Use Stainless Steel
Fruits and vegetables are very affected by their environment, and tomatoes are no exception. Using anything other than stainless steel when canning can actually affect the taste of the end product. The acid in the tomato may react negatively to metals like aluminum and copper, and you could end up with some discoloration or bitter taste. Wooden spatulas should also be avoided because they can carry over flavors from other foods and affect the taste.