Sign up to access the complete lesson and track your progress!
Unlock This CourseYeast is one of the most important microorganisms in food production. These tiny living cells have been helping humans make food and drinks for thousands of years, even before we understood how they worked. From the bread on your breakfast table to the fizzy drinks you enjoy, yeast plays a crucial role in creating many of our favourite foods.
Key Definitions:
Yeast belongs to the kingdom of fungi, just like mushrooms, but it's much smaller - you need a microscope to see individual yeast cells. The most common type used in food production is Saccharomyces cerevisiae, also known as baker's yeast or brewer's yeast. These microscopic workers are alive and need food, warmth and moisture to survive and reproduce.
Yeast is like a tiny factory that converts sugar into useful products. When yeast cells feed on sugars, they produce two main waste products that are incredibly valuable to us: carbon dioxide gas and ethanol (alcohol). This process is called fermentation and it happens when there's little or no oxygen available.
The magic of fermentation follows a simple chemical equation: Sugar + Yeast → Carbon Dioxide + Alcohol + Energy. But what's really happening inside those tiny yeast cells is quite remarkable. Yeast contains special enzymes that break down complex sugars into simpler ones, then convert them into the products we want.
Yeast feeds on various sugars including glucose, fructose and sucrose. In bread making, enzymes in flour convert starch to sugar for the yeast to eat.
The CO₂ gas produced creates bubbles that make bread rise and gives fizzy drinks their sparkle. This is why bread has a spongy texture.
Ethanol is produced alongside CO₂. In bread making, this evaporates during baking, but in brewing, it's the main product we want.
Bread making is probably the most familiar use of yeast in food production. When you mix yeast with flour, water and a bit of sugar, you're creating the perfect environment for fermentation to begin. The yeast feeds on sugars in the flour and produces carbon dioxide gas, which gets trapped in the stretchy gluten network of the dough.
A typical bread recipe uses about 7g of dried yeast for 500g of flour. The yeast needs warmth (around 25-30°C), moisture from the water and food from the flour's sugars. During the rising process, which takes 1-2 hours, the yeast doubles the dough's size by producing thousands of tiny CO₂ bubbles. When baked at 200°C, the alcohol evaporates and the bubbles set, creating the bread's characteristic texture.
Yeast is quite fussy about its living conditions. Too hot and it dies; too cold and it works very slowly. The ideal temperature for bread making is around 25-30°C - about the same as a warm room. The yeast also needs moisture to stay active and sugar to feed on.
Below 5°C, yeast becomes dormant. Above 50°C, it starts to die. Professional bakers carefully control temperature to get consistent results. This is why recipes often mention using lukewarm water.
The alcohol industry relies heavily on yeast fermentation to produce beer, wine and spirits. Unlike bread making, where we want the carbon dioxide and discard the alcohol, brewing focuses on capturing the alcohol while sometimes keeping the CO₂ for fizzy drinks.
Beer making starts with malted barley, where enzymes convert starches into sugars. Yeast is then added to ferment these sugars into alcohol and CO₂. Different types of yeast produce different flavours - ale yeasts work at warmer temperatures and create fruity flavours, while lager yeasts prefer cooler conditions and produce cleaner tastes.
Barley grains are soaked and allowed to start growing, then dried. This activates enzymes that convert starch to sugar.
The malted barley is mixed with hot water to extract the sugars, creating a sweet liquid called wort.
Yeast is added to the wort and fermentation begins, typically lasting 1-2 weeks depending on the beer style.
The yeast you buy in shops doesn't just appear - it's grown in huge industrial facilities under carefully controlled conditions. Commercial yeast production is a fascinating process that involves growing billions of yeast cells in large fermentation tanks.
Companies like Lesaffre and Angel Yeast produce millions of tonnes of yeast annually. They start with a pure yeast culture and grow it in stages, from test tubes to massive 100,000-litre tanks. The yeast is fed on molasses (a sugar-rich byproduct of sugar production) and given optimal conditions to multiply rapidly. A single yeast cell can produce 20 billion descendants in just 10 hours under perfect conditions!
Different forms of yeast suit different purposes. Fresh yeast is alive but perishable, dried yeast has longer shelf life but needs reactivating and instant yeast can be mixed directly into flour.
Fresh yeast must be refrigerated and used within weeks. Dried yeast can last months at room temperature. Proper storage prevents contamination and maintains yeast viability.
Understanding what makes yeast happy is crucial for successful food production. Several environmental factors can speed up, slow down, or completely stop yeast activity.
Temperature is the most critical factor - yeast works fastest at around 30°C but can survive much cooler temperatures. pH levels matter too; yeast prefers slightly acidic conditions around pH 4-6. Salt concentration affects yeast activity, which is why bread recipes balance salt carefully.
Cold slows fermentation (useful for slow-rise breads), while heat speeds it up but can kill yeast if too hot.
Yeast needs sugar to survive, but too much sugar can actually inhibit its growth through osmotic pressure.
Yeast can work with or without oxygen, but produces different products - alcohol without oxygen, just CO₂ with oxygen.
Today's food industry continues to find new ways to use yeast. Beyond traditional bread and beer, yeast is used to produce vitamins, flavour enhancers and even alternative proteins. Scientists are developing new yeast strains that work faster, tolerate extreme conditions, or produce specific flavours.
Genetic engineering is creating 'designer yeasts' that can produce specific compounds. Some modified yeasts now make vanilla flavouring, others produce omega-3 fatty acids and researchers are working on yeasts that could help create sustainable meat alternatives. The global yeast market is worth over £3 billion annually and continues growing.