We are studying Mishnah 7 of the eighth chapter of Maseches Menachos, the last mishnah in the chapter and the last in the series of mishnayos dealing with the preparation of the wine for the Beis HaMikdash. The mishnah deals with how the wine was stored and how it was drawn from the barrel.
Storing the wine in barrels:
"Lo hayu konsin oso b'chatzavim gedolim ela b'chaviyos ketanos" - the wine was not stored in large vessels, but in small barrels. The reason: in a large barrel the wine is liable to spoil and become damaged, since emptying it takes a long time. Such a barrel is used over the course of several days, and with each and every opening more air enters the barrel, causing oxidation and spoilage. Compare it to a bottle of wine, which is meant to be used in a single day, and which one does not leave open for a week.
"V'eino memaleh es hechaviyos ad pihen k'dei sheyehei reicho nodef" - when filling the barrel one does not fill it to the top, but leaves a space between the surface of the wine and the mouth of the barrel, so that the aroma of the wine can spread. There are two approaches to explaining this:
The first approach: the purpose is the wonderful aroma that rises from the barrel when it is opened, and the space at the top makes this possible.
The second approach: the volatile alcohol that evaporates at the top of the barrel forms a barrier that prevents air from penetrating inside, and in this way the wine stays fresh over time.
"Eino mevi lo mipiha mipnei hakemachin v'lo mishuleha mipnei hashemarim" - when taking the wine out of the barrel, one does not draw from its upper part, because of the kemachin. 'Kemachin', from the word kemach (flour), is a term for the white pieces that float on the surface of the wine. Some explain that these are lees that float on top, and some explain that it refers to mold. Similarly, one does not draw from the very bottom of the barrel, because of the lees: the sediment and the dead yeast sink to the bottom of the barrel, and even in foreign languages the expression 'the dregs of society' is derived from the residue at the bottom of the barrel.
"Ela mevi mishlishah um'emtza'ah" - the straightforward reading is to take the wine from the middle third of the barrel: not from the top and not from the bottom, but from the clear wine in the middle, which contains neither the kemachin at the top nor the lees at the bottom.
"Keitzad hu bodek?"
While the wine is flowing from the barrel into the vessel, how can one make sure that the sediment in the barrel has not begun to come out along with it? To this the mishnah says: "Hagizbar yoshev v'hakaneh b'yado" - the treasurer, the official appointed by the Beis HaMikdash, sits and supervises the wine as it comes out, with a reed in his hand. 'Kaneh' is usually understood as a reed, and many explain that it is like a walking stick or a staff that signifies his authority.
"Zarak hagid hikish bakaneh" - when the stringy matter begins to come out of the wine barrel into the vessel, at that very moment the treasurer strikes with the reed. There are two approaches to explaining this act:
The first approach: he strikes the barrel in order to signal to the one pouring to stop the flow of the wine, since the stringy substance has begun to come out with it. And why does he not announce it out loud? Because one does not speak near the barrels, since the breath and air that come out of a person's mouth are harmful to the wine.
The second approach: the striking is not a signal to another person; rather, the treasurer strikes the stream of wine itself and diverts it to the side, so that the wine containing the stringy substance will not enter the vessel in which the wine is being collected.
Some have the reading "zarak hagir" instead of "hagid". According to this version the reference is to a white, chalk-like substance, and when it begins to come out the treasurer stops the flow - either by signaling to the one pouring, or by diverting the stream himself.
The View of Rabbi Yosi bar Avida:
The mishnah closes with the words: "Rabbi Yosi bar Avida omer: yayin she'alah bo kemachin pasul" - any wine that has developed kemachin, those whitish specks that float on its surface, is disqualified. He brings a proof from two verses: "Temimim yihyu lachem u'minchasam" - that the offering and its meal offering must be unblemished; and likewise "Temimim yihyu lachem v'niskeihem" - that the libations themselves must also be unblemished. In both cases the idea is the same: nothing foreign should be found in them, such as that white residue floating on top of the barrel of wine.
If the kemachin are simply sediment, it is hard to understand the disqualification, since this is a natural occurrence in a barrel; but if we are speaking of mold, the matter is readily understood, since one does not want mold in the wine. In any event, the halachah does not follow Rabbi Yosi bar Avida but rather the first opinion in the mishnah, and according to that view those white lees that rise to the surface are part of the process by which wine is produced, and they may even be a good sign that the wine is fermenting properly - only that they should not be collected into the vessel used for the libations.
In summary: In this mishnah we learned the laws of storing the wine and drawing it off for use in the Beis HaMikdash: that it is gathered specifically into small barrels, that they are not filled to the brim, that the wine is drawn from the middle of the barrel and not from its top or its bottom, and the role of the treasurer who sits with the reed in his hand to stop the flow the moment the residue appears. We also examined the view of Rabbi Yosi bar Avida, who disqualifies wine that has developed kemachin based on the requirement of "Temimim yihyu lachem," and the fact that the halachah does not follow him.