רְתִיחָה, (רָתַח) effervescence, scum, foam. T’bul Yom I, 1 רְתִיחַת … ראשונה the first scum that comes up in boiling groats of beans. Ib. ר׳ יין חדש the scum of new wine. Ib. 2 ר׳ יין ישן the scum of old wine.