Hi John,
Yep, I meant the labs test the chymosin strength and dilute with water until it's to the right standard.
Dairyconnection, from what I recall, repackages rennet from a WI supplier that usually sells to the cheesemaking companies in WI. Their two vegetable double strength rennets differ in that one is certified organic.
Most vegetable rennet is usually the cheaper (compared to animal) M. Miehei-derived one. It doesn't matter practically what type of veg rennet you buy as they work the same way. It does matter what type of veal rennet you buy because they have varying levels of pepsin and other compounds. The variation comes from the age of the animal when the rennet is obtained from it. This is one factor that influences final flavor and why some people swear by animal rennet claiming it produces a better cheese.
Freeze dried rennet works similar to junket tablets. Chymosin strength is more like 1:100,000 for the dry powdered rennet. Not sure what it is for the junket tablets.
The products Renco makes are directly comparable to European and US products, but I am not sure of the concentration. European rennet is usually 1:10,000 for single strength.
All these differences mean it is vital to not buy too much rennet because it loses strength over time. Not more than you can use in 1-1.5 years. It is also vital to get the manufacturer's data for the proper addition rate and use a dropper or similar way to measure grams or ml exactly. Especially with double strength rennet, it is easy to add too much, which can result in bitterness. At least, that's what happened to me.
. Manufacturers will typically say use XX volume for YY lbs of milk. Using 8.5 lbs/gal milk, I calculate the proper volume per lb or gallon and then use that instead of the 1/4 teaspoon per gallon or similar inexact measurements. It really helps with producing repeatable results.
I have some more rennet details in my head for non-animal rennet, such as GMO vs non GMO, true coagulants made from vegetables, etc. But I have to run. I'll try to post later.