An Etymological Dictionary of the German Language/gären

by Friedrich Kluge

gären, vb., ‘to ferment, effervesce, bubble,’ a combination as to its form of a str. vb. MidHG. gëren; jësen; OHG. jësan, ‘to ferment, foam,’ and the corresponding factitive MidHG. *jern (unrecorded, but OHG. jęrian occurs), ‘to cause to ferment’; OHG. jësan is a str. vb., and jęrjan a wk. vb. (comp. ginësan str. vb., and ginęrian, wk. vb.). Noun derivatives of the Teut. root jes retain their s (before t) even as late as ModHG.; see Gischt, under which the cognate nouns from the other OTeut. dialects are brought together. The root jes, yes, occurs also in Ind. and Gr.; comp. Gr. ζεσ-τός, ‘boiled,’ ζέσ-μα, hence also ζέω for *ζέσω (perf. ξεσ-μαὸ), ‘to boil, bubble’ (ζ for earlier j, y as in ζυγόν, see Joch), Sans. root yas, ‘to seethe, boil.’ Considering this agreement of forms with initial j and y, ModHG. gären with g is remarkable; so too OIc. gerþ, ‘yeast’ (but E. yeast).