I was taught the idea that if you let frozen meat thaw out over night then it is better for the end product that defrosting it in the microwave? Does this have merit or is it just an old wives tale?
Also does cooking frozen meat effect the taste or will it just take longer to cook?
Microwaving meat to defrost it tends to start cooking it at the edges and generally make it go weird and rubbery (scientific terms I know). So yes, it is better to defrost 'naturally' in the fridge, in terms of quality.
Freezing damages meat by bursting the cell walls as their water expands. This affects the texture more than the flavour. The damage is done when freezing, not cooking from frozen, so the latter should not effect taste. The main issue with cooking from frozen is that if the item is big (say, a roasting joint), the outside can be overdone by the time the middle gets up to a safe temperature.
Defrosting in the fridge is typically better than thawing in the microwave ... but not if the item is still frozen by the time you want to cook it. (eg, large whole poultry may take more than a day to thaw)
The issue is that you want to minimize the potential to cook the item being defrosted, so you don't want to thaw it using too hot of a thawing method. You also don't want to leave many foods for too long in the food 'danger zone' (40°F to 140°F / 4°C to 60°C) for too long.
If the item to be thawed is wrapped in plastic (or will fit in a zip-top bag (make sure to remove most of the air)) we can use methods such as running cold water baths (place food item in a container, add something to weight it down, place container in water, run a trickle of cold water into the container). The increased thermal mass of the water vs. air allows us to thaw the item more quickly than we'd get from puttng it in the fridge.
Also note that in cases like steak, it may be better to cook from frozen, assuming care was taken when freezing it.
I prefer meat thawed in the fridge over the course of a couple of days to microwave defrosting. As previously said, the microwave cooks the edges, but it also seems to release juices and fat from the meat, hence making the meat a little tougher in my opinion, including ground meat.
In addition, if you are thawing ground meat for patties, they will NOT bind well after microwave thawing due to the melted fat throughout the meat. If I am in a rush, I will shorten the defrost in microwave, and then refrigerate in order for the ground meat to set or become firm (coagulate, what a great word) for easier handling for making patties.
Absolutely. Most microwaves defrost unevenly.
On the other hand, there are a couple faster ways to defrost other than letting it sit on the counter. Further, it is in fact even better to let meat defrost more quickly, because meat left out will allow bacteria to grow, which is a further concern.
One tip is to let a frozen food rest in warm water while sealed in a waterproof bag of some sort. This will significantly decrease defrosting time.
The old wives' tale was based off the presumption that letting it sit out is the only way to defrost evenly. It does hold some grain of truth, as quickly defrosting an item runs a chance of the inside not defrosting all the way. However, due to the distribution of temperature, if you let a frozen item sit in water (while in a waterproof bag), the temperature will eventually even out, defrosting it all the way to the core.
Defrosting in the microwave just doesn't work properly. Ice hardly absorbs any microwaves, compared to liquid water. So microwaving heats the already unfrozen parts while the frozen parts only get affected indirectly. So it doesn't speed up things very much, costs lots of energy and spoils the meat as mentioned by other answers.
But this is an effect of the microwave more then the speed.
If you want to speed up defrosting, put the meat in a plastic bag and put it in warm water. I have never heard of any negative effect taste or quality wise.
It's probably even more hygienic, because those little critters that live in your meat until you cook it will start to reproduce once, they are unfrozen. So you want to have the time during which the meat is only half frozen as short as possible.
