Temperature plays a central role in yeast behavior. As we’ll see, it influences the activity of enzymes present in the yeast cell and directly affects the biological mechanisms that allow this microorganism to convert sugars.
Understanding Yeast Metabolism
Yeast metabolism refers to the set of biological mechanisms that enable this microscopic organism to survive, multiply, and produce energy. Specifically, yeast cells use glucose and other sugars as a fuel source to sustain their vital functions. When this single-celled microorganism comes into contact with these nutrients, the yeast triggers a series of biochemical reactions.
Yeast cells are unique in that they can live with or without oxygen and operate via two metabolic pathways1.
Aerobic respiration, which uses oxygen.
In the presence of oxygen, yeast can respire and efficiently produce energy, which it uses to maintain its functions and multiply rapidly. During this phase, sugars such as glucose and fructose are converted into carbon dioxide and water. This process produces a large amount of energy.
It is this metabolic pathway that is utilized and optimized for industrial-scale yeast production. In breadmaking, aerobic respiration also comes into play at the very beginning of the bread-making process, during kneading. As oxygen gradually disappears from the dough, the yeast switches to fermentation.
Fermentation, without oxygen.
In the absence of oxygen, yeast favors a fermentative metabolism that converts sugars into carbon dioxide and alcohol, as well as other byproducts such as aldehydes, esters, and acids that give the final product its aromas.
During fermentation, yeast produces much less energy and multiplies only slightly. Yet it is yeast that enables the fermentation of wine, beer, bread dough, cherries, coffee, chocolate, and more…
At the heart of yeast metabolism are enzymes. These proteins are natural catalysts that facilitate reactions related to cell reproduction and fermentation. Their activity is controlled primarily by the expression of yeast genes and influenced by environmental factors. Temperature can significantly affect enzymatic activity.
The Role of Temperature in Yeast Activation
Temperature is one of the factors that influence the activity of yeast cells. When it varies, it activates or inhibits their various functions.
The optimal temperature range for yeast depends on the strain. Most yeast species are mesophilic: they prefer moderate temperatures and multiply optimally between 20 and 30°C2.
Baker’s yeast (Saccharomyces cerevisiae) has virtually no activity at low temperatures, below 5°C. As the temperature of its environment rises, its metabolic rate increases. For bread dough fermentation, the ideal temperature range is between 25°C and 32°C3. Above 40°C, certain cellular structures begin to break down and cell viability decreases. At the start of baking, the yeast continues to produce CO₂ until it reaches its inactivation temperature of around 50°C. And above 52°C, the yeast cells die.
How does temperature affect fermentation?
Temperature plays a major role in the fermentation process, whether in bread-making, winemaking, brewing, or even ethanol production. Temperature affects the rate of fermentation, alcohol formation, and the development of aromatic compounds.
Cold fermentation has different objectives than fermentation carried out at higher temperatures.
Cold Fermentation
Low-temperature fermentation methods aim to slow down the metabolic activity of yeast. They allow for better control of fermentation conditions and give the cells more time to develop the aromas that will be present in the final product.
Various cold fermentation methods are commonly used in baking. Bakers seek to slow down or halt the fermentation of bread dough by placing the dough pieces in a cold room or a controlled proofing chamber. The slow-rise method, for example, involves letting the dough rest for 24 hours in a cool environment, between 10 and 12°C, during the “second rise” stage—the second fermentation period in a bread recipe4.
Low-temperature fermentation is also used in brewing. Lagers, for example, are beers produced using bottom-fermentation methods, typically at a temperature between 10 and 12°C. The yeast strain specific to lager production operates at a cooler temperature than the strains used to brew other beers. Its fermentation process, which is slower, lasts several weeks. The fermentation conditions for lagers are temperature-controlled, using cooling systems. The goal is to prevent the heat produced by the fermenting cells from warming the mixture and developing undesirable flavors. When properly controlled, this bottom-fermentation technique produces more subtle, clean flavors centered on malt and hops5.
Higher-Temperature Fermentation
By using higher temperatures, hot fermentation generally aims to accelerate the fermentation process.
In baking, dough pieces can be placed in heated controlled-environment proofing chambers (up to 35°C) to reactivate or accelerate fermentation. Accelerated fermentation reduces the dough’s rising time. However, if not properly controlled, this method can negatively impact the bread’s flavor development and shelf life.
In brewing, top fermentation using a strain of Saccharomyces cerevisiae enables the production of ale-style beers. The fermentation time for these beers lasts only 3 to 8 days. The result is beers with a fruitier and spicier flavor profile than lagers.
Controlling Temperature Using Innovative Techniques
New materials, biosensors, smart systems… Recent technical innovations in fermentation control allow for very precise regulation of fermentation temperatures. For example, scientists have recently developed a multi-sensor array chip to monitor not only temperature but also pH, conductivity, dissolved oxygen, and glucose during yeast fermentation. This tool enables real-time monitoring of fermentation conditions without the need for sampling, allowing for immediate adjustment of parameters6.
Controlling fermentation temperature is a true science, and it is now possible to manage it with unparalleled precision. These technologies pave the way for increasingly well-controlled fermentation processes, resulting in high-quality products.
