I recently found an old family cream pie recipe that called for scalding the milk. Is there any reason to do this other than to kill bacteria? If not, isn't this an unnecessary step if using pasteurized milk?
If you've found a very old recipe that calls for scalding for food safety reasons, then yes, it is probably unnecessary. However, there are places where it is called for.
In particular, when making Béchamel (which is made by combining milk and roux), it is important to scald or at least warm the milk, otherwise you can and most likely will end up with lumps. The reason to actually scald as oppose to simply warming the milk tends to be one of cooking time; the hotter the milk is, the less time you have to spend whisking.
In general, any recipe that calls for milk and needs to thicken tends to benefit from scalding for the latter reason - it just takes less time to thicken that way.
Wikipedia has also other uses for Scalded milk besides killing bacteria:
- Scalded milk is called for in the original recipes for béchamel sauce, to prevent the sauce from thickening excessively. Since these early recipes predate pasteurization, this was a necessary step.
- Scalded milk is used in bread to make a more tender loaf.
- Scalded milk is used in yogurt to make the proteins unfold. The acid produced during the yogurt development causes less whey separation and a firmer yogurt.
- Café au lait, baked milk, and ryazhenka also use scalded milk.
- Scalded milk is used in many doughnut recipes.
There's different types of pasteurization -- you can heat it up a lot, for a short period time, or hold it at a lower temperature for longer. Scalding the milk makes sure you denature the proteins, no matter the type of pasteurization used, which can affect how some breads rise, so in baking, if it calls for scalded milk, I still scald the milk.
In a cream pie recipe ... I'm not so sure if it was just a process to pasteurize, or if it might've served some other purpose. You could always try making two pies, one scalded, one not, and compare the differences.
(and, as I've said before -- I don't warm the milk for bechamel -- I just add the milk in small amounts at the beginning, stirring well after each addition, and I've never had problems with lumps ... it's the way my great grandmother taught me, and it keeps me from washing another pot ... I also use a wooden spatula, not a whisk, both because that's how I was taught, I can get into the corners, and I really hate cleaning whisks)
The reason I now scald my milk when making pies, custard and quiches: (I hope I can express this correctly) It isn't just about thickening the liquid or a jump start. I now scald my milk 20 to 30 minutes at 185 degrees F. I use a candy thermometer gently stirring all the while. This scalding process has made all the difference in my pies, custard and quiches. Something molecularly changes and binds... the proteins... I believe. It adds strength and stretchiness to the milk. Now I never have puddles of liquid in the bottom or on the top of my pies, custard and quiches. It isn't about evaporation or thickening. It is about changing its nature.