How the sweetness of an apple and sourness of a lemon derives from the Sefiros:^[1]

Ever wonder why an apple is sweet while a lemon is sour? Is there actual sweetness in the earth and ground that causes the apple to be sweet? Now, it is known that every creation contains a Mazal which instructs it to grow. However, one cannot say that it is the Mazal which is responsible for its sweetness, as certainly a Mazal does not have any relation with such matters. Rather, the explanation is as follows: The sweetness of the apple comes from the divine attribute of Chesed, while the bitterness or sourness of a food comes from the attribute of Gevura. Now, the attributes of Chesed and Gevura themselves are spiritual and have no relation to physical taste. Nonetheless, through a chainlike descent of their Divine light throughout the various worlds from one level to another, their revelation eventually becomes transformed to a corporeal entity of actual sweetness, and it is hence found that actual sweetness derives from the attribute of Chesed. Now, although physical sweetness has no relation at all to the attribute of Chesed, nonetheless, it does share similar qualities to all of the various types of spiritual pleasures that exist and derive from Chesed. For example, there exists pleasure and sweetness in intellectual discovery, and there exists pleasure and sweetness in a song. Accordingly, through a chainlike descent this spiritual sweetness can eventually become transformed to an actual physical sweetness, even though there is a great distance and difference between them.

[1] Torah Or p. 13b