What is Active Dry Yeast?

Active dry yeast, also sometimes referred to as “baker’s yeast,” is a live culture used to make dough rise for breads, rolls, and some types of cake. It is known scientifically as Saccharomyces cerivisiae. Unlike wet yeasts, dry versions are dormant until warmed. Both feed on sugar, converting the glucose to carbon dioxide gas. The main advantage to purchasing yeast dry is its shelf life. It can last for a year or more in a cool, dark place, while wet versions must usually be used almost immediately. It is also viewed by many as simpler to use and measure.

The process through which sugar glucose is converted to carbon dioxide is essential to a great many baking projects. The gas bubbles cause the dough to expand, which allows air to penetrate and helps the loaf or roll bake evenly. The end result is often chewy and light rather than sticky and dense, as is often the result when yeast is left out or forgotten.

Active dry yeast looks like a finely granulated powder that “activates” in the presence of warm water or milk. Activation will usually happen naturally as a bread or roll bakes — the heat of the oven or fire is usually enough to trigger the sugar conversion, provided the dough is wet enough. Cooks will often “proof” the yeast in advance, though, which reduces the risk of yeast dying off or cooking too quickly.

Proofing usually starts when cooks set aside a small bowl of warm liquid and a pinch or two of sugar. Yeast is added, then the mixture is left to rest for anywhere from 10 to 15 minutes. If the yeast is fresh, the mixture will foam. If there are no bubbles or foam, something has gone wrong — the yeast may have expired, for instance, or the water may have been too hot. It’s very important that cooks not to overheat the water, which can kill the yeast. As a general rule, the water should be comfortably warm but not hot.

Proofing is not only a good way to test out a yeast’s strength, but it also saves a cook from wasting other ingredients to make a dough that will not rise. Once the foam appears, it is added to the other ingredients to form a dough, then left alone in a warm place, usually for about an hour. This "warm place" can be as simple as a sunny window ledge or a low-temperature oven — basically anywhere that is away from breezes and generally still. The dough will typically double in size during this time as the yeast interacts and activates, which is a good way to prepare it for the oven or fire.

For centuries, the most readily available form of yeast was fresh yeast, a product derived directly from natural fermentation. This sort of yeast was originally taken from food that was spoiling or decomposing. Scientific advances have given modern microbiologists new and improved ways of controlling yeast growth, and most of what is available for purchase today is created in controlled environments and is not related to decay at all.

Wet yeast is often the fastest to work with, and many cooking purists argue that it is the most authentic way to bake bread. It does have a limited shelf life, though. Consumers in most places can purchase it in blocks or small cubes, usually in the refrigerated section of a grocery store or bakery shop. Ever since active dry yeast was introduced to the mass market in the 1950s, it has typically been much more popular and readily accessible, even though using it can take a bit more time.

The Cincinnati, Ohio-based Fleischmann Company is credited with developing the first active dry yeast during the Second World War when it granulated wet yeast into tiny particles that were then dried and vacuum-sealed. According to popular lore, the product was created so that soldiers and troops could make fresh bread in their camps across Europe and the Pacific without having to worry about refrigeration or spoilage. The ease of use and simplicity of the product made it an instant hit in most world markets once the fighting ended.

Active dry yeast is typically sold in prepared packets, which makes measuring a snap. Many recipes are actually designed around this “packet” presentation, and will call for yeast based on how many packets are required rather than calling for a particular measurement. In most places, a packet contains roughly 0.25 ounces (7.3g) of yeast. This normally works out to be about 2.25 teaspoons.

Active dry yeast packets are typically printed with an expiration date, usually about a year forward from when they were produced. Yeast will often stay good past this date, but it will need to be proofed to be tested. It will usually last the longest when kept in a cool, dark place — many people store it in the refrigerator, though refrigeration is certainly not required.

Once packets are opened, they should generally be used within about a month. Spoilage isn’t common, but the granules will sometimes pick up flavors or particles from the outside environment, and exposure to the air can diminish overall strength. Sealing any leftovers in an airtight container can sometimes extend this time frame, but not always.

”Rapid rise” yeast is a type of active dry yeast that is popular for certain “quickbreads” and other recipes that require fast assembly. The granules of this type of yeast are usually so fine as to be more dust than powder, and proofing is often a lot quicker — sometimes only a minute or so. Rising is faster, too.

Either type can be used for most recipes, but bread machine users must often exercise a bit of caution. Bread machine recipes should be followed to the letter, as yeast type can make a big difference when it comes to how the machine responds and processes dough. Rapid rise versions can clog things up or cause dough to rise beyond the baking chamber, which usually leads to major problems.