Sforno on Genesis 43:34/ספורנו על בראשית מ״ג:ל״ד

1ותרב משאת בנימין, to see if the brothers would display signs of jealousy.

2חמש ידות, five fold; the brothers would be served one serving each for every two of them, whereas Binyamin was given a portion equal in size to the portions served to each set of two brothers. This was Joseph’s way of showing that he considered Binyamin as equal to all of them combined. [the author was at pains to justify why Joseph gave Binyamin five times as much, not 4 times or 6 times, for instance. Ed.]

3וישכרו עמו, they were being served the kind of wines drunk by Royalty, something they were not used to, so that it made them drunk. They were careless in not leaving over some of the first kind of wine served them as was the custom for anyone invited to dine with Royalty. Compare Proverbs 23,1 כי תשב ללחום את מושל בין תבין את אשר לפניך, “when you sit down to dine with a ruler, consider well who is before you.”