I worked for many years in many different restaurants and
commercial kitchens. Early in my career I would ask how long something should cook, and the answer would invariably be "Until it is done" usually
accompanied by an impatient and withering look from the chef or fellow cook
whom I had asked. I soon stopped asking the question. I also stopped asking for measuring
cups and - for this I got the most annoyed look in my cooking career - asking for measuring spoons. And I asked the question about the spoons just that one time.
Seriously, though...I think the better question is "How do I know when a meatloaf is done?"
There are two main ways of telling when just about any meat is done. If you pierce it with a fork, and the juices run clear...it is done. I don't like to do that. If it is not close enough to being done when you pierce the
meat, too much of the juice runs out and you are left with dry meatloaf and a Mother-in-Law who will never let you forget it. :-) A little safer method is to stick a toothpick into the meatloaf. If the toothpick comes out clean, it's done.
The best way is to use an accurate cooking thermometer, but don't insert it at the beginning. Let the meatloaf bake at about 350F for a while, about 1/2 hour, and check it.
Give the pan a half-turn and let it go for another 15 minutes or so.
Check it again.
When it is starting to get nice and dark brown on the top, that’s a good time for the thermometer.
Stick it into the thickest point of the meatloaf.
Let the needle come to a stop, and see what it says.
For an all-beef loaf, you are looking for an internal temperature of 125-130F.
For a combination beef, turkey, pork meatloaf, go for a temperature of about 150F.
And remember the most important rule of all: Don't cut any meat right out of the oven. Let it rest for about 10 minutes. This lets the juices settle back into the meat. If you start carving straightaway, you will again find yourself in that dry meat situation. Also, the heat of the meat itself will continue the cooking process while the meatloaf is resting, so you will notice an increase in temperature of as much as 5 degrees.
My meatloaf pan is made of glass; I can see through it. When I see the juices that the meatloaf has given off start to boil, I know it’s getting close to being done.
Hope this helped.