A chef might refrigerate an ingredient slightly before dicing to firm it up, making it easier and safer to cut precisely, and to minimize bruising or damage to delicate items.
Refrigerating an ingredient before dicing offers several benefits. First, chilling firms up the ingredient's texture. This is especially helpful for soft or delicate items like tomatoes, onions, or certain cheeses. A firmer texture allows for cleaner, more precise cuts, reducing the likelihood of crushing or tearing the ingredient. Second, chilling can make the dicing process safer. A firm grip is easier to maintain on a chilled ingredient, reducing the risk of the knife slipping. Finally, for some ingredients, like onions, chilling can help reduce the release of irritating compounds, minimizing tearing while cutting. The slight chill doesn't significantly alter the ingredient's flavor or cooking properties, but it greatly improves the dicing process.
Don't over-chill the ingredient! Freezing or excessively chilling can damage the texture and make it difficult to work with. Aim for a brief period in the refrigerator, just long enough to firm it up slightly.