Uktzin, Chapter 3, Mishnah 7. Our masechta returns repeatedly to one central question: which items carry the halachic status of ochel, food, so that they can become tamei with tumas ochlin. This mishnah presents three cases where that question is in dispute, and the cases move from fruit that is not yet ready, to fruit that never became soft, to a seed that is eaten only as a flavoring.
Pagin and bosser
"Hapagin vehabosser". The term pagin refers to figs that have not yet ripened, and bosser to grapes still in their immature state. Do such fruits already qualify as food?
"Rebbi Akiva metamei tumas ochlin." Rebbi Akiva rules that they do carry the status of food and can therefore become tamei. Although they have not ripened, people do in fact eat them in that state, and that is enough to place them in the category of ochel.
"Rebbi Yochanan ben Nuri omer, mishyavo'u le'onas hama'asros." Rebbi Yochanan ben Nuri sets a later boundary. Only once the fruit has reached the stage known as onas hamaasros does it become subject to tumas ochlin. That is the stage of development at which fruit becomes obligated in maaser, when it has begun to ripen. Before that point, as long as the fruit is still properly labeled pagin or bosser and has not yet begun to ripen at all, it is not yet food and is not susceptible to tumah.
Peritzei zeisim va'anavim
"Peritzei zeisim va'anavim." The word poretz means to break through or to breach. Sometimes when olives are pressed, certain olives are so hard and unripened that the pressure of the press cannot crush them. Instead of yielding their oil, they shoot out and burst away from the press, breaking out from under the pressure. The same happens with especially hard grapes. These are the peritzei zeisim va'anavim of our mishnah.
"Beis Shammai metam'in, uveis Hillel metaharin." In the opinion of Beis Shammai, hardness notwithstanding, these olives and grapes retain the status of ochel and can contract tumah. Beis Hillel disagree and declare them tahor: once they have hardened in this way, they no longer belong to the category of food.
Haketzach
"Haketzach." Ketzach is identified by some as caraway seed, known as kimmel, the seed that is baked into bread.
"Beis Shammai metaharin." Here the two houses reverse their positions from the previous case. Beis Shammai rule that ketzach is tahor, since a person does not eat these seeds on their own. They function purely as an enhancement, a flavoring for the bread.
"Uveis Hillel metam'in." Beis Hillel rule that ketzach is capable of becoming tamei. Since it is eaten together with the bread, it takes on the character of food and enters the laws of tumas ochlin.
The same dispute for maasros
The mishnah concludes, "vechein lema'asros", that the identical dispute applies to the obligation of tithing. The debate between Beis Shammai and Beis Hillel is really a debate about whether ketzach is defined as ochel, and that definition governs more than tumah alone. According to the view that ketzach counts as food, it is obligated in maasros and a person must tithe it. According to the view that it is not food, and therefore is not subject to tumas ochlin, it is likewise exempt from maasros.
Three cases, one question. Whether a fruit has ripened enough, whether a hardened olive still belongs among foods, and whether a seed eaten only for flavor joins the bread it flavors: in each instance the Tannaim are measuring how much a thing must resemble ordinary food before the halachos of ochel take hold of it.