lac·​tose | \ˈlak-ˌtōs, -ˌtōz\

Definition of lactose 

: a disaccharide sugar C12H22O11 that is present in milk and yields glucose and galactose upon hydrolysis and yields especially lactic acid upon fermentation

Examples of lactose in a Sentence

Recent Examples on the Web

The process of fermenting milk into cheese also reduces its lactose content, because much of it drains away with the liquid whey. Kiona N. Smith, Ars Technica, "Early cheese making may have helped lactose-intolerant farmers spread," 14 Sep. 2018 Polar bear milk has almost ten times as much fat and protein as cow's milk, almost no lactose. Bob Gathany,, "Up in the air at the Huntsville Community Kite Festival," 4 Mar. 2018 To make it, dairy producers have long employed the help of Streptococcus thermophilus, a bacteria that gobbles up the lactose in milk and poops out lactic acid. Megan Molteni, WIRED, "The WIRED Guide to Crispr," 27 Apr. 2018 Glutard, then, is a disparaging term for a person who doesn’t eat gluten, lactard for someone who can’t tolerate lactose, and libtard for a liberal. Melissa Mohr, The Christian Science Monitor, "When good words turn bad," 28 June 2018 Nut and seed milks are a delicious lactose-free alternative to traditional dairy milk, and they can be used in a variety of recipes that require the real thing. Time, "Weekend Recipe: Your Guide to Creating Dairy-Free Nut, Seed and Rice Milks," 22 June 2018 The cholesterol-free rolls are entirely vegan, with no use of dairy, lactose or eggs, the release said. Wesley Case,, "Vegan bakery Cinnaholic to open in Hampden in early June," 23 May 2018 Gone are the days of gritting your teeth through gritty soy lattes to avoid the gastrointestinal effects of lactose and dairy fat; a new, smoother, tastier league of mylks has arrived to appease dairy haters of every ilk. Marian Bull, GQ, "The Best Non-Dairy Milks for Every Occasion," 12 June 2018 Or the large percentage of individuals who have trouble digesting lactose, the sugar in milk, and prefer something other than dairy milks that may be more easily digested. Lisa Drayer, CNN, "Got alt-milk? How plant-based alternatives compare," 31 May 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'lactose.' 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 lactose

1857, in the meaning defined above

History and Etymology for lactose

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Statistics for lactose

Last Updated

17 Nov 2018

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Time Traveler for lactose

The first known use of lactose was in 1857

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More Definitions for lactose



English Language Learners Definition of lactose

chemistry : a type of sugar that is present in milk


lac·​tose | \ˈlak-ˌtōs \

Kids Definition of lactose

: a sugar that is found in milk


lac·​tose | \ˈlak-ˌtōs, -ˌtōz \

Medical Definition of lactose 

: a disaccharide sugar C12H22O11 that is present in milk, yields glucose and galactose upon hydrolysis, yields especially lactic acid upon fermentation, and is used chiefly in foods, medicines, and culture media (as for the manufacture of penicillin)

called also milk sugar

More from Merriam-Webster on lactose

Rhyming Dictionary: Words that rhyme with lactose Encyclopedia article about lactose

Comments on lactose

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living or existing for a long time

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