Luke 18:12 "I fast twice in the week, I give tithes of all that I possess." The context of this scripture is the parable of the Pharisee and the publican. It shows that by the New Testament times, tithing was paid with whatever they possessed--there is no qualification of its form.
The first mention of tithing is in the Old Testament when Abram paid tithing to the King of Salem, who was the high priest (Genesis 14:16-20) "And he brought back all the goods, and also brought again his brother Lot, and his goods, and the women also, and the people . . . And Melchizedek king of Salem brought forth bread and wine; and he was the priest of the most high God. And he blessed him, and said, Blessed be Abram of the most high God, possessor of heaven and earth. And blessed be the most high God, which hath delivered thine enemies into thy hand. And he gave him tithes of all."
The "tithes of all" references the "goods," or spoils of war that Abram and Lot brought back from Sodom and Gomorrah. The goods could have been anything including livestock, treasures, money. We know that "goods" does not reference food because in Gen. 14:11 (KJV) it says, "And they took all the goods of Sodom and Gomorrah, and all their victuals, and went their way." So this talks about goods and food being separate.