When Nebuchadnezzar conquered Israel and took Daniel and other Jewish men into his court, he assigned them food and wine from the king's table.
The king appointed for them a daily ration from the king’s choice food and from the wine which he drank, and appointed that they should be educated three years, at the end of which they were to enter the king’s personal service. Daniel 1:5 NASB
However, Daniel seems to believe it would be wrong for him to eat this, but eating vegetables and water is, somehow, alright.
But Daniel made up his mind that he would not defile himself with the king’s choice food or with the wine which he drank; so he sought permission from the commander of the officials that he might not defile himself. Daniel 1:8 NASB
“Please test your servants for ten days, and let us be given some vegetables to eat and water to drink. Daniel 1:12 NASB
So, what was it about the food and what was it about the wine that made Daniel believe it was inappropriate to eat?