\ˈyēst, especially Southern and Midland US ˈēst\

Definition of yeast 

(Entry 1 of 2)

1a : a yellowish surface froth or sediment that occurs especially in saccharine liquids (such as fruit juices) in which it promotes alcoholic fermentation, consists largely of cells of a fungus (such as the saccharomyces, Saccharomyces cerevisiae), and is used especially in the making of alcoholic liquors and as a leaven in baking

b : a commercial product containing yeast fungi in a moist or dry medium

c(1) : a unicellular fungus that is present and functionally active in yeast, usually has little or no mycelium, and reproduces by budding

(2) : any of various similar fungi

2 archaic : the foam or spume of waves

3 : something that causes ferment or activity were all seething with the yeast of revolt— J. F. Dobie


yeasted; yeasting; yeasts

Definition of yeast (Entry 2 of 2)

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Other Words from yeast


yeast-like or less commonly yeastlike \ˈyēst-ˌlīk, especially Southern and Midland US ˈēst- \ adjective

Examples of yeast in a Sentence


taxation without representation proved to be the yeast of rebellion

Recent Examples on the Web: Noun

Jews prepare for Passover by cleaning out their homes to remove all leaven, such as bread, rice, flour and yeast. Greg Garrison,, "What is Passover? Here are some facts about the biblical holiday," 30 Mar. 2018 In a large bowl, stir together the flour, yeast, and salt. Alex Van Buren,, "Making No-Knead Bread Is So Much Easier Than You Think—and You’ll Use It in Meals All Week Long," 23 May 2018 The ingredient, made from soybean roots and genetically engineered yeast, goes into vegetarian Impossible Burgers, which are available in a growing number of restaurants — even fast-food stalwart White Castle. Lydia Mulvany, The Seattle Times, "Impossible Foods fights for FDA approval on its meatless burgers," 23 Apr. 2018 Parmesan or even a pinch of nutritional yeast adds extra oomph. Sara Franklin, charlotteobserver, "No courses, no assigned seats, no-hassle dinner party," 19 June 2018 At the massive red barn of Big Oyster’s new location in Lewes, an element of wild yeast and barrel-aging adds extra levels of complexity. Craig Laban,, "Sipping Delaware beer coast's colorful sours," 15 June 2018 For decades, stateside brewers have increasingly dabbled in sour beer and wild fermentation, tinkering with non-traditional yeasts, bacteria and rule-breaking media. Keith Flanagan, USA TODAY, "The latest beers are inspired by booze," 12 June 2018 The major difference between types of beer comes down to the type of yeast used to ferment it. Mahita Gajanan, Time, "How to Talk About Beer Like a Pro on National Beer Day," 7 Apr. 2018 Winemakers who steer clear of commercial yeast, synthetic pesticides, or large amounts of added sulfur often offer easy-drinking wines from grapes fermented to emphasize bright, fruity flavors. Maggie Hoffman, Sunset, "8 Chilled Red Wines Perfect for Summer Sipping," 22 Jan. 2018

Recent Examples on the Web: Verb

Same for dozens of styles of fish stew, yeasted rolls, cakes, and pies found around the world. National Geographic, "The Secret History of the World's Priciest Spice," 3 May 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'yeast.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of yeast


before the 12th century, in the meaning defined at sense 1a


1819, in the meaning defined above

History and Etymology for yeast


Middle English yest, from Old English gist; akin to Old High German jesen, gesen to ferment, Greek zein to boil

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Statistics for yeast

Last Updated

18 Oct 2018

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Time Traveler for yeast

The first known use of yeast was before the 12th century

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More Definitions for yeast



English Language Learners Definition of yeast

: a type of fungus that is used in making alcoholic drinks (such as beer and wine) and in baking to help make dough rise


\ˈyēst \

Kids Definition of yeast

1 : a single-celled fungus that ferments sugar to produce alcohol and carbon dioxide

2 : a commercial product containing living yeast cells that is used in baking to make dough rise and in the making of alcoholic beverages (as wine)


\ˈyēst \

Medical Definition of yeast 

1 : a unicellular chiefly ascomycetous fungus (as of the family Saccharomycetaceae) that has usually little or no mycelium, that typically reproduces asexually by budding, and that includes forms (as Saccharomyces cerevisiae) which cause alcoholic fermentation and are used especially in the making of alcoholic beverages and leavened bread

2 : a yellowish surface froth or sediment that occurs especially in sugary fermenting liquids (as fruit juices) and consists chiefly of yeast cells and carbon dioxide

3 : a commercial product containing yeast cells in a moist or dry medium

Other Words from yeast

yeastlike \-ˌlīk \ adjective

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Comments on yeast

What made you want to look up yeast? Please tell us where you read or heard it (including the quote, if possible).


a state of commotion or excitement

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