How long can milk be stored in the refrigerator after boiled and put in a Ball jar? I've finally gotten my steel-cut oats recipe nearly perfect and I'm trying to figure out how long I can store them (so I know how much I can make at once). Basically I'm doing a double-boiler setup in a ball jar cooking the oats for 45 minutes to an hour and then putting on the lid and then refrigerating for later use. 

Normally milk will go bad after a couple weeks in the fridge but I assume boiling and vacuum sealing will extend this time. I'm not really familiar with canning though so my assumption might be wrong. 

How long should I expect milk to last in the fridge when boiled and sealed in a Ball jar?
Unless you are using a canning method that is actually designed for long term storage and shelf stability, you cannot assume the food is sterilized or pasteurized by home processing methods.  

You should therefore not expect a refrigerated shelf life of more than 2-3 days, the same as if you had not processed it.

Finally, you are creating a low acid food with absolutely no protection (other than refrigeration) against botulism, so you definitely do not want to store it more than this guideline.

In addition to botulism which is not detectable by odor or taste, if you do see unusual appearance, especially bubbling, or detect an off odor or flavor, you should definitely discard.