Yeast is an incredible beast with an unparalleled ability to make bread rise yet an intimidating reputation.
But with a little attention and practice this single-cell power house will have you pulling out satisfyingly-risen loaves out of the oven, time after time.
Not only does this culinary wonder leaven dough but it provides flavour and aroma and contributes to your bread’s nutritional value.
The science of yeast
Yeast has been used by man to make alcohol and bread for thousands of years. It’s everywhere - every time you touch anything, you probably are picking up and putting down yeast. The official name for the yeast that bakers use is Saccharomyces cerevisiae or ‘sugar-eating fungus’. This live organism needs food, warmth, and moisture to thrive and it has a phenomenal growth rate, duplicating itself by a process called budding. Yeast feeds on sugar derived from flour when it is hydrated which it converts into alcohol and carbon dioxide. This gas is the rising agent and expands the dough as it is trapped within the dough’s protein matrix. The by-products of fermentation create the subtle flavours and texture that make a great loaf. The yeast continues to grow and ferment until the dough reaches around 46C at which temperature yeast dies.
There’s only one way to get to know how yeast works: use it! Yeast is a good starting point for many bakers who are just beginning and want to leave making a sourdough starter until they are ready. It’s easy to get hold of, 2020 aside, convenient and cheap. But yeast can be daunting: it's alive, after all, and temperamental being sensitive to temperature, time, and other environmental factors. Getting to know this mysterious little organism is the first step to mastering it, and thereby getting more comfortable with baking bread in your own kitchen.
Yeast comes in three forms – fresh yeast, active dry yeast and instant yeast.
Developed in the mid-19th century, fresh yeast is the oldest commercial form of yeast. Each gram of compressed yeast contains roughly six billion active yeast cells so it packs a punch and will produce the most carbon dioxide of all the three types, giving your bread ample flavour. It’s sold in blocks of cake or compressed yeast that resemble crumbly, cream-colored modelling clay. It is highly perishable with a short shelf life of a few weeks and must be stored in the fridge in an airtight container. The challenges that come with fresh yeast eventually sparked the next wave of yeast innovation: dried yeast.
Active dried yeast
Dried yeast, one of the miracles of modern baking, was developed during the Second World War so soldiers could bake fresh bread in their camps. It’s a free-flowing granular powder made from millions upon millions of dehydrated single-celled organisms which are dormant. As the name suggests, active dry yeast must be ‘activated’ by dissolving the granules in some warm water from the recipe, according to the package directions. It is also perishable and, once opened, needs to be stored in an airtight container in the fridge. It tends to last longer than the date printed on the packet if it is kept in the refrigerator and will last longer in the freezer for up to a year. Just be sure to proof it first. When substituting for instant yeast, you will more as it is not as concentrated.
Instant dry yeast
This type of yeast describes any dry yeast that's ready for use the instant you open the package without adding water to it. It has a much smaller grain size than dry yeast and contains more live cells, making it rise much faster, meaning you can make bread with just one rise. Thanks to its unique manufacturing process, instant yeast is guaranteed to be 100% active and is far more reliable over time. Given instant yeast’s stability and shelf life, it’s a popular choice but it can lose out on flavour and strength compared to its fresh equivalent. Dry yeast is vulnerable to moisture, so keep it in airtight container where it will last months in the fridge and up to a year or so in the freezer.
How to proof yeast
To prevent baking failures of the unrisen kind, it is highly recommended that you proof your yeast before baking, to test whether it's still alive, able to start the fermentation process and eventually give rise to your bread. No special tests are needed, you just need to basically create a warm, moist environment in which yeast is typically prone to start working, and see whether it does or not.
Not all yeasts need proofing providing you’ve stuck to the shelf-life and storage recommendations. The two kinds of yeast you may want to test are active dry yeast and fresh yeast.
In a small bowl, mix together 1/4 cup lukewarm water (or milk), 1/2 teaspoon sugar and 1 teaspoon instant yeast. Let it stand for 5-10 minutes (you may need to leave it longer on cold days) if it starts to foam and bubble and produce a yeasty aroma, it’s active. Be careful not to use hot water as this will kill the yeast.
Active dry yeast needs the liquid to be ideally around 110°F while fresh yeast needs only 95°F to react. Remember to take off 1/4 cup of water, or whatever amount you used for proofing/dissolving, from the recipe.
Adding sugar to fresh yeast makes it easier to mix into the water and encourages it to ferment. Simply:
- Mash the yeast and sugar in a bowl using the back of a spoon until the yeast starts to dissolve.
- After about a few minutes, the crumbly yeast will turn into a smooth liquid.
- Add water, following your recipe.
For active dry yeast you don’t necessarily have to add sugar but it kickstarts the fermentation and increases the yeast’s activity. This is particularly useful when you are trying to revive the yeast from the freezer.
We often use a teaspoon of sugar to get the yeast going unless we are following a particular recipe for a slow-rising loaf with added flavour.
Do you need an autolyse stage when using commercial yeast?
Strictly speaking no, but Risen recommends an autolyse for proper dough development. An autolyse can be added to almost any bread recipe as it is simply a short rest after combining flour and water, allowing the flour to fully hydrate and the dough to become more extensible. Salt and yeast tighten gluten, working against the development of extensibility which is why we omit them from the autolyse.
By delaying the addition of yeast, a sourdough starter and salt, you have a better chance of easier shaping, greater loaf volume and a more open crumb structure.
To add instant, dry yeast and/or a stiff sourdough starter after an autolyse, dissolve them in a small amount of water reserved from the autolyse. Mix gently until the ingredients are fully incorporated before beginning to knead.
If your recipe requires a significant amount of spelt flour, which is known to typically be very extensible, you can skip the autolyse and just mix the yeast in at the beginning.
Before starting to mix, check that all your ingredients you put into the dough are at room temperature. If you adding in milk, eggs, or butter, for brioche bread for example, that are straight from the fridge it will drop the temperature of the dough.
The role of fermentation
Fermentation is truly the core of making bread and it happens as soon as yeast comes into contact with flour and water. Alcoholic fermentation produces carbon dioxide gas which gets trapped in the gluten structure. As the yeast continues to respire, more gas is produced, filling the pockets throughout the bread and forcing them to expand. The ability to correctly ferment the dough without under or over-fermenting is a challenge that many beginner bakers struggle with and it does take practice. Generally speaking, more fermentation means tastier bread.
Fermentation happens in four stages -
Also referred to as bulk fermentation and the first proof, is the dough’s first resting period after yeast has been added, before shaping. It’s one of the most important steps of yeast bread baking as the yeast does most of it work of consuming sugars to produce carbon dioxide gas bubbles during this stage. It is called bulk because even if you plan to make multiple loaves, the dough ferments in one, single mass. Don’t rush this bit: total bulk fermentation is usually 1.5 to 2.5 hours at room temperature. Cutting bulk fermentation short might mean your dough won't be fermented enough and you'll have under-proofed dough on your hands.
For sourdough, a series of gentle folding happens during bulk fermentation to help develop the gluten structure and move around the yeast and sugars. It also helps regulate dough temperature meaning no cold or warm parts at the top or bottom. Yeast likes to be kept cosy! Start folding around 30 minutes into the bulk rise and then every half an hour.
For more info on the stretch and fold technique, head over to our School of Baking techniques pages.
This is often divided into three steps: pre-shaping, bench rest and final shape. Fermentation is still occurring at this stage but you are moulding all that gluten and air into a desired shape. While pre-shaping is not strictly necessary, it gives you the opportunity to check in with your dough, to assess its strength and fermentation activity. The dough should be pillowy and a little springy now, thanks to the yeast and its carbon dioxide output. Shaping is your last chance at manipulating the dough so be firm.
For more info on shaping techniques, head over to Techniques
Proofing, also called the second rise, is a continuation of the fermentation process. Proofing can refer to any stage of fermentation, but is especially associated with the final rise that happens after dough is shaped, just before baking. Yeasted doughs need to undergo a final proof after shaping to regain volume and extensibility before being baked. During final proofing, acids are formed through yeast activity and contribute to flavour development.
Proofing temperature affects flavour. Depending on time available, you can use the fridge for this final fermentation stage. As the temperature reaches zero, the carbon dioxide production rate slows down and halts, creating a more intense and sweeter tasting bread. This is known as retarding.
The yeast’s activity will continue in the oven which is visible as oven spring. This is where the yeast feeds on the remaining sugars rapidly in the warmth of the oven until it gets too warm or the crust sets. At this point the bread can no longer rise. When the oven temperature reaches 68C (155F) the yeast cells die, bringing yeast fermentation to an end.
Why yeasted dough needs two rises
Although much of the changes needed for leavened bread take place during the knead and first rise, a second rise allows yeast more time to work, helping to develop a lighter, chewier texture, with an even crumb and a more complex flavour.
During the first rise, gas fills the dough and these bubbles actually separate the yeast from its food supply. But the yeast needs to continue to work and a popular way of doing this is to gently punch or knock the gas out of the way. Now the yeast has been reunited with the food supply and can continue to improve texture and flavour by creating gas, hence a second rise. To maximise the characteristics of the bread, the yeast needs this extra time to work.
Why yeast can fail
The most common reason yeast fails is that the water is too hot. Yeast is a living organism, and it will die if it gets too hot. To test your liquid, put a drop on the inside of your wrist. If it feels hot, the liquid is probably too warm for the yeast. It’s better for the liquid to be too cold than too warm. If the liquid is cold, your dough will rise more slowly, but it will rise as the kneading process creates friction, and therefore heat, to activate the yeast anyway.
A less common reason yeast fails is the yeast is too old. Yeast is a microorganism and does have a definite life span. For best results, always make sure to use yeast before the “best by” date and to be sure to proof the yeast before adding it.
Adding salt directly onto the yeast can inhibit or even kill it in extreme cases. To prevent salt from foiling your bread bakes, measure carefully and add your yeast and salt on opposite sides of the mixing bowl.
Where to get it
Fresh yeast can be found in most supermarkets, in the fridge section, depending on the size of the store. You may be able to buy fresh yeast from your local bakery or even the bakery counters of supermarkets, if they bake their bread in store. It’s worth asking! Health food shops also stock most varieties of yeast. Active dry yeast and instant yeast are more readily available and can be found in the home baking aisle of supermarkets. And, of course, there is always online.