Leeks belong to the onion family and look a bit like a huge spring onion, with a mild onion flavour. They can be used as a mild alternative to onions in many dishes and come with the benefit of not causing tears.
Good quality leeks are firm and smooth, free of blemishes, and have white stems with dark green leaves. The cut bottoms should be flat; rounded may indicate prolonged storage.
Postharvest storage temperature
Hydro-cooling, crushed ice, and vacuum-cooling are the most common methods to promptly cool harvested leeks to 0°C. Good refrigeration retards elongation and curvature that develops in leeks at 10–21°C. Yellowing also develops more rapidly at warmer temperatures. Leeks can be stored for 2–3 months at 0°C with 95–100% relative humidity. Leeks are not sensitive to chilling temperatures and should be stored as cold as possible without freezing.
Controlled atmosphere storage
Storage for 4–5 months at 0°C is possible with controlled atmospheres, although there will be some loss of quality. Recommended controlled atmosphere conditions are 1–3% O2 and either 2–5% CO2 or 5–10% CO2. Such controlled atmosphere retards yellowing and decay development. Levels of 15–20% CO2 cause tissue injury.
Leeks produce very low levels of ethylene and are moderately sensitive to it. Detrimental effects include softening and increased decay.
High relative humidity (95–100%) is essential to prevent wilting. Moderate wilting is apparent when leeks lose about 15% of their weight.
Disease & infection
Most diseases that attack onions may also affect leeks.
Trim leeks roughly 5cm from leafy end and 1cm from the base, then slice the whole length. For best flavour, allow sliced leeks to sit for at least 5 minutes before cooking.