A “cooperative corporation” means a corporation composed of ultimate producers or consumers, or both, organized for the purpose of conducting any lawful business primarily for the mutual benefit of its shareholders who may be natural or legal persons, and the earnings, savings or benefits of which are used for the general welfare of the shareholders or patrons or are distributed in the form of cash, stock, evidences of indebtedness, goods, or services, proportionately and equitably among the persons for which it does business upon the basis of the amount of their transactions or participation in production, or both. However, any such corporation may pay out of its net surplus earnings, savings or benefits, not to exceed 5 percent interest upon its capital stock.