Peeling garlic after crushing it can result in a purer, less bitter flavor because crushing releases enzymes that create allicin, which then breaks down into other compounds. Peeling after crushing allows some of these harsher compounds to dissipate before cooking.
When you crush garlic, you rupture its cells, releasing an enzyme called alliinase. This enzyme interacts with alliin, a sulfur-containing compound also present in garlic, to produce allicin. Allicin is responsible for garlic's pungent aroma and flavor. However, allicin is unstable and quickly breaks down into a variety of other sulfur-containing compounds. Some of these compounds contribute to a more intense, sometimes bitter, flavor.
Peeling the garlic clove *after* crushing it allows some of these volatile, harsher-tasting compounds to dissipate into the air before you cook the garlic. This results in a milder, sweeter, and arguably 'purer' garlic flavor in your dish. If you peel the garlic *before* crushing, you're essentially trapping all those compounds inside the garlic, leading to a more intense and potentially bitter taste when cooked. The difference is subtle, but noticeable, especially in dishes where garlic is a prominent flavor.
For the mildest garlic flavor, crush the garlic, let it sit for about 10 minutes after peeling, and then add it to your dish towards the end of the cooking process. This maximizes the dissipation of harsh compounds and prevents burning, which can also contribute to bitterness.