Taharos, Chapter 10, Mishnah 4. This chapter has been dealing with the workers of the olive press and the grape harvest and the demands of taharah that rest upon them. Until now olives have held center stage. From this mishnah onward the focus shifts to grapes, and grapes, it turns out, are governed by a stricter rule.
Why grapes are different from olives
One might assume the two are essentially the same. Both are the classic fruits of Eretz Yisrael, both are crushed in order to produce something else, and they share a great deal. But grapes carry an added chumra: grapes that are picked with the intention of being pressed into wine are treated as susceptible to tumah from the very start, already at the moment of the harvest. Consequently the pickers themselves must be tahor, purified people working in taharah. For olives this is not so.
This is the quiet distinction that has been running through the chapter's terminology. The baddadin are the pressers and the botzerin are the pickers. The words do not by themselves specify which fruit is involved. But when the chapter speaks of the pressers it is speaking of olives, because when it comes to olives we simply have no interest in whether the pickers were tamei or tahor. With grapes it is another matter entirely.
The source of the stringency
The reason lies in one of the famous eighteen enactments. On a certain day part of Beis Hillel was absent and did not appear, and Beis Shammai used the opportunity to push through a great deal of legislation. There are eighteen matters in which we follow Beis Shammai rather than Beis Hillel, and this is one of them. The concern of Beis Shammai is that when people handle grapes to inspect them they inevitably press them slightly, a little juice emerges, that juice drips onto other grapes, and once liquid has touched them they become susceptible to tumah, and so on down the line. The upshot is that the entire picking of grapes destined for wine must be carried out betaharah.
The question of a change of mind
Once we accept that, a further question opens up: what happens if the owner changes his mind? Suppose he originally picked the grapes to be eaten, or to be sold for eating, and afterward he decides to bring them to the press and turn them into wine. That is the case of our mishnah.
"Hanosein min hasalim umin hamashte'ach shel adamah." The case is a man who removes grapes from the small baskets, or off a surface where the fruit had been laid out directly on bare soil. Each of these two settings is a recognized sign that the harvest was gathered for eating. Now he takes that fruit and delivers it to the press, which means he has reversed his plan. These grapes came in from a harvest where nobody cared whether the pickers were tahor, they carry the classification of eating grapes, and he wants to reclassify them as pressing grapes and produce wine from them.
"Beis Shammai omrim, nosein beyadayim tehoros. Ve'im nasan beyadayim temei'os, timei'an." According to Beis Shammai he must load them into the press with hands that are tahor, and should he have loaded them with tamei hands, the fruit has become tamei. In other words, Beis Shammai hold that such grapes can now receive tumah despite the fact that eating, not wine, was the original purpose of the harvest, because the owner's new decision by itself reclassifies the fruit and draws it into the category of what can become tamei.
A footnote on the degrees of tumah
There is a difficulty worth pausing over. Hands are ordinarily reckoned as sheni, a second degree of tumah. If so, why should it matter for these grapes? Contact with a sheni would make them shelishi, third degree, and third degree tumah is of no practical consequence for ordinary produce that is not terumah. So what have we accomplished?
Several approaches present themselves. It may be that this reflects a particular position of Beis Shammai. Perhaps we are dealing specifically with grapes of terumah. Alternatively, and more broadly, Beis Shammai maintain that produce still liable to the priestly dues is treated as terumah, so that anything from which terumah will eventually be separated must be handled as terumah from the outset. On that reading, hands of second degree tumah generate third degree tumah in the fruit and thereby disqualify the terumah within it, which is indeed a serious matter. Or it may be that here the hands are treated as rishon, a first degree, a techilah. These are matters of ongoing machlokos, and they are worth turning over in one's mind.
Beis Hillel's position
"Beis Hillel omrim, nosein beyadayim temei'os, umafrish terumaso betaharah." Beis Hillel say that he may place them in with tamei hands, and later, when he separates the terumah from the wine, he must do that part in taharah. Beis Hillel hold that since the grapes were picked with the intention of being eaten, they retain that original status even after the owner's change of mind.
When the grapes were picked for pressing
"Min ha'avtos umin hamashte'ach shel alim." Where he takes the fruit out of the large baskets, or off leaves upon which it had been laid, these are the marks of grapes gathered from the beginning for the press. Here, "hakol shavin shehu nosein beyadayim tehoros." There is no dispute: he loads them with tahor hands. Both houses grant that a harvest carried out with wine in view produces fruit that can receive tumah, and that is how the halachah stands. "Ve'im nasan beyadayim temei'os, timei'an." Should he have loaded them with tamei hands, he has made them tamei.