Causes of bitter fruit Common causes of stress that leads to bitter fruit include: extremely hot (or cold) temperatures. overly dry weather. sunburn damage.Click to see full answer. Similarly one may ask, what makes peaches taste bitter?You also could have soil that is too alkaline. That is so disappointing. When we had a peach tree at my grandmother’s house, the peaches were really bitter (and rock hard) the summer before the tree died. Unpruned trees often produce bitter fruit.Additionally, why are some fruits bitter? Some plants produce chemicals that are bitter and toxic because of attack by pests. Take, for example, cucumbers and musk melons. They are part of the Cucurbit family, along with squash. These plants naturally produce chemicals called cucurbitacins, which are very bitter, and in large quantities can make a person ill. Similarly, why are my peaches not sweet? If it is picked green, a peach will have a “green” taste to it and it will not be as sweet. While most peaches on your tree come into ripening around the same time, your earliest ripe fruit will be what gets the most sun exposure – the fruit at the ends of the branches.How do you know if Peaches have gone bad?Peaches that are spoiling will typically become very soft, develop dark spots and start to ooze; discard any peaches if mold appears or if the peaches have an off smell or appearance.