Exegesis:

homoia estin zumē ‘it is like yeast,’ cf. on 12.1.

hēn labousa gunē enekrupsen eis aleurou sata tria ‘which a woman took and hid in three measures of flour.’ For the aorist tenses in v. 21 cf. on v. 19.

egkruptō ‘to hide,’ ‘to cover up,’ or, ‘to put into,’ since here the hiding of the yeast is not the purpose, but the result of the woman’s act. The purpose is indicated by the subsequent clause.

aleuron ‘wheat flour.’

saton transliteration of Aramaic sata or seah, a measure of capacity, of a little less than three gallons, or about thirteen L. (cf. Strack-Billerbeck I, 669f).

heōs hou ezumōthē holon ‘till it was all leavened.’ holon is adjective. It is modified by the subject of ezumōthē, i.e. aleuron understood from the preceding clause, and indicates that the leavening affected all of the flour.

zumoō ‘to ferment,’ ‘to leaven.’

Translation:

Leaven, see 12.1; here used as a metaphor for an all-pervading good influence.

Which a woman took … may have to become a conditional or temporal clause as in v. 19.

Hid, preferably ‘put,’ or more specifically, ‘mixed’ (e.g. Javanese), ‘kneaded,’ or another term by which the receptor language normally refers to this activity.

Three measures, or, ‘three baskets’ (Toraja-Sa’dan), “a bushel” (An American Translation, Good News Translation), ‘one barrel’ (Sranan Tongo), or any other expression designating a fairly large quantity of meal.

Meal, or, ‘wheat-flour,’ ‘rice-flour,’ has sometimes to be described, cf. ‘dry seed (that is) ground’ (Chicahuaxtla Triqui for Rev. 18.13).

Till here introduces an event that takes place some time after and a the result of the preceding act; hence, ‘(and) after-some-time’ (Bahasa Indonesia RC), or, ‘so-that’ (Malay).

It … all, i.e. ‘all the flour, or, bread dough.’

Was … leavened, or ‘became sour,’ ‘had fermented,’ ‘was swollen up,’ ‘became salted’; often dependent on the term for ‘leaven/yeast.’

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.