We have seen that the Mishna (87a-b) teaches that a farm worker in the fields is permitted to eat as he harvests or performs other work. Our Gemara quotes a baraita that teaches that the employer can offer food or drink to the workers before they begin the harvest in order to limit the amount that they eat; similarly the workers can bring an appetizer to eat that will help them consume a large amount of fruit.
The question that our Gemara poses is whether the worker can roast the fruit in order to make it tastier when he eats. Although there are a number of baraitot that the Gemara quotes that seem to prohibit this kind of preparation, the Gemara rejects them as proof, arguing that it may not be intrinsically forbidden to roast the fruit, rather this may be a problem of bittul melakha – that an employee is not allowed to take time off from his work in order to prepare the fruit that he is permitted to eat. Thus, if a worker comes to the field with his wife or his children who are not working, perhaps he would be permitted to pick a fruit intending to eat it himself – a right expressly granted to him by the Torah – and hand it to his wife or to his child to prepare for him. The Gemara does not succeed in finding a decisive proof to resolve this question.
According to the Rambam, if a worker who was hired to harvest a field takes time off from his work to prepare fruit that he picked by roasting it, for example, not only is he stealing time from his employer, but he also is stealing the fruit, since he is only allowed to eat while he is working. Once he stops harvesting, he loses his right to eat from the fruit.