An Environment That Promotes Yeast Growth
Certain environmental factors, such as oxygen or temperature, control yeast growth. Changes in each parameter can either promote or inhibit yeast activity. That is why it is essential to maintain them under optimal conditions.
Temperature Tolerance of Different Types of Yeast
The temperature of the environment in which the yeast is found directly influences the activity and multiplication of its cells. The optimal temperature for their growth depends on the strain from which they originate. There are yeasts:
- psychrophiles, which thrive in cold conditions;
- mesophiles, which thrive at moderate temperatures;
- and thermophiles, which require high temperatures to survive.
Most yeasts, such as baker’s yeast, are mesophilic 1. Here’s how it behaves at different temperatures.
- Between 0 and 5°C, baker’s yeast shows little or no activity.
- Between 20 and 25°C, it grows rapidly.
- Bread fermentation generally takes place between 25°C and 32°C. This is the ideal temperature range for baker’s yeast growth.
- Between 30 and 35°C, it still exhibits a high level of activity and ferments.
- Above 40°C, the activity of its cells is inhibited.
- At 52°C and above, its cells are destroyed 2.
Good to know: Can baker’s yeast be frozen?
Different strains of yeast have varying degrees of resistance to freezing. Fresh baker’s yeast and instant dry yeast can be frozen for a few months, provided they are sealed in an airtight container. Note that the yeast cells will deteriorate over time.
pH Level and the Presence of Oxygen
pH, or hydrogen ion concentration, measures the degree of acidity or alkalinity of a substance. The pH level of the environment directly influences yeast activity.
- A pH below 4 (very acidic) can inhibit yeast activity.
- A pH between 4 and 6 (slightly acidic) is ideal for fermentation.
- A pH above 6 (more alkaline) promotes the presence and growth of bacteria that will compete with the yeast.
The availability of oxygen also affects yeast activity and growth stages. In the aerobic phase (in the presence of oxygen), the cells consume sugar and multiply. In the anaerobic phase (with little or no oxygen), this microorganism converts sugar into ethanol (alcohol) and carbon dioxide. It is this phase that enables, for example, the production of alcoholic beverages such as beer and wine.
What nutrients does yeast need?
Yeast cells require certain nutrients, such as sugar, to maintain their activity. The concentration of these nutrients in the culture medium will change during the production process.
Essential Nutrients
The growth of yeast cells and their ability to ferment are directly linked to the nutrient sources from which they draw sustenance. A balanced diet is essential for these microorganisms to perform at their best.
Yeast feeds primarily on sugar sources (glucose, fructose, sucrose) found in various fermentation media such as cane or beet molasses, flour, and so on. It also requires nitrogen sources to synthesize proteins, which it converts into aromatic compounds during bread fermentation. Other nutrients, such as minerals (magnesium, zinc) and vitamins (biotin), also play a role in yeast metabolism.
Resourceful yeast manufacturers have capitalized on yeast’s natural need for selenium to produce yeast enriched with highly bioavailable selenium. Indeed, yeast has the ability to convert inorganic selenium into organic compounds, notably selenomethionine (SeMet) and selenocysteine (SeCys). These organic compounds have superior bioavailability, which explains the widespread use of selenium-enriched yeast in the development of dietary supplements, functional foods, and health products.
Nutritional Supplements for the Brewing Industry
Brewers can add a mixture of nutrients to their yeast during the brewing process to enhance its performance. Nutrient requirements vary between top-fermenting and bottom-fermenting yeasts, as well as from one strain to another. They also depend on the composition of the wort, the water, the temperature, the volume of beer brewed, and other factors. Supplements added during brewing may consist of nitrogen, vitamins, and minerals such as calcium, phosphorus, potassium, magnesium, zinc, and manganese.
Did you know that brewers and winemakers use yeast derivatives (inactive yeast, yeast hulls, yeast extracts) to optimize the yeast growth phase in the wort and reduce the risk of slow or stalled fermentation?
Yeast Management: Best Practices
Once the yeast has been produced, following best management practices helps preserve its ability to multiply and ferment.
Inoculation and Storage
Yeast subculturing is a technique that involves harvesting cells from an existing culture and transferring them to a new, controlled culture medium to promote further growth. Subculturing increases the yeast yield and helps maintain a pure, active culture.
Yeast storage conditions also affect the viability of the cells. The temperature and humidity levels of the environment must be appropriate for the type of packaging. It is also important to adhere to the recommended shelf life and prevent contaminants from compromising these microorganisms during storage.
Preventing the Risk of Contamination
Yeast cultures can be contaminated by various sources. Contaminants may originate from the environment, the people handling them, equipment, water, and more. They can include bacteria, molds, other yeast strains, and even chemicals. Regular cleaning and quality control measures are implemented to prevent contamination during the production process.
The Role of Genetic Factors in Yeast Growth
The strains currently marketed by yeast manufacturers have been developed for their growth potential and for the performance they deliver in their end applications. Their genetic profile allows them, for example, to withstand variations in temperature and pH, as well as increased alcohol concentrations…
In short, yeast cell proliferation depends on many factors: the right temperature, an appropriate pH, sufficient nutrients… When all these conditions are met, this microorganism works efficiently, whether it’s to make bread rise, ferment beer, or produce ethanol…
