Finely chopping onions significantly reduces cooking time because the smaller pieces break down faster and release their moisture and flavor more quickly. This results in a quicker softening and caramelization process.
The size of onion pieces directly impacts how long it takes for them to cook. When onions are finely chopped, more of their surface area is exposed to heat. This increased exposure accelerates the breakdown of the onion's cell walls, releasing sugars and moisture. This process is crucial for softening the onions and developing their characteristic sweet flavor. Larger onion pieces, on the other hand, have less surface area exposed, requiring more time and heat to achieve the same level of doneness. The finer the chop, the faster the onions will cook down and integrate into the dish. This is particularly important in recipes where a smooth texture or quick cooking time is desired, such as sauces, soups, or stir-fries.
Be careful not to burn finely chopped onions, as they cook much faster. Keep the heat at medium or medium-low and stir frequently to ensure even cooking and prevent scorching.