'yolk-containing' is a compound of the noun 'yolk' and the present participle/adjective-forming element 'containing'. 'yolk' originates from Old English 'geolc'/'geolu' (related to 'yellow'), where the root meant 'yellow'; 'contain' originates from Latin 'continere' via Old French and Middle English, where 'continere' meant 'to hold together.'

'yolk' changed from Old English 'geolc'/'geolu' into Middle English as 'yolk' and kept its association with the yellow inner part of eggs. 'contain' transformed from Latin 'continere' to Old French 'contenir' and Middle English 'containen/containen' and eventually modern English 'contain', with the participial/adjectival form 'containing' used to form compounds like 'yolk-containing.'

Initially, 'yolk' primarily signified the yellow color or the yellow part of an egg, and 'contain' meant 'to hold'; combined as 'yolk-containing' the compound straightforwardly came to mean 'holding or having yolk' and has retained that literal meaning in modern usage.