How to preserve yeast

In this brief guide, we are going to answer the question “how to preserve yeast” and discuss the different types of yeast and the preservation method for each type of yeast. We will also look at checking the freshness of yeast.

How to preserve yeast

The preservation method depends on the type of yeast. Yeast can be preserved by proper storage, refrigerating and freezing.

  • Active dry yeast, instant yeast and rapid rise yeast: Keeping unopened yeast away from light and moisture and refrigerating or freezing yeast after opening.
  • Fresh yeast: Refrigerating or freezing both before and after opening.

According to research, the global yeast market was valued at around USD 3,230 million in the year of 2016 and it is expected to reach approximately USD 5,417 million by 2022. This market is expected to exhibit a compound annual growth rate, CAGR of around 9% between 2017 until 2022. From the year of 2016, the global yeast market will increase steadily until 2022 (1).

Yeast and its uses in cooking

Yeast is a single-celled microorganism of the fungi kingdom. There are several species of yeast and the type used in baking and brewing is a species called Saccharomyces cerevisiae. 

Yeast (S. cerevisiae) is unicellular, eukaryotic microorganisms, classified in the kingdom of fungi with size ranging from 3-40 µm. The most common mode of vegetative growth in yeast is asexual reproduction by budding. Besides being a model microorganism, the useful physiological properties of yeast led to their use in the field of food and beverage industry and environmental management (3).

Yeast converts the sugars to alcohol and carbon dioxide through a process called fermentation. This process is used in making alcoholic beverages as well as bakery products. The carbon dioxide produced by yeast fermentation is what makes the bread rise giving it its unique texture.

There are three types of yeasts that are widely used in food industries which are the brewery’s yeast in beer production, baker’s yeast in bakery production and nutritional’ yeast in food production. Baker’s yeast produces the CO2 that results in dough leavening and contributes to the flavor and crumb structure of bread. Baker’s yeast is a biotype of S. cerevisiae that can metabolize sugars both aerobically, producing the end products carbon dioxide and water, and anaerobically, producing ethanol and carbon dioxide (1).

Types of yeast used in cooking 

There are several types of yeast used in cooking.

The yeast is produced industrially by aerobic cultivation on various available and inexpensive carbon sources such as molasses. The yeast cells in the wort are then centrifuged and filtered to obtain “wet yeast” with 65–70% moisture, or further dried to obtain “dry yeast” with a moisture as low as 4–6%. The yeast can be granulated and then dried to obtain “instant active dry yeast”. Drying processes are usually based on removal of water by evaporation (2).

  • Active dry yeast: Active dry yeast has a granular texture and it must be proofed by dissolving it in lukewarm. After being proofed, it can be added to the other ingredients. With a solids content of 92-96%, it is shipped as such or in vacuum-packed or nitrogen-flushed pouches. It does not require  refrigerated shipment or storage (4).
  • Instant yeast: Instant yeast has been ground into finer particles than active dry yeast. It can be directly added to dry ingredients without being mixed with water. Drying processes are usually based on removal of water by  evaporation (2).
  • Fresh yeast: Also known as cake yeast or compressed yeast, fresh yeast is moist and perishable and must be refrigerated or frozen at all times. 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 (4).
  • Rapid rise or quick rise yeast: Rapid rise or quick rise yeast has also been ground into fine particles and does not need to be proofed. It also contains additional enzymes that make the dough rise faster.

How to preserve unopened yeast

Unopened, store-bought yeast must be used before the expiry date given by the manufacturer. However, unopened yeast may go bad before the expiry date if it is not stored under the proper conditions (5).

If stored properly yeast may be good to use for 2 yearuse 2 year (5)4 months past its expiry date. The suitability of yeast can be checked by doing a yeast freshness test, which we will discuss later on in this article.

Unopened active dry yeast can usually be stored up to 2 years at room temperature. Dry yeasts have a shelf life of about 1 (active dry yeast) or 2 years (instant active dry yeast) when packed under vacuum or nitrogen  (5). Store it in a cool, dry place, away from direct sunlight. Active dry yeast loses some activity upon storage when exposed to the oxygen of the air. For storage under nitrogen, or when vacuum packed, the loss is about 1 % per month and generally less than 10% per year (4).

Fresh yeast is highly perishable even when unopened, so it must always be refrigerated or frozen. The shelf life of the yeast may also be limited by mold growth after 3-4 weeks of storage (4).

How to preserve yeast by refrigerating

Active dry yeast, instant yeast and rapid rise yeast can be refrigerated to extend its shelf life (6)for about 4 months after being opened. Place the opened yeast in an airtight container or a ziplock bag and refrigerate it until needed.

Fresh yeast must always be refrigerated. Even when refrigerated, the shelf-life of fresh yeast is only about 2 weeks. So it is important not to purchase a large quantity of fresh yeast if you are not planning on using it within 2 weeks.

How to preserve yeast by freezing

Active dry yeast, instant yeast and rapid rise yeast can be frozen for about 6 months after being opened. Place the opened yeast in an airtight container and freeze it until needed.

The shelf-life of fresh yeast can be slightly extended by freezing. Frozen fresh yeast lasts for about 6 months. However, the activity of fresh yeast may deteriorate over time. It is important to check the freshness of yeast before using it in a recipe.

Studies showed that freezing and frozen storage of compressed yeast at –18°C produced an increase of dead cells and caused losses of CO2 production; baking quality reflected the lower specific loaf volume and longer proof times (7).

How to check if yeast is fresh 

Regardless of the storage method, it is always a good idea to check the freshness of yeast before using it in a recipe. Even yeast that is past its expiry date can be used if there are no signs of mold or spoilage and the 

To check the freshness of yeast:

  • Fill a 1 cup liquid measuring cup with ½  cup of warm water.
  • Dissolve 1 teaspoon of sugar.
  • Add one envelope of yeast (2 ¼ teaspoons) and mix until there are no more yeast granules on top. Ensure that the yeast is at room temperature before using
  • Allow the yeast to rise for 10 minutes.
  • After 10 minutes, if the yeast foam has risen to the 1 cup mark, the yeast is still active and good for use.

Other FAQs about Yeast that you may be interested in.

Does Nutritional Yeast Have MSG

What is the best temperature for yeast?

Can you eat nutritional yeast raw?

Conclusion

In this brief guide, we answered the question “how to preserve yeast” and discussed the different types of yeast and the preservation method for each type of yeast. We also looked at checking the freshness of yeast.

If you have any questions or comments, please let us know.

References

  1. Yusof, Abdul Halim, et al. Potential application of pineapple waste as a fermentation substrate in yeast production. Int. J. Sci. Technol. Res, 2020, 9, 1933-1937. 
  2. Akbari, Hamidreza, et al. Optimization of baker’s yeast drying in industrial continuous fluidized bed dryer. Food Bioprod process, 2012, 90, 52-57.
  3. Chandralekha, A., et al. Encapsulation of yeast (Saccharomyces cereviciae) by spray drying for extension of shelf life. Drying technol, 2016, 34, 1307-1318.  
  4. Reed, G., Nagodawithana, T.W. 1991. Baker’s Yeast Production. In: Yeast Technology. Springer, Dordrecht. 
  5. Hidalgo, A., and A. Brandolini. Bread—Bread from Wheat Flour. Encyclopedia of Food Microbiology; Batt, CA, Tortorello, ML, Eds. 2014, 303-308..
  6. Simpson, Estelle, and R. P. Tracey. Microbiological Quality, Shelf Life and Fermentation Activity of Active Dried Yeast]. South Afri J Enol Viticult, 1986, 7, 61-65.
  7. Ribotta, Pablo D., Alberto E. León, and María Cristina Añón. Effects of yeast freezing in frozen dough. Cereal Chem, 2003, 80, 454-458.