Corned Beef for 40 - how many lbs?
It depends on the ages of the non 3 year old children, but it sounds like you have the equivalent of about 30 adults.
Of the 25 adults, what's the female/male breakdown? Out of that 25 do you have elderly guests? Any vegetarians?
Are these light eaters or heavy eaters? Do they like corned beef?
Do you want leftovers?
What time are you serving the meal? Is it a sit down dinner? Will alcohol be served?
I lose half of the weight, possibly even more when I cook corned beef. Corned beef is one of those cuts that favors long slow cooking. In other words, it's one of those cuts that want to cook past the point of doneness. By the time you cooked it long enough to be succulent, there's not much left.
If you know you have light eaters or a lot of women, I'd go with 4 ounces per person, 8 ounces pre-cooked weight. That's 15 lb.
If these are hearty eaters, then I'd go closer to 8 ounces per person, one lb. pre-cooked weight. That's 30 lb.
That's the normal range of cooked protein per person- 4 to 8 ounces. Corn beef has one important aspect that differentiates it from other forms of protein- it has a tendency to be very salty. The more salt your guests consume, the more water they will drink, they less food they will eat. In recent years corn beef has gotten saltier, so much more so, that it's almost impalatable. I would break out a big cooler and soak your corn beef in ice water for a couple of days to get some of the salt out. If you don't soak it, I'd cut your allowance by 1/3 to allow for the extra water being consumed. I'd also cross your fingers that it doesn't end up too salty to eat. That would leave you with a lot of corned beef on your hands.
Soaking and low slow cooking are essential for making the best corned beef. It won't work with 30 lbs. but a pressure cooker is ideal.
Even split between men and women. Most kids are 6 or under, so planning for 30 adults is about right.
This is at dinner, to be served with much Guinness.
I have about 19 lb on hand right now, that falls in your range. I think it may be adequate since I'll also have the other fish and meat dishes, in addition to crudites/cheese/etc.
I will be making a vat of green trader joes mac n cheese for the kids.