The success of ethanol production relies, partly, on various factors that can affect fermentation, with temperature playing a pivotal role. Yeast performance in converting feedstocks to ethanol is strongly linked to fermentation temperature, as it can only satisfy its needs under a suitable temperature environment.
In this article, we will explore the effects of temperature on ethanol production, dissecting its impact on yeast and growth, glucoamylase activity, ethanol fermentation, and strategies to control and counteract temperature-related challenges.
The impact of temperature on yeast growth
Temperature during rehydration has a strong influence on yeast activity during ethanol production. Optimal temperature for yeast rehydration is around 35°C +/-5°C (95°F +/-41°F), and 30-32°C (86-89°F) for yeast growth. In case of lower temperature control, yeast activity is lowered, and bacteria or wild yeast may take advantage of this non-favorable environment for yeast. On the other hand, higher temperatures will favor premature yeast ageing and faster bacteria growth, as well as undesirable byproducts. Maintaining the right temperature is crucial to ensure yeast functions optimally and can then convert sugars efficiently into ethanol.
The effect of temperature on glucoamylase
Temperature directly affects glucoamylase, and out-of-range temperatures can either slow down or denature enzymatic activity. In the case of simultaneous saccharification and fermentation (SSF) processes, lower fermentation temperatures will inhibit enzyme activity, resulting in insufficient sugar breakdown. This directly affects productivity, as fermentation cycles’ length increases. However, saccharification increases with temperature and can quickly increase osmotic pressure within the fermenter, affecting yeast growth. It is essential to strike a balance between the temperatures required for glucoamylase and yeast to perform optimally.
Temperature's consequence on yeast fermentation
The fermentation process itself is highly temperature sensitive. Ethanol production occurs most efficiently within 30°C to 34°C. Within this range, the higher the temperature the faster the ethanol production. When temperature exceeds 34°C, ethanol productivity starts to decrease while glycerol production increases. High temperatures also increase ethanol toxicity, having a cumulative effect on yeast inhibition.
Selecting a yeast with strong tolerance to higher temperatures is essential to optimize fermentation performance.
Strategies for controlling fermentation temperature
While the optimal temperature for yeast rehydration and growth varies from the optimal temperature for ethanol fermentation, it still needs to be kept as stable as possible during the entire process. Managing fermentation processes gets more difficult at higher ambient temperatures. However, various parameters can still be optimized to control temperatures of the entire fermentation process within a reasonable range:
- Constant temperature monitoring to spot critical changes in a timely manner,
- Implementing appropriate cooling equipment to maintain optimal temperature,
- Maintaining cooling tower efficiency and ensuring it is in good operating condition,
- Timely adjusting the amount of nitrogen supplementation during fermentation to limit the metabolic heat production of yeast,
- Choosing a highly resistant yeast strain, able to accommodate higher temperatures.
Understanding and managing temperature factors is key to produce ethanol sustainably and efficiently. While being a limiting factor, temperature can also be directly controlled. It plays a critical role in the production process, affecting yeast rehydration, growth, glucoamylase activity, and fermentation itself. Implementing temperature control strategies will help in counteracting the adverse effects of temperature variations, ensuring consistent and efficient ethanol production.