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The melakha of Kneading is defined as forming something new with characteristics that differ from those of its component parts. Neither flour nor water left on their own can rise or be baked. Only after they are mixed together can they be made into bread and baked goods. Similarly, dried earth or spackle on their own and water on its own cannot be used for building. Only after they are mixed together can they be used for construction. Whenever people mix a dry ingredient with a wet one to form a thick mixture, they have transgressed the prohibition of Kneading. Therefore, jello may not be made (by mixing gelatin powder with water), nor instant mashed potatoes (by mixing water into dehydrated potatoes).
On the Torah level, Kneading is limited to a thick mixture; creating a loose mixture which can be poured is not biblically prohibited. The rabbis prohibited this as well though, since people might mistakenly assume that if making a loose batter is permissible, making a thick one is too. Nevertheless, a loose mixture may be created if it is done with a shinui. One can change the order in which the ingredients are combined, as well as change how the stirring is done. For example, instead of stirring the batter with a circular motion, one may stir in straight lines, whether side to side or perpendicularly.
