This Mishnah discusses workers who are hired to work with Neta Reva'i produce. Neta Reva'i produce is produce during its fourth year of growth. During the first three years, the produce is called Orla, and it's prohibited to have any benefit from it. During its fourth year, the fruit has to be taken to Yerushalayim (Jerusalem) and eaten there. If it can't be transported to Yerushalayim, it is eventually redeemed for money, and that money is taken to Jerusalem and used to buy food there. So here we'll talk about Neta Reva'i, which is not eaten outside of Yerushalayim unless it's redeemed for money. That's what the worker is working with.
HaSocher et haPo'alim la'asot b'neta Reva'i shelo. Harei elu lo yochlu. If somebody is hiring workers to harvest his Neta Reva'i fruit, harei elu lo yochlu. The worker is not allowed to eat that fruit. While they're working with it, Neta Reva'i fruit is not allowed to be eaten outside of Yerushalayim, and the employer does not have to redeem the fruit to make it accessible and permissible for the worker to eat. If the workers accepted the job knowing that they're dealing with Neta Reva'i fruit, they understand that there won't be the perk of eating while they work. But the Mishnah continues: Im lo hodi'am, but if the employer didn't understand, informed the workers that they were being hired to harvest Neta Reva'i fruit, which they weren't allowed to eat, Podeh u'ma'akhilan. Then the employer has to redeem the Neta Reva'i fruit, put the holiness of those fruits onto coins, and eventually transport those coins to Yerushalayim. Once he does that, he removes the holiness from the produce itself and allows the workers to eat from it. Since the workers accepted the job in this scenario expecting that eating the produce would be a perk of their job, the employer has to arrange for them to be able to do so. So if he never informed them beforehand that they were dealing with Neta Reva'i, he has to redeem the produce and give them some of this fruit to eat.
We learned in a Mishnah bet that a worker doesn't have the right to eat from the produce anymore once it's detached from the ground and fully processed. This is the Gemar Melacha: once the produce is fully processed, it's obligated in terumot u'ma'asrot (priestly offerings and tithes), and until terumot u'ma'asrot are given, no one's allowed to eat from it. When it comes to figs and wine, which we're going to discuss in this Mishnah, the Gemar Melacha for figs is when they're pressed into fig cakes. They were taken and smushed together in a press, turning them into cakes. Wine was considered fully processed when it was filtered and then eventually poured into barrels.
So we'll apply that to this Mishnah. If somebody had fig cakes that were already made, and therefore fully processed and obligated in terumot u'ma'asrot, and then they became separated, he hires workers to press the figs into cakes again. Or, let's say the wine was already in barrels, and somehow the barrels opened up, so he hires workers to reseal them. The workers are not allowed to eat the fig cakes or drink the wine while they're working, because these particular figs and wine were already fully processed; the Gemar Melacha had already taken place. A worker doesn't have the right to eat from food or drink that was already fully processed, even if it's there because it became undone. For example, the figs became unpressed and the wine barrel became open. That doesn't mean they now revert to their previous status. They were already complete, and therefore they remain complete and inedible to someone until terumot u'ma'asrot are eaten. The worker in this scenario is not allowed to eat from them because terumot u'ma'asrot have to be given, and he has no right to eat them because the food is fully processed.
But that's only if he hired them, informing them of the situation, the status of the food. If the employer did not tell the workers when he hired them that they would be working with food that was already fully processed, he has to separate terumot u'ma'asrot from the figs and the wine, and then give the workers some to eat. Even though workers are not usually entitled to eat processed food, these workers accepted the job with the assumption that they would be allowed to eat. They were told that they were going to barrel wine and press figs, so the assumption is that they would be doing that to food that had never been processed. Therefore, in the interim, until it was processed, they would be allowed to eat from it, and they accepted the job with that expectation. Therefore, if he never informed them, he has to provide them with food: he has to separate terumot u'ma'asrot, thus making the food edible to them, and then give them some to eat.