Yeast is the magical ingredient that transforms a dense ball of flour and water into a light, airy loaf of bread. This tiny single-celled fungus has been helping humans bake bread for thousands of years, and understanding how it works is fundamental to successful bread making. Whether you're troubleshooting flat loaves or simply want to deepen your baking knowledge, this guide explores everything you need to know about yeast.
What Yeast Does in Bread
At its core, yeast's role in bread making is simple: it produces carbon dioxide gas and alcohol through a process called fermentation. When yeast consumes sugars (either added sugar or sugars naturally present in flour), it releases CO2 as a byproduct. This gas gets trapped in the gluten network created by kneading, causing the dough to expand and rise.
But yeast does more than just create gas. The fermentation process also develops flavour compounds that give bread its characteristic taste and aroma. Bread made with longer fermentation times develops more complex flavours than quick-rise loaves—one reason why artisan bread often tastes different from supermarket loaves despite similar ingredients.
The alcohol produced during fermentation evaporates during baking, but it too contributes to flavour development and helps with the browning process that creates appetising crusts.
Types of Yeast Available in Australia
Instant Yeast (Bread Machine Yeast)
This is the preferred yeast for bread makers. Instant yeast consists of smaller granules that dissolve quickly and don't require activation in warm water before use. Simply add it directly to your dry ingredients. It's sometimes labelled as "bread machine yeast," "rapid-rise yeast," or "quick yeast."
Popular Australian brands include Lowan and Tandaco. You'll find it in the baking aisle of most supermarkets, typically sold in sachets or small jars. Once opened, store in an airtight container in the refrigerator.
When adding instant yeast to your bread maker, create a small well in the flour and place the yeast there, keeping it away from direct contact with liquid until mixing begins. This ensures the yeast activates at the right time.
Active Dry Yeast
Active dry yeast has larger granules than instant yeast and traditionally requires "proofing"—dissolving in warm water with a pinch of sugar for 5-10 minutes until it becomes foamy. This step activates the yeast before adding it to the dough.
While some older bread maker recipes call for active dry yeast, most modern machines work better with instant yeast. If you only have active dry yeast available, you can use it in bread makers, but consider proofing it first in a small amount of the recipe's liquid, or expect slightly longer rising times.
Fresh Yeast (Compressed Yeast)
Fresh yeast comes as a moist, crumbly block and is highly perishable, lasting only about two weeks refrigerated. It's rarely used in home bread machines due to its short shelf life and measurement challenges. Professional bakers prize it for its reliable performance, but for home use, instant yeast is more practical.
If a recipe calls for fresh yeast and you have instant yeast, use approximately one-third the amount specified. For example, substitute 7g instant yeast for 20g fresh yeast.
Sourdough Starter
While not technically commercial yeast, sourdough starter is a natural leavening agent containing wild yeast and beneficial bacteria. Some bread makers have sourdough programs that work with starter cultures, though results vary. Traditional sourdough requires longer fermentation times than most bread maker cycles allow.
What Yeast Needs to Thrive
Understanding yeast's requirements helps you create optimal conditions for successful rising:
Food (Sugar)
Yeast feeds on sugars. While flour contains enough natural sugars for basic bread, added sugar accelerates fermentation and produces more gas. Too much sugar, however, can actually inhibit yeast by drawing moisture away from the cells through osmosis. Sweet bread recipes often use more yeast to compensate.
Moisture
Yeast requires moisture to become active. In bread making, the liquid ingredients provide this. Proper hydration is crucial—too little moisture and yeast activity is sluggish; too much and the dough becomes slack and rises poorly.
Warmth
Yeast is most active between 25-38°C. Below this range, activity slows significantly. Above 45°C, yeast begins to die. Water temperature is particularly critical—aim for 35-40°C (lukewarm, comfortable to touch). Your bread maker controls temperature during rising, but starting with appropriate ingredient temperatures helps.
Test water temperature by touch: it should feel pleasantly warm but not hot. If it's uncomfortable to hold your finger in, it's too hot and will damage or kill the yeast.
Time
Yeast needs time to produce enough gas for proper rising. Bread maker cycles are designed to provide adequate fermentation time, but factors like ambient temperature and ingredient temperatures can affect timing. Rapid bake cycles produce acceptable bread but with less flavour development than standard cycles.
What Kills or Inhibits Yeast
Heat
Temperatures above 50°C kill yeast rapidly. Never use hot water in bread recipes—even if it feels okay to you, it may be lethal to yeast. Microwaved water often has hot spots that can damage yeast even if the overall temperature seems fine.
Salt
Salt controls yeast activity and is essential for flavour and gluten strength. However, direct contact between salt and yeast can inhibit or kill the yeast cells. When adding ingredients to your bread maker, keep salt and yeast separated—typically salt goes with dry ingredients while yeast sits atop the flour, away from liquid.
Old Age
Yeast is a living organism that dies over time. Check expiration dates before using, and discard yeast that's past its prime. Even yeast stored correctly loses potency as it ages.
Improper Storage
Exposure to air, moisture, and heat degrades yeast quality. Once opened, transfer yeast to an airtight container and refrigerate. Frozen yeast lasts even longer—up to several years—though it should be brought to room temperature before use.
Testing Yeast Freshness
If you're unsure whether your yeast is still active, perform this simple test before committing to a full recipe:
- Dissolve 1 teaspoon of sugar in 1/4 cup of warm water (around 40°C)
- Sprinkle 1 teaspoon of yeast over the surface
- Wait 10 minutes
Active yeast will foam and bubble, often doubling in volume. If nothing happens, the yeast is dead—discard it and purchase fresh yeast before baking.
Yeast Quantities and Adjustments
Most bread maker recipes specify exact yeast quantities, and precision matters. Too little yeast results in dense bread that doesn't rise properly. Too much yeast causes over-rising followed by collapse, plus an unpleasant yeasty flavour.
Adjustments may be needed in certain situations:
- Hot weather: Reduce yeast by about 1/4 teaspoon and use cooler water. High ambient temperatures accelerate fermentation.
- Altitude: If you live at significant altitude (above 1000m), reduce yeast slightly as lower air pressure allows faster rising.
- Whole grain flours: Heavier flours may benefit from slightly more yeast to achieve adequate rise.
- Sweet doughs: High-sugar recipes often need more yeast since sugar competes for moisture and can slow yeast activity.
Never add extra yeast thinking it will guarantee a higher rise. Excess yeast causes bread to rise too quickly, exhaust its food supply, and then collapse. Trust your recipe quantities and adjust only when troubleshooting specific problems.
Yeast-Free Alternatives
While yeast is the traditional leavening for bread, alternatives exist for those who can't use it:
Baking powder and baking soda: These chemical leaveners produce quick breads and soda breads. They work immediately and don't require rising time, but produce bread with different texture and flavour than yeast bread. Many bread makers have quick bread or cake programs suitable for these recipes.
Sourdough starter: Wild yeast captured and maintained in a sourdough starter provides natural leavening with distinctive tangy flavour. Requires more hands-on time than commercial yeast.
Understanding yeast transforms you from a recipe follower to a bread maker who can troubleshoot problems, adjust for conditions, and consistently produce beautiful loaves. This microscopic fungus is your essential partner in bread making—treat it well, and it will reward you with countless delicious loaves.