Ok, I know people have done this for years with sourdough, and I can understand wanting to cultivate the growth of bacterias, is this safe though? Recipe from "500 Low-Carb Recipes" by: Dana Carpender

Yogurt
1 Tablespoon Plain Yogurt
1 1/2 to 2 cups instant dry milk

1. Fill a clean, 1-quart, snap-top container half full with water.
2. Put the plain yogurt in the water, and stir. Add the powdered milk, and whisk until the lumps are gone.

*For your first batch, you'll use store-bought plain yogurt as a starter, but after that you can use a spoonfull from the pervious bath. Every so often it's good to start over with fresh, store-bought yogurt, though.

3. Fill the container to the top with water, whisk it one last time, and put the lid on.
4. Put your yogurt-to-be in a warm place. I use a bowel lined with an old electric heatingpad set on low, but any warm spot will do, such as inside an old-fashioed gas oven with piolet light, on the stove top directly over piolet light, or even near a heat register in winter.
5. Let your yogurt sit for 12 hours or so. It should be thick and creamy by then, but if it's still a little thin, give it a few more hours. When it's ready, stick it in the refrigerator and use it just like store-bought plain yogurt. Or flavor it with vanilla or lemon extract and some splenda or stevia.

I thought this sounded cheaper and would be lowe rin carbs. Dry whole milk is more expencive and harder to find though then low-fat. Would this be safe, or would I have to worry about it sitting out and other types of bacterias and such forming?