Under Federal Orders, what varies between classes of milk?

The correct choice highlights that prices paid to producers can vary between different classes of milk under Federal Orders. Federal Milk Marketing Orders regulate the purchasing and pricing of milk in the United States, and they categorize milk into different classes based on its end use. For instance, Class I milk is fluid milk used for drinking, while Class II milk is used for soft products like yogurt and ice cream. Each class has its specific pricing formula, influenced by factors such as supply and demand, processing costs, and market conditions, which leads to distinct prices being set for each class.

This pricing structure ensures that milk producers receive payment reflective of the market value of their product based on how it will ultimately be used. This incentivizes producers to maintain quality and invest in production methods to meet the demands of each class.

The other options, while relevant to milk production and processing, do not capture the variability in price across classes. For example, fat content is a characteristic of milk that contributes to its classification, but it does not directly relate to the payment structure for producers. Similarly, type of packaging and production methods may differ across products but are not factors that determine pricing variations among classes under Federal Orders.