Mincing produce extensively can create a paste because the cell walls break down, releasing moisture and starches that bind the mixture together. The friction and pressure from the mincing process also contribute to this breakdown.
When you mince produce, you're essentially cutting it into very small pieces. However, with prolonged mincing, several things happen at a microscopic level that lead to a paste-like consistency. First, the cell walls of the plant material rupture. These cell walls contain water and starches. As they break, the water is released, and the starches become available to bind with the water. Second, the mechanical action of mincing generates friction and pressure. This further damages the cell structure and helps to release even more moisture and starches. Finally, some produce, like garlic or ginger, naturally contain compounds that, when released through mincing, act as emulsifiers or binders, contributing to the pasty texture. The combination of released moisture, starches, and natural binders results in a paste rather than distinct, finely chopped pieces.
To avoid a paste, especially when using a food processor, pulse the produce in short bursts rather than running it continuously. This gives you more control over the final texture and prevents over-processing.