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Bible Dictionaries
Leaven
Hastings' Dictionary of the New Testament
or LEAVEN.—The effect of leaven upon dough to which it is added is due to minute living organisms disseminated through it in great numbers. These organisms are one or more species of yeast-fungi. They are the most important agents of the alcoholic fermentation, which they produce in dough as well as in solutions of sugar. Whether lodged in sour dough (leaven) or collected free out of fermenting vats (compressed yeast), they cause the same effect when introduced into bread sponge. At the present time leaven is not so much used for the lightening of bread as yeast, because it is apt to impart to bread a sour taste and a disagreeable odour.
Yeast-fungi were first recognized (1680) by the Dutch naturalist Leuwenhöck in the scum floating on the surface of fermenting beer. With his imperfect lenses he was able to observe little of their structure beyond the fact that they were very small globules. They are now known to be single-celled plants, having for the most part an oval or ellipsoidal shape. The individual yeast-cell consists of a mass of protoplasm enclosed in a delicate wall of cellulose. The protoplasm, as in the case of all the fungi, contains no chlorophyll, and is, accordingly, dependent upon organic matter for its nourishment. It is granular, and usually shows one large non-contractile vacuole or several small vacuoles containing water. It has also a nucleus, which, however, can be brought into view only after special treatment. The size of the yeast-cell varies from 1.5 microns to 15 microns in diameter. (The micron equals 1/25000 inch). During the inactive stage the cells are isolated, but in an actively fermenting medium they occur in groups or families, organically united and consisting of from two to six or eight members in varying stages of development. When the members reach maturity, they separate from one another, each one having the capacity to produce a new group. This is the method by which the plant propagates itself. An isolated cell sends out a little pimple or bud on the surface. The bud is destined to become an independent cell of the same size as the cell which produced it; but, before it is mature, it may itself form a bud which in turn may form another bud of its own, the mother-cell in the meantime forming a second bud at a different point. A sort of chain of sprouts, usually curved, is formed as the result of this process of budding or gemmation. The successive buds round up and finally separate themselves as independent individuals. Pasteur, to whose elaborate investigations we are deeply indebted for our knowledge of the agents and the process of fermentation, found that two cells produced eight in two hours at a temperature of 13 degrees C. The multiplication is more rapid at a higher temperature.
Yeast-fungi secure their food for the most part from weak solutions of grape-sugar. They convert grape-sugar into alcohol and carbon dioxide. This conversion is known as the alcoholic fermentation. The same action takes place in moistened wheat-flour when yeast is mixed with it. The wheat grain contains a ferment, diastase, whose function is the conversion of the insoluble starch of the grain into soluble grape-sugar for the nourishment of the embryo when the grain germinates. Diastase is present, of course, in wheat-flour, and when the conditions of moisture and temperature are supplied, as in a gently heated bread sponge, it effects the same conversion as under natural conditions in the germinating grain. Some of the flour starch is changed into grape-sugar, in which the yeast-cells excite the alcoholic fermentation. The bubbles of the gas carbon dioxide produced in the fermentation are entangled in the glutinous sponge, and, expanded by heat, puff it up or lighten it. If, now, more flour is thoroughly mixed with this sponge so as to scatter the yeast-cells of the sponge throughout the mass, the whole will shortly be leavened by the gas which continues to be given off by the agency of the rapidly multiplying cells. A practically indefinite quantity of flour so treated can be leavened by ‘a little leaven.’
The week which began with the Passover is called ‘the days of unleavened bread’ (Matthew 26:17, Mark 14:1; Mark 14:12, Luke 22:1; Luke 22:7), from the practice enjoined in Exodus 23:15, Leviticus 23:6, Deuteronomy 16:3-4; Deuteronomy 16:8.
The effect of leaven in raising a mass of dough (see above) is the basis of our Lord’s parable of the Leaven (Matthew 13:33, Luke 13:20-21), which sets forth the gradual and pervasive influence of the Kingdom of God upon the whole of human society.
The fermentation produced by leaven was regarded as a species of putrefaction, and this, together with the tendency of leaven to spread, explains the figure in which ‘the leaven of the Pharisees and Sadducees’ stands for their corrupt teaching (Matthew 16:6; Matthew 16:11, Mark 8:15), or, as St. Luke puts it more specifically in the case of the Pharisees, their hypocrisy (Luke 12:1). ‘The leaven of Herod’ (Mark 8:15) similarly denotes the policy of the Herodian party.
Literature.—Trench, Dods, Bruce, Orelli on the Parables; Winterbotham, Kingdom of Heaven, 70; Drummond, Stones Rolled Away, 144; Scott-Holland, God’s City, 143; Macmillan, Two Worlds are Ours, 153; R. Flint, Christ’s Kingdom, 170.
W. L. Poteat and James Patrick.
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Hastings, James. Entry for 'Leaven'. Hastings' Dictionary of the New Testament. https://www.studylight.org/dictionaries/eng/hdn/l/leaven.html. 1906-1918.
