Beef – Substitution for Suet in Christmas Pudding

Tallow does not need to be refrigerated and can last a year or longer. I would not worry greatly about decomposition, but oxidation can be a problem. Make sure to store it in an airtight container and you shouldn't have a problem.

It depends on what you need the tallow for and whether you want it to taste significantly of beef or not, water rendering will give a cleaner tallow.

With 100lbs of tallow, your main limiting factor is driving off all the water. Tallow is about 75% fat, 22% water and 3% protein so you basically need to boil off 22 pints of water. What heat sources do you have that's going to most efficiently boil off 22 pints of water?

Here's what I would recommend: chop about 1 - 2 lbs of the tallow into 1/2 inch sized pieces to start off with and start them rendering in a pan on the biggest burner you have set as high as possible. Place a thermometer in there and monitor when it reaches 250F, making sure to keep the bottom of the pot scrupulously clean of stuck on bits (if there are stuck on bits, transfer to another pot so that the bottom stays clean).

When it reaches 250F, add in another batch of tallow pieces too cool down the pot and wait until it gets back up to temp again. Repeat until all the tallow is rendered.

This process can be parallelized with multiple pots and thermometers if so desired. The more heat you can apply, the faster this will go.