In this brief guide, we will answer the query, “what is fresh yeast?” and will discuss the difference between dried and fresh yeast.
What is fresh yeast?
Fresh yeast is compressed yeast cells that are still damp. Bakers often utilize a block of fresh yeast cells that includes around 70 percent moisture, also known as cake yeast or compressed yeast. Light beige, soft and crumbly like a pencil eraser, it has an even stronger yeast aroma than dried yeast.
What is yeast?
Single-celled yeast may be found almost everywhere, notably on the surfaces of grains (such as flour made from wheat) and fruits (like grapes). Yeasts are single cell, eukaryotic microorganisms classified in the fungi kingdom. These microscopic fungi are generally about 3–4 μm in size, have a nuclear membrane and cell walls, but unlike plants, they contain no chloroplasts. Yeasts are characterized as heterotrophs in which they rely on living and dead organic material as sources of energy and nutrients. Yeast cells obtain their nutrition by producing and releasing various proteolytic, glycolytic, or lipolytic enzymes to digest organic matter, or by absorbing amino acids and monosaccharides through the cell wall. Yeast consumes sugar from grains and fruits and produces carbon dioxide gas as a byproduct when activated with water (1).
This gas fills the gluten structure of bread dough, causing the dough to puff up and rise. Saccharomyces cerevisiae is the most widely used yeast, even though there are hundreds of distinct types of fungus.
Research has shown that baker’s yeast serves other functions as well. Besides the 2 primary fermentation metabolites, other metabolites such as organic acids, glycerol, and aroma compounds are produced. These compounds have an important impact on the bread making process and final bread quality (2).
Types of yeast
Most bread recipes call for one of four varieties of yeast even though yeast is abundant in nature.
Active dry yeast
This is what most bread recipes ask for when they call for yeast. When active dry yeast was developed in the early twentieth century, it revolutionized the baking industry by becoming the most commercially accessible form of yeast. Yeast granules are protected by a thin layer of gelatin. Warm water activates the yeast, making it active.
Active dry yeast contains about 95% dry matter and comprises 15–25 billion live yeast cells (colony forming units; CFU’s) per gram. The three most common processing methods include tunnel dried yeast (granular powder), fluid-bed dried yeast (quick rise yeast in oval shaped spheroids), and rotolouver dried yeast (produces small spheres or balls). The tunnel dried and fluid-bed drying methods are most common in the U.S., while the rotolouver drying method is more common in Europe and Latin America. Of these drying processes, fluid-bed drying has become the most popular because it causes less damage to yeast cells, and thus, maintains their viability (1).
To make dry yeast dissolve more quickly in the 1970s, adjustments were made to make it more dissolvable. Instant yeast may be added to dry ingredients without the need for activation. Instant yeast is used by both professional and amateur bakers because of its convenience and dependability (active dry yeast is notorious for dying out before it hits its expiration date).
Instant dry yeast is dried in fluid bed dryers. It is most sensitive to loss of activity if it is stored in air and the concentration of oxygen exceeds 0.5% in the gas. Therefore, it is always packaged under vacuum or in an inert atmosphere. It may be added directly to flour and other dry ingredients before the formation of the dough (3).
As the name implies, this fresh yeast is made up of compressed yeast cells that are still damp. In an airtight container, cake yeast may be kept in the refrigerator for two weeks. The refrigerated area of well-stocked supermarkets should have it.
Cake or compressed yeast contains about 30% dry matter. Yeast is grown in large fermenters by the fed batch process. The fermenters are equipped with cooling coils and with means for vigorous aeration to maintain highly aerobic growth. The growth rate is restricted to a growth rate coefficient of less than 0.25. In the fermenter liquid 4-6% of yeast solids can be produced. Post fermentation processing begins with centrifuging to produce a concentrate (yeast cream) with 18-20% solids. The yeast cream is washed and either pressed or filtered to a semisolid yeast mass of 30% solids. This press or filter cake is packaged as a crumbly mass in bags or extruded in blocks that are wax wrapped. It is cooled and shipped refrigerated to bakeries (3).
Most people don’t realize that a sourdough starter (also known as levain) is a kind of yeast. When it comes to bread-rising abilities, certain Saccharomyces cerevisiae strains are used to make commercial yeasts, whereas a sourdough starter utilizes naturally occurring wild yeasts. It has a long lifespan, but it needs regular upkeep.
In addition, food fermentations can be usefully divided into alcoholic fermentations carried out by yeasts, acid fermentations carried out by bacteria, mixed alcoholic / acid fermentations, and fungal (mold) fermentations. Sourdough bread and soda crackers are produced by alcoholic / acid fermentations (3).
What’s the Difference between Dry Yeast and Fresh Yeast?
Dry yeast (both active dry yeast and quick yeast) and fresh yeast (cake yeast). have four major distinctions
The texture of fresh compressed yeast is similar to that of the crumbly block of Feta. Yeast that has been dried, whether active dry, or quick, has the appearance and texture of sand or cornmeal.
Fresh yeast has a substantially shorter shelf life than either instant or active dried yeast. Active dry and instant yeast may be kept at room temperature for many months, however, fresh yeast must be used within a week or two and should not be stored in the refrigerator. The shelf life of instant yeast is the longest of the three commercial yeasts since it has the lowest moisture content. Dry yeast sold in nitrogen-flushed aluminum foil pouches (7 g net weight) has a shelf life exceeding one year (3).
Active dry yeast has to be activated before it can be used in the dough. When the yeast grains are mixed with warm water and whisked until bubbles form, this is done. In both fresh yeast and quick yeast, this step isn’t necessary. When compressed yeast is used, short mixing times are already sufficient to reach maximal fermentation rates. When instant dry yeast is used, however, short mixing times do not allow full rehydration of the yeast cells. Therefore, prolonging the mixing time increased the fermentation rate when instant dry yeast was used. Next to the mixing time, also the method of mixing seemed crucial for rehydrating instant dry yeast (2).
About 25% of the yeast cells are killed during the drying process used to produce active dry yeast. As a result, fermentation is slowed and a noticeable yeasty taste is imparted by these dead yeast cells. Active dry yeast produces less carbon dioxide than fresh yeast and quick yeast because it has a smaller population of live yeast cells.
Buying fresh Yeast
Some stores don’t stock fresh yeast because of its limited shelf life and the fact that it must be refrigerated. Wherever it is, it’s probably on the dairy aisle, near the butter.
It’s important to keep track of the expiry date on fresh yeast to ensure that you don’t waste it. Fresh yeast may spoil quickly due to its perishable nature, so you’ll want to store it in the refrigerator until you need it. Before usage, bring it back to room temperature from the freezer. A moldy or crusted piece of yeast should never be used in a recipe. Storage at elevated temperatures leads to a rapid disappearance of glycogen in the yeast cell, followed by a drop in trehalose concentration, and ultimately autolysis. Studies show that at 5°C there was little loss in activity of fresh yeast over a 4-week period. At 23°C the activity started to drop after 4 days and the yeasts were dead after 20 days. At 35°C the yeasts were practically inactive after 5 days (3).
How to Make Yeast from Dry and Fresh Yeasts?
When converting between dry and fresh yeast, the following ratio should be followed: 2 1/4 teaspoons dry active, instant, or rapid-rise yeast granules (usually one 1/4-ounce packet) = 2/3-ounce fresh yeast. To make things even easier for the baker, Fleischmann’s and Red Star offer their fresh yeast in the same amount of dry yeast as one packet each. 1 gram of active dry yeast should have the same bake activity as 3.1 grams of cake yeast (3).
Uses of fresh yeast
Crumble the fresh yeast before using it. Add it to the dry ingredients or soften in warm water and continue with the recipe after this. As fresh yeast activates more immediately and lasts longer than dried yeast in bread that needs a lengthy, gradual rising time, it is ideal for these types of bread.
Other FAQs about Yeast that you may be interested in.
In this brief guide, we answered the query, “what is fresh yeast?” and discussed the difference between dried and fresh yeast.
- Shurson, G. C. Yeast and yeast derivatives in feed additives and ingredients: Sources, characteristics, animal responses, and quantification methods. Anim feed sci technol, 2018, 235, 60-76.
- Struyf, Nore, et al. Bread dough and baker’s yeast: An uplifting synergy. Comprehen Rev Food Sci Food Safe, 2017, 16, 850-867.
- Reed, G., Nagodawithana, T.W. 1991. Baker’s Yeast Production. In: Yeast Technology. Springer, Dordrecht.