Garlic

Choosing

Pick heads that feel firm and heavy. If it gives under pressure, or the skin is loose over the cloves, it has dried out. Green sprouts are edible but bitter — cut them out.

How you cut it decides the flavour

Cutting garlic ruptures cells and forms allicin. The finer the cut, the more cells break and the sharper and more pungent it gets.

• Whole cloves — mildest, keeps its sweetness. Samgyetang, Gambas al Ajillo.
• Sliced — aromatic without much bite. Aglio e Olio.
• Minced — much stronger. Stir-fry marinades, Jeyuk Bokkeum.
• Grated or crushed — the sharpest. For raw sauces.

Temperature gives you three different ingredients

Gently warmed it is sweet and mild; browned over medium heat it turns nutty; burnt it is irreversibly bitter. That is why browning the garlic in Aglio e Olio counts as a failure. More in Blooming spices.

Storing

• Whole heads — room temperature with air movement. The fridge encourages sprouting.
• Peeled cloves — sealed, refrigerated, two weeks.
• Minced — one week refrigerated; frozen in an ice tray, three months. This is standard practice in Korean kitchens.
• Garlic stored in oil is a botulism risk at room temperature. Refrigerate it and use it within a week.

Substitutes

Garlic powder points in a different direction — it has none of raw garlic's pungency. Reckon one clove ≈ 1/8 tsp powder, but where garlic is the point, there is no real substitute.