by the addition of the wort (also referred to as must), containing 18–25% (w/v) sugars, to a high-density yeast cell suspension, which represents 1/3 of the vat volume. Due to its large volumes, the feeding takes 4–6 h, and the fermentation is completed within 10 h. At the end of the fermentation, ethanol titres between 8 and 12% (v/v) are obtained, with a final cell density of 10–14% (w/v). Yeasts cells are then separated from the wine by centrifugation, which goes for distillation. The yeast slurry is diluted with equal volume of water and treated with sulfuric acid to reduce bacterial contamination, and reused in a subsequent fermentation cycle (Figure 1). This process configuration, using high cell densities and operating with cell recycling, is quite peculiar and allows two fermentation rounds per day during the harvest season that spans for almost 250 days. The reuse of cells reduces the need for yeast propagation, therefore diverting less sugar to yeast growth and saving it to ethanol formation.

2. Influence of wort composition on fermentation performance

As mentioned above, ethanol can be produced via direct fermentation of sugarcane juice, a mixture of juice and molasses, or molasses diluted in water [2, 3]. After shredding, cane is crushed in a milling tandem, constantly mixed with water, resulting in juices containing ca. 10– 15% sucrose content [3]. This process results in two types of juice: the primary – which leaves the first set of miller and is richer in nutrients – and the secondary – coming from the subsequent millers. The primary juice is commonly used for sugar production, whereas the

Clash of Kingdoms: How Do Bacterial Contaminants Thrive in and Interact with Yeasts during Ethanol Production?

http://dx.doi.org/10.5772/intechopen.78413

25

Sugarcane juice is passed through clarification (reducing impurities to less than 2%), decantation, and concentration (up to 18–25% total sugars) steps before sugar or ethanol production. These steps help reducing wild yeast and bacterial contaminations during the subsequent

During sugar production, the juice is clarified with lime, and concentrated through repetitive steps of evaporation and centrifugation. The concentrated juice later passes through a crystallization step, which catalyzes the formation of sucrose crystals that are later removed via centrifugation. The remaining sugar is left in the spent, dark and viscous liquid called molasses [4]. Molasses can be further recycled back into the sugar production process, resulting in several other types of molasses (i.e. A, B, C). The higher the number of recycles molasses is

Sugarcane juice and molasses are a complex mixture of carbohydrates, proteins, inorganic salts and organic acids [5], and wort prepared with either juice, molasses mixed with juice, or molasses diluted with water will have different nutrient composition, which will ultimately impact fermentation performance [1]. A comparison between sugarcane juice and molasses

Asparagine, glutamine and aspartic acid are the most abundant amino acids in sugarcanebased worts, while the disaccharide sucrose is by far the major sugar. Minor amounts of the monosaccharides, glucose and fructose, and the oligosaccharide, kestose, are also found [5]. Lipids are represented by a mixture of n-alkanes and ethyl and methyl esters of fatty acids (palmitate and oleate are the predominant), as well as of phytosterols (stigmasterol, β-sitos-

After fermentation cells are separated from the fermented wort (wine) by centrifugation, and this stream is sent for distillation. The distillation of ethanol generates a considerable amount

Vinasse is currently applied in soil as a fertilizer (fertirrigation), due to its high potassium titre [4, 9]. However, this high organic matter load shows deleterious impacts on soil, water and groundwater [10]. A possible solution to this environmental issue is the anaerobic digestion of vinasse, reducing the organic matter of vinasse for later fertirrigation use, and generating a

2.1. The chemical nature of sugarcane substrates and its by-products

secondary juice can either be used for sugar or ethanol production [3].

fermentation step, allowing for higher ethanol titre and yield [2].

subjected to, the poorer its quality as a fermentation substrate [2].

composition is shown below (Table 1).

of a wastewater stream named vinasse (stillage) [8].

new stream of revenue (biogas) for the sugarcane ethanol plant [11].

terol, and campesterol) [6, 7].

Figure 1. Simplified process flow diagram of the Brazilian ethanol production process (Courtesy of Jens C. F. Nielsen).
