In the Hebrew we find two distinct words, both translated leaven in the common version of the Bible. This is unfortunate, for there is the same distinction between שׂאֹר, seosr', and חָמֵוֹ, chamets', in the Hebrew, as between leaven and leavensed bread in the English. The Greek ζύμη, appears to be used only in the former sense, and it is doubtful if it applies to a liquid. Chemically speaking, the "ferment" or "yeast" is the same substance in both cases; but "leaven" is more correctly applied to solids, "ferment" both to liquids and solids.
1. שׂאֹר, seir', occurs only five times in the Scriptures, in four of which (Ex 12:15,19; Ex 13:7; Le 2:11) it is rendered "leaven," and in the fifth (De 16:4) "leavened bread." It seems to have denoted originally the remnant of dough left on the preceding baking. which had fermented and turned acid; hence (According to the Lexicon of Dr. Avenarius, 1588) the German sauler, English sour. Its distinctive meaning therefore is fermented or leavened mass. It could hardly, however, apply to the murk or lees of wine.
2. הָמֵוֹ, chamets', ought not to be rendereds "leaven," but leavened bread. It is a more specific term than the former, but is confounded in our translation with it. In Nu 6:3, the cognate noun is applied to wine as an adjective, and is there properly translated "vinegar of wine." In this last sense it seems to correspond to the Greek ὄξος, a sort of acid wine in very common use among the ancients, called by the Latins posca, vinum culpatum (Adam, Rom. Antiq. p. 393; Jahn, Bibl. Archceol. § 144). This species of wine (and in hot countries pure wine speedily passes into the acetous state) [see DRINK] is spoken of by the Talmudists, who inform us that it was given to persons about to be executed, mingled with drugs, in order to stupefy them (Pr 31:6; Sanhedrin, folio 43, 1, c. vi). This serves to explain Mt 27:34. A sour, fermented drink used by the Tartars appears to have derived its name kumiss from the Hebrew chamets'. From still another root comes also מִצָּה, matstsah' (sweet, "without leaven" [Le 10:11]), unleavened (i.e. bread, though in several passages "bread" and "cakes" are also expressed). In Ex 13:7, both seör´ and chamets' occur together, and are evidently distinct: "Unleavened bread (matstsah') shall be eaten during the seven days, and there shall not be seen with the fermented bread (chamets'), and there shall not be seen with thee leavened dough (seör´) in all thy borders." See WINE.
The organic chemists define the process of fermentation, and the substance which excites it, as follows: "Fermentation is nothing else but the putrefaction of a substance containing no nitrogen. Ferment, or yeast., is a substance in a state of putrefaction, the atoms of which are in a continual motion" (Turner's Chemistry, by Liebig). This definition is in strict accordance with the views of the ancients, and gives point and force to many passages of sacred writ (Ps 79:13; Mt 16:6,11-12; Mr 8:15; Lu 12:1; Lu 13:21; 1Co 5:5-8; Ga 5:9). Leaven, and fermented, or even some readily fermentible substances (as honey), were prohibited in many of the typical institutions both of the Jews and Gentiles. The Latin writers use corruptus as signifying fermented; Tacitus applies the word to the fermentation of wine. Plutarch (Romans Quaest. 109:6) assigns as the reason why the priest of Jupiter was not allowed to touch leaven, "that it comes out of corruption, and corrupts that with which it is mingled." See also Aulus Gellius, 8:15. The use of leaven was strictly forbidden in all offerings made to the Lord by fire, as in the case of the meat-offering (Le 2:11), the trespass- offering (Le 7:12), the consecration-offering (Ex 29:2; Le 8:2), the Nazarite-offering (Nu 6:15), and more particularly in regard to the feast of the Passover, when the Israelites were not only prohibited on pain of death from eating leavened bread, but even from having any leaven in their houses (Ex 12:15,19) or in their land (Ex 13:7; De 16:4) during seven days, commencing with the 14th of Nisan. The command was rigidly enforced by the zeal of the Jews in later times (compare Mishnah, Pesach. 2:1; Schöttgen, Horae Hebraicoe, 1:598). It is in reference to these prohibitions that Amos (4:5,) ironically bids the Jews of his day to "offer a sacrifice of thanksgiving with leaven." Hence, likewise, even honey was prohibited (Le 2:11) on account of its occasionally producing fermentation. In other instances, where the offering was to be consumed by the priests and not on the altar, leaven might be used, as in the case of the peace-offering (Le 7:13) and the Pentecostal loaves (Le 23:17). It is to be presumed also that the shew-bread was unleavened, both, á fortiori, from the prohibition of leaven in the bread offered on the altar and because, in the directions given for the making of the shew-bread, it is not specified that leaven should be used (Le 24:5-9); for, in all such cases, what is not enjoined is prohibited. Jewish tradition also asserts that the shewbread was without leaven (Josephus. Ant. 3:6, 6; Talm. Minchoth, 5:2, 3). On Le 2:11, Dr. Andrew Willet observes, "They have a spiritual signification, because ferment signifieth corruption, as St. Paul applieth (1Co 5:8). The honey is also forbidden because it had a leavening force" (Junius, Hexapla, 1631). On the same principle of symbolism, God prescribes that salt shall always constitute a part of the oblations to him (Le 2:16) on account of its antiseptic properties. Thus St. Paul (comp. Col 4:6; Eph 4:29) uses "salt" as preservative from corruption, on the same principle which leads him to employ that which is unfermented (ἄζυμος) as an emblem of purity and uncorruptedness. SEE PASSOVER.
The Greek word ζύμη, rendered "leaven," is used with precisely the same latitude of meaning as the Hebrew seor'. It signifies leaten, sour dough (Mt 13:33; Mt 16:12; Lu 13:21). Another quality in leaven is noticed in the Bible, viz., its secretly penetrating and diffusive power; hence the proverbial saying, "a little leaven leaveneth the whole lump" (1Co 5:6; Ga 5:9). In this respect it was emblematic of moral influence generally, whether good or bad, and hence our Savior adopts it as illustrating the growth of the kingdom of heaven in the individual heart and in the world at large (Mt 13:33). Leaven, or ferment, is therefore used tropically for corruptness, perverseness, of life, doctrine, heart, etc. (Mt 16:6,11; Mr 8:15; Lu 12:1; 1Co 5:7-8; comp. Col 4:6; Eph 4:29). The idea seems to have been familiar to the Jews; compare Otho, Lex Rabbin. Talm. p. 227. They even employed leaven as a figure of the inherent corruption of man: "Alexander, when he had finished his prayers, said, Lord of the universe, it is clearly manifest before thee that it is our will to do thy will: what hinders that we do not thy will? The leaven which is in the mass (Gl., The evil desire which is in the heart)" (Babyl. Berachoth, 17:1; ap. Meuschen, N.T. ex Talmude ill.). We find the same allusion in the Roman poet Persius (Sat. 1:24; compare Casaubon's note, Comment. p. 74). See Wernsdorf, De fermento herodis (Alt. 1724). SEE UNLEAVENED BREAD.
"The usual leaven in the East is dough kept till it becomes sour, and which is kept from one day to another for the purpose of preserving leaven in readiness. Thus, if there should be no leaven in all the country for any length of time, as much as might be required could easily be produced in twenty-four hours. Sour dough, however, is not exclusively used for leaven in the East, the lees of wine being in some parts employed as yeast" (Kitto, Pictorial Bible, 1:161). In the Talmud mention is made of leaven formed of the קולן של סופרים bookmakers' paste (Pesach. 3:1). As the process of producing the leaven itself, or even of leavening bread when the substance was at hand, required some time, unleavened cakes were more usually produced on sudden emergencies (Ge 18:6; Jg 6:19). SEE BAKE; SEE BREAD, etc.