How long should I marinate a piece of meat?

For marinades in recipes that call to marinate for a few hours or overnight, which is correct? V. Klestadt

Marinades increase flavour and tenderise flesh. This happens in two ways. Firstly, the marinade itself will often contain compounds that will break down muscles from the outside in. Acids such as lemon juice and vinegar denature the protein while enzymes in fruit such as kiwi and pineapple very quickly break down muscle. The second way comes from enzymes within the muscle. By covering flesh in liquid one is stopping airborne bugs getting into your food. Compounds in herbs and spices such as rosemary, garlic and paprika inhibit the growth of bad bugs. This bides time for the enzymes in the flesh to break down the proteins in the muscle fibres into amino acids giving the double whammy of both tenderising the flesh and giving your meal some extra umami kick. Smaller pieces of meat, chicken or fish need less time marinating so a few hours for chicken pieces for skewers on the barbecue will flavour them up, however, if you're cooking a great shoulder of lamb you might start the morning before and keep it in the fridge until the next day.

How do they make Greek yoghurts differ from others? R. Mischlewski

An Aegean sunrise, strong black coffee, figs, yoghurt, honey and a roaring hangover. I think many of us share similar memories of holidays in Greece. In Greece yoghurt is traditionally made with sheep's milk then strained to remove the whey. This style of yoghurt making is found across the Mediterranean, Middle East and India. This thick, nutrient-dense paste with much moisture and lactose removed was more stable in a warm world prior to refrigeration. It handles heating well and tends not to split when used. Pot set yoghurt is made by adding bacterial cultures to warmed milk that then curdles the milk creating the curd and the whey, the thin watery liquid on top of the curd. Then there are some dairy products that could be argued are not really yoghurt at all. These are thickened with gelatin and gum stabilisers and often sweetened with man-made chemicals. These make up the vast majority of yoghurts in the supermarket.

What is the best way to wash fruit and vegetables, particularly berries? J. Brogan

I once was working in a kitchen in Mexico and the chef instructed me to wash some salad leaves. He handed me the lettuce, a bowl and detergent. In that part of the country the groundwater was so badly polluted that the vegetables had to be washed in a special cleanser to make the veg safe to eat. Thankfully we look after our environment a little bit better over here but you want to remove field dirt, dust and other matter before cooking. As a rule the harder the skin the harder the washing. Ground dwelling veg generally have developed hard skins to protect against insect and nematode attacks underground and should be given a thorough scrubbing to remove dirt from around eyes and folds in the skin. Leafy greens can be washed in cold water then spun dry in a salad spinner or folded into a clean tea towel that is spun around – preferably outside. Berries, with their soft skins need to be treated tenderly. Wash strawberries before removing stems so they don't absorb water. Pat dry with a clean tea towel. Place raspberries and blackberries in a colander then float in water. Drain and drain further on a tea towel.

How do I keep my potatoes firm for potato salad? D. Keith

If you slowly bring your potatoes to just under 60°C in a pot of water and hold the temperature there for around 20 minutes you can create firm cooked potatoes. By doing so you're activating an enzyme in the cell walls that changes the way calcium ions effect the pectin. Pectin is the starch that gives fruit and vegetables their rigidity and this process makes it more stable at higher temperatures. After this slow, low heat treatment the potatoes should remain firmer when cooked in the normal manner afterwards. Once cooked dress the potatoes shortly before serving so they don't absorb the dressing and soften.

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