Bava Metzia, Chapter 7, Mishnah 4. The Mishnah continues to discuss the right of a worker to eat from the produce he is working with. The basis for this law is the verse "Ki tavo becherem re'echa ve'achalta anavim" - when a person comes, as we understand based on tradition, to work in the vineyard of his fellow Jew, he is permitted to eat from the grapes. From here, the Sages understood that he may eat specifically from the grapes, because he is working in the vineyard, and not from another species of produce.
Eating from a species the worker is not engaged with:
The question is what the law is regarding a person who is hired to harvest grapes, but in order to reach them, he must pass through the fig orchard of that same employer; or he knows for certain that in the morning he will harvest grapes and in the afternoon he will pick figs. Is he allowed to eat from both species? The answer is negative: he may only eat from the species that he is engaged with at that specific time.
In the words of the Mishnah: "Hayah oseh vete'enim lo yochal ba'anavim, ba'anavim lo yochal bate'enim" - a worker engaged with figs is forbidden to eat grapes, and even if he passes through the vineyard or knows that he will work with grapes later in the day, it is of no consequence. And similarly the other way around: a worker engaged with grapes is forbidden to eat figs.
"Mone'a atzmo ad shemagi'a lemakom hayafos":
What the worker is permitted to do is as follows: "Aval mone'a atzmo ad shemagi'a lemakom hayafos ve'ochel" - he is allowed to save his appetite. The case of the Mishnah is a worker harvesting grapes and advancing from north to south, and he knows that the grapes on the southern side, the place where the sun shines, are sweeter. If his desire is to wait until he reaches the southern side of the vineyard and only then to eat, he is completely permitted to do so, and there is no prohibition involved.
Furthermore, even though the Mishnah does not state this explicitly, if he works with grapes in the morning and figs in the afternoon, and he prefers figs over grapes (and even if the figs are more expensive than the grapes, it makes no difference), he is allowed to save his appetite and not eat from the grapes until he reaches the figs.
"Bekol elu lo amru ela bish'as melachah":
All of this permission, the right of the worker to eat from the produce he is engaged with (assuming the conditions explained in the previous Mishnayos have been met), only applies while he is actively engaged and actually working with the produce. But a worker passing from vineyard to vineyard, from section to section, or from row to row, is not engaged with the grapes at that moment but is rather walking, and therefore his right to eat from them is suspended at that moment. These are the rules established by the Torah.
Rabbinic enactment to return a lost item to the owner:
However, the Sages intervened, as in the words of the Mishnah: "Aval mishum hashavas aveidah labe'alim" - in order to save the employer money. Returning a lost item here means restoring a loss, and this is indeed the essence of this mitzvah: returning lost objects is about preventing any loss or ongoing loss to another Jew. One who sees his friend's car running, or the lights and air conditioning left on when no one is home, has an obligation to help and turn them off in order to save him money.
Here too, the Sages said that the employer strongly prefers that the workers harvesting his grapes eat them while walking from one section of the vineyard to another, and not while they are actively harvesting. This is because when their hands are free for harvesting, they will harvest more grapes, whereas when their hands are busy eating, the output decreases. It turns out that for the benefit of productivity, the economic interest of the employer himself is to permit the workers to eat while moving between the sections, even though they are not actively engaged with the grapes at that time. Therefore, the Sages established that this is permitted.
Therefore, the Mishnah says: "Aval mishum hashav aveidah labealim amru: poalim ochalin bahalichatan me'uman le'uman, uvachazaratan min hagat" - workers are permitted to eat while walking from one row or section in the vineyard to another, and the same law applies when they return from the winepress.
"Uvachamor keshehi poreket" - and a donkey while it is being unloaded:
Here ends the first part of the Mishnah, and this is where a period belongs. The language of the Mishnah can be misleading, since the last words begin with the letter "vav" ("and"), as if they are a continuation of the previous matter: "uvachamor keshehi poreket". However, in fact, this is a completely new topic that requires a new paragraph, and it could even have stood as a Mishnah on its own.
We have already mentioned that there is a separate mitzvah in the Torah: "Lo tachsom shor bedisho" - it is forbidden to muzzle an ox while it is threshing on the threshing floor. We said that there is a certain parallel to this even for human beings, but let us return to animals. One might mistakenly think that the Torah's intention is that when the animal is working on the threshing floor, it sees the grain, drools, and very much wants to eat from it; and if its mouth is muzzled, it suffers and is taunted - a taunting where it sees the food and cannot eat it. According to this, it would emerge that if the animal does not see the food, there is no reason to forbid muzzling it or preventing it from eating.
Therefore, the Mishnah comes and teaches a novel concept: a donkey carrying a load on its back - even though it does not see what is on its back, it is forbidden to prevent it from eating from it. For example, if a stalk hangs down from its back to a place it can reach by tilting its neck, or if a little of the load falls and the donkey sees it, or if it sees the load on the back of another donkey walking alongside it. In whatever case it may be, the rule is that donkeys, when they are engaged in transporting and carrying produce, are working for the owners, and therefore have the right to eat from what they are carrying - in whatever way they might have access to it - and it is forbidden to prevent them.
Practically, as the Shulchan Aruch rules, there is no obligation to actively feed the animals, nor to let them eat from other species during their work. The prohibition is only against preventing and hindering them from eating what is on their backs, as long as it is on their backs. However, once the load is unloaded from the donkey's back, it is once again permitted to prevent it from eating from that grain.
In summary: In this Mishnah we learned that a worker only eats from the species he is working with at that time, even if he passes through another orchard or will work in it later in the day; that he is allowed to restrain himself and save his appetite until he reaches the better quality fruit; that the right to eat is only during actual work, except that in order to avoid a loss to the owners, the Sages permitted eating even while walking from row to row and returning from the winepress, since this is for the benefit of the employer himself; and in the second part - that even a donkey carrying a load is entitled to eat from it, as long as it has not been unloaded from its back.