I think the instructions about using water, salt, and baking soda are often vague because people don't really know how they work.
The point of using water in rendering is to allow it to absorb some of the color and odor causing chemicals that may be present in the fat. Ideally you should do what you can to encourage the water and fat to mix together when rendering, so this separation process can happen efficiently. It's a good idea to stir the warm fat-water mixture frequently and/or allow the water to gently simmer so it will agitate the mixture on its own.
Baking soda as Lion Princess explained, will slowly saponify with any free fatty acids and react with some of the odor-causing organic chemicals. It's best to add the baking soda early on so it has time to do its job. It doesn't work quickly, unlike lye, but it's safe and effective.
Adding salt increases the difference in density between the fat and the water. Bigger density difference => faster separation. That's good in the cool down, but not as good when actually rendering. So my advice is to not add salt while actively rendering the fat. When you want to stop so the fat and water can separate and cool down, then add the salt and stir until it's dissolved. In traditional rendering, the salt is helpful but not strictly required.
***
After the first render which removes all of the cracklins (solids) is done, I've been experimenting with stick blending the fat and water together for the second and subsequent renders. The result of stick blending lard and water together is a semi-stable emulsion, which is definitely not a good thing. On the other hand, the high intensity mixing has the benefit of allowing the water to absorb as much of the water-soluble impurities as possible. In this case, I ~have~ to use salt to get this emulsion to "break" so the fat and water will separate.
CAUTION -- I'm sharing this idea in case someone wants to try this experiment themselves in the spirit of learning. Don't try this stick blending thing on a casual whim, because it can make a huge mess that you may or may not be able to easily fix. I may eventually decide the results are not worth the trouble, but I think it's worth doing a few experiments to figure that out!
The point of using water in rendering is to allow it to absorb some of the color and odor causing chemicals that may be present in the fat. Ideally you should do what you can to encourage the water and fat to mix together when rendering, so this separation process can happen efficiently. It's a good idea to stir the warm fat-water mixture frequently and/or allow the water to gently simmer so it will agitate the mixture on its own.
Baking soda as Lion Princess explained, will slowly saponify with any free fatty acids and react with some of the odor-causing organic chemicals. It's best to add the baking soda early on so it has time to do its job. It doesn't work quickly, unlike lye, but it's safe and effective.
Adding salt increases the difference in density between the fat and the water. Bigger density difference => faster separation. That's good in the cool down, but not as good when actually rendering. So my advice is to not add salt while actively rendering the fat. When you want to stop so the fat and water can separate and cool down, then add the salt and stir until it's dissolved. In traditional rendering, the salt is helpful but not strictly required.
***
After the first render which removes all of the cracklins (solids) is done, I've been experimenting with stick blending the fat and water together for the second and subsequent renders. The result of stick blending lard and water together is a semi-stable emulsion, which is definitely not a good thing. On the other hand, the high intensity mixing has the benefit of allowing the water to absorb as much of the water-soluble impurities as possible. In this case, I ~have~ to use salt to get this emulsion to "break" so the fat and water will separate.
CAUTION -- I'm sharing this idea in case someone wants to try this experiment themselves in the spirit of learning. Don't try this stick blending thing on a casual whim, because it can make a huge mess that you may or may not be able to easily fix. I may eventually decide the results are not worth the trouble, but I think it's worth doing a few experiments to figure that out!
