Database results:
examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Yeast in Bread Production
Bread is one of the oldest and most widely consumed foods in the world. For thousands of years, humans have been making bread and yeast has played a crucial role in this process. But how exactly does this tiny microorganism transform a simple mixture of flour and water into a fluffy, delicious loaf?
Key Definitions:
Bread making is both an art and a science. The basic ingredients are simple: flour, water, salt and yeast. When mixed together, these ingredients begin a fascinating chemical and biological process. The yeast cells feed on sugars in the flour, producing carbon dioxide gas that gets trapped in the stretchy gluten network, causing the dough to rise.
Yeast is a living organism that belongs to the fungus kingdom. In bread making, we typically use Saccharomyces cerevisiae, also known as baker's yeast. These microscopic cells are powerful despite their size - just one gram of yeast contains billions of cells ready to get to work on your dough!
Fermentation is the heart of bread making. This biological process transforms a dense ball of dough into a light, airy loaf. Let's explore how it works:
When you mix yeast into dough, it immediately begins to feed on the sugars present in the flour. Through fermentation, yeast breaks down these sugars and produces two important by-products:
The CO₂ gas gets trapped in the elastic gluten network of the dough, creating thousands of tiny bubbles that make the dough expand and rise.
The alcohol produced evaporates during baking but contributes to the distinctive flavour and aroma of freshly baked bread.
Yeast also produces various organic compounds that give bread its complex, delicious flavour profile.
Not all yeast is the same! Bakers use different types depending on the bread they're making and the time they have available.
Also called cake or compressed yeast, this is living yeast sold in block form. It's moist, perishable and needs refrigeration. Professional bakers often prefer it for its reliable performance and rich flavour development.
Comes in two forms: active dry yeast (needs to be dissolved in warm water before use) and instant yeast (can be mixed directly with dry ingredients). Both are dormant yeast cells with much longer shelf life than fresh yeast.
Sourdough bread doesn't use commercial yeast at all! Instead, it relies on a 'starter' - a fermented mixture of flour and water containing wild yeasts and beneficial bacteria. Some bakeries maintain sourdough starters that are decades or even centuries old! The wild yeasts work more slowly than commercial yeast, which is why sourdough bread typically has a longer fermentation time (often 24 hours or more). This slow fermentation develops the distinctive tangy flavour and chewy texture that sourdough lovers crave.
Yeast is a living organism, so its activity is influenced by several environmental factors. Understanding these helps bakers control the bread-making process.
Yeast works best between 25-30°C. Too cold and it becomes sluggish; too hot (above 54°C) and it dies. This is why we use warm (not hot) water when activating yeast.
Yeast feeds on sugars, but too much sugar can actually slow down yeast activity through osmotic pressure. This is why very sweet doughs (like brioche) rise more slowly.
Salt controls yeast activity - it slows it down. Without salt, bread would rise too quickly and develop poor texture and flavour. However, too much salt can kill yeast cells.
Let's look at the typical steps involved in making a loaf of bread:
The distinctive holes in bread (called the "crumb structure") are actually the spaces where carbon dioxide bubbles from yeast fermentation were trapped in the dough! Different bread types have different crumb structures - from the large, irregular holes in ciabatta to the fine, even texture of sandwich bread.
While the basic principles remain the same, commercial bakeries use specialized techniques to produce bread on a large scale:
Developed in the UK in the 1960s, this process uses high-speed mixing, extra yeast and various additives to dramatically reduce fermentation time. It allows a loaf to be produced from flour to finished product in about 3.5 hours instead of the traditional 8-16 hours. Today, about 80% of UK bread is made using this method.
In contrast to industrial methods, many artisan bakeries are returning to slower fermentation techniques. These longer processes allow more time for flavour development and can make bread more digestible, as the extended fermentation breaks down more complex compounds in the flour.
Bread is more than just a tasty food - it provides important nutrients in our diet:
The fermentation process actually increases the nutritional value of bread in several ways. Yeast activity can increase the bioavailability of minerals by breaking down phytic acid (which can bind to minerals and prevent their absorption). Longer fermentation processes, like those used in sourdough bread making, can further enhance these effects.
For your IGCSE Biology exam, make sure you understand that yeast fermentation is an anaerobic process (occurring without oxygen) that produces carbon dioxide and ethanol. Be able to explain how this process causes bread to rise and how factors like temperature affect yeast activity.
Yeast plays a crucial role in bread production through the process of fermentation. This single-celled fungus transforms simple ingredients into one of our most beloved foods by producing carbon dioxide that makes dough rise. The activity of yeast is affected by various factors including temperature, sugar and salt content. Understanding these principles allows bakers to control the bread-making process and create different types of bread with varying flavours, textures and nutritional profiles.
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.