Now that cold and flu season is upon us (trust me - this year, it's a doosie), it seems a good time to jump back into the kitchen to make something homemade and comforting. It's also a good opportunity to see how germs (bacteria) can actually be helpful rather than harmful. This experiment is to make your very own butter in your kitchen. All you need is 250 ml of heavy cream, a jar and some water. Let your cream sit at room temperature overnight, and then refrigerate it again in the morning. Once it's cool, pour it into a jar, put on the top and give it a good, solid shake - then keep on shaking. The goal isn't to shake the jar quickly like a paint-shaker, but to give firm, regular shakes in one direction - like your ketchup bottle is running out (you can use a food processor for a less intense work out!). After a couple of minutes, you'll notice that something is clearly forming in the bottom of your jar: butter! Pour off the liquid (which is buttermilk), shake a bit more with some fresh, cold water, and pour the liquid back off. The remaining solid is butter. Butter is a fat that occurs naturally in mammalian milk - cow, goat, etc. - and exists in some quantity in most types of milk (for example 1% milk is 1% butter fat by mass). The fat is trapped in little bubbles so that it doesn't separate, and by shaking, you've done two things to break those bubbles. First, letting the cream sit at room temperature allowed bacteria (which normally is not desirable) to grow and produce lactic acid, breaking some of the bubbles. Shaking the cream smacks the bits of freed butter fat around, breaking more bubbles and freeing more butter, which feeds a nice loop of butter-churning goodness. Your butter will not likely be very yellow: the yellow colour of butter comes naturally from beta carotene that animals get from grass.  Dairies that use grain-fed cows add the beta carotene directly into their butter to colour it. Goat's butter is naturally white: goats turn beta carotene into vitamin A. We hope you like learning about the good things bacteria can do. But, be sure to come to Discovery Centre while our popular Grossology: The Impolite Science of the Human Body exhibit is still here so you can also learn about some of the other things bacteria does to our bodies, and why it can make us sick. Grossology is on now until May.   For more great things to discover - visit the Discovery Centre on Barrington Street in Halifax, check out their website  or join them on facebook.      ...