This is basically the method I use when cooking steaks. Also see this post which discusses the effects of flip intervals on cooking time and evenness of steaks: http://news.ycombinator.com/item?id=1117296 Also, some other simple tips: 1) In general, the more marbling the better. You want lots of veins of fat in the muscle of the cut. Big chunks of fat don't count, and leaner meat won't have as much flavor. 2) Hard wh…
My mum came along for a trip to the market a few weekends ago and had me looking for well aged porterhouse. She told me to look specifically for the yellowing fat as its a sign of age. She grabbed one that looked sickeningly yellow but I can confirm that this was one of the most tender porterhouses I've had.
1) The animal was old.
2) Worst case: the animal was losing weight when it died. This will make the meat taste sour (as best I can describe).
3) Best case: it's grass fed and not grain finished. This fat will usually be hard. If you're in the UK (guessing because you said "mum"), that's probably what you got.
4) It's dry aged beef. The outer layer will turn a bit yellow, but otherwise the fat is going to be whatever color it was before aging. Temperature and duration of aging has a lot more to do with how tender the cut is going to be.
Really, it's the spongy feeling stuff you want to avoid. If you're in the US, and it's not marketed as grass fed, it's almost certainly from an old dairy cow or an animal which was sick when it was slaughtered (and losing weight).