How do you 'notice' when the brine hasn't reached certain areas?
Its easy to see if the brine is working and you're possibly just overcooking - weigh the bird pre and post brine, before cooking. If it weighs more, you've got the liquid.
A properly brined bird shouldn't taste like 'omg, thats salty!'. I think two things are going on here:
Your expectations may be off. Brining isn't magic. It just gives you more liquid in the bird so that when you cook some out there's more at the end. (It can enhance flavor if you add herbs & spices to the brine also).
You may just be overcooking the chicken. If you overcook it enough, the brine will appear to have done nothing - you've just cooked out all the juiciness you put it. Use a meat thermometer and make sure its 'just right'.
Brining definitely works though, and it shouldn't be overly bird specific.
It's down to what the chicken ate while it was alive. Saturated fat sets, olive oil sets if you chill it, but not otherwise, and a number of seed oils do not set (rapeseed for instance). When you make a stock which has solidified fat on top, that's saturated fat, so I'd hazard a guess that the stock where the fat doesn't set means a healthier eating chicken, because it contained less saturated fat to start with.
UPDATE: Thank you to the person who bothered to do the research and said my answer 'might have some merit'. Chickens are no different from human beings - the fats you put in are the fats floating round your bloodstream and depositing in various places; think about corn fed chickens, where the fat composition is slightly different, not to mention the colour of the flesh itself. That will be a partial explanation; when taken together with the fact that not all chickens, even in the same flock or brood, get to eat the same diet, because the pecking order dictates that some free range birds don't always get the pick of the food, explains differences in chickens from the same supplier. Of course, if you can come up with another explanation, I'd be delighted to hear it...
UPDATE 2: Perhaps I should have been clearer. I am not for a moment suggesting that the fats eaten are deposited in their original form, but if you know anything about biology (chickens or otherwise) then you'll know that certain synergies occur, depending what's put in, which change the composition of any fats deposited within the body system. Hence the connection between eating lots of saturated fat and having high cholesterol in humans, for example.
UPDATE 3: Rumtscho: Can't find any scientific evidence so far to prove this theory regarding chickens, but, for interest's sake, and to prove how much of a difference it can make, farmed salmon in Britain no longer has a balanced omega 3/6/9 ratio, as it should do, and still does in the wild. It's because the feed had to be changed, and the consequence of that has been a much higher level of omega 6 in particular. I'm still looking for something on chicken.
UPDATE 4: Now I've had time to look properly, it's not at all difficult to find scientific evidence, there's plenty of it. There's a study carried out by The American Society for Nutritional Science in 2000 comparing the fat deposition (and other metabolic processes) between chickens fed the same diet, but one lot with saturated fat included in the form of tallow, and the other lot with polyunsaturated fats. The fat deposition in the birds fed tallow was greater, and the composition of the fat contained more saturates compared to the polyunsaturated group. These results reflect previous studies (Sanz et al 1999 and 2000).
Effectively, it's like everything else - you get back what you put in.
Best Answer
Taken out of context, that doesn't make much sense, but I can think of several similar claims you might have heard - all of which are true and most can be found on the USDA fact sheet and the sites of most other agencies:
Perishable food should not be left in the "danger zone" (4.4° C - 60° C or 40° F to 140° F) (room temperature) for more than a total of 2 hours; 1 hour if the temperature is above 32° C / 90° F (mouth/gut temperature).
Freezing does not reset this countdown, it only stops it temporarily. Thus, it is not a safe practice to thaw and refreeze food several times (especially if it's being brought above refrigerator temperatures).
Cooking does reset the countdown, but unless you are in a completely sterile environment (hint: you aren't), you still have to keep food out of the danger zone after cooking, which is why guidelines say to refrigerate within 2 hours.
Most people reheat their food to "warm" or even "hot" but not cooking temperature. Unless you reheat to an internal temperature of 74° C / 165° F, then all that time in the danger zone after cooking is cumulative. So if you do what most people do and reheat food to 40°-50° C, a nice comfortable eating temperature, then you'd better either (a) only reheat the portion you plan to eat, and/or (b) throw out any uneaten portion instead of putting it back in the fridge.
Really it's all about the cumulative amount of time, since being fully cooked, that the food has spent in the danger zone. Theoretically, if you boiled the same piece of chicken every 12 hours and quick-froze it immediately afterward, it would stay safe indefinitely. It would also have no flavour or texture left, so I don't recommend it.
Since most people don't carefully measure the internal temperature of food when they reheat it, we have the "best practice" of only reheating perishable food once after it's been cooked, because otherwise it gets really hard to estimate how much time is left on that metaphorical clock. And, obviously, don't leave it in the fridge for more than a few days, because it can still spoil in there, just slower.