What does agar mean?
Agar is a gelatinous substance extracted from certain red seaweeds, chiefly species of Gelidium and Gracilaria. Chemically a complex polysaccharide, it has the remarkable property of dissolving only in boiling water while remaining firm at temperatures far above room temperature — unlike animal gelatin, which melts easily. This stability made agar indispensable to microbiology: since the late nineteenth century it has been the standard gelling base for culture media in petri dishes, allowing scientists to grow and study bacteria and fungi on solid surfaces. Beyond the laboratory, agar serves as a vegetarian and vegan gelling agent in desserts, jellies, and confectionery, marketed in some regions under its original Malay name 'agar-agar'. Derived fractions such as agarose are central to molecular biology techniques like gel electrophoresis. The word entered English through trade with Southeast Asia, and today agar stands as one of the most consequential substances ever borrowed from traditional Asian cookery into modern science.
nounA gelatinous substance obtained from certain red seaweeds (notably Gelidium and Gracilaria species), used especially as a culture medium in microbiology and as a gelling agent in food.
- A gelatinous polysaccharide extracted from red seaweed, used as a solid culture medium for microorganisms in laboratories.
- The same substance used as a vegetarian gelling or thickening agent in foods such as desserts, jellies, and confectionery.
"The bacteriologist streaked the sample across an agar plate and left it to incubate overnight."
"The lab technician poured molten nutrient agar into sterile petri dishes before inoculating them with bacterial cultures."
"Vegan cooks often substitute agar for gelatin when making fruit jellies and panna cotta."
Rarely used; 'agars' appears mainly in technical writing referring to different types or grades of agar rather than multiple quantities of the substance.
"The supplier stocks several agars, including bacteriological-grade and food-grade varieties."
In 1882, microbiologist Walther Hesse's wife Fanny suggested agar — a gelling agent she knew from her grandmother's jam recipes — and it replaced gelatin in petri dishes worldwide because bacteria can't digest it.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of agar
Agar derives from the Malay–Indonesian term 'agar-agar', the name by which the gelling seaweed product was known in Southeast Asian cuisine. The word entered European languages during the nineteenth century through trade contacts with the region, and English adopted it around the 1880s, coinciding with its introduction into laboratory practice. Its adoption in microbiology is traditionally credited to Fanny Hesse, who suggested it to her husband Walther Hesse working in Robert Koch's laboratory in 1882. The Malay compound 'agar-agar' itself remains in use, particularly in food contexts.
Related word forms
How agar is actually used
Agar is a mass (uncountable) noun in most contexts; it appears in scientific register almost exclusively in compounds like 'agar plate' or 'agarose gel'. In culinary contexts it is sometimes called 'agar-agar', reflecting its Malay source term, and is valued as a vegan alternative to gelatin.
Easily confused with agar
Gelatin is an animal protein derived from collagen that melts near body temperature, whereas agar is plant-derived from seaweed and remains solid well above room temperature.