You probably learned at a young age to put the milk away promptly and in the coldest place in the fridge. So if somebody told you to leave the milk out in 100°F weather and actually eat what you got the next day, I can understand why you'd be squeamish. Especially if they told you they'd added bacteria to said milk.
Of course, if you've ever eaten yogurt, that's exactly what you're doing. To make yogurt, you basically add bacteria to milk and then let it incubate at a bacteria friendly 100-110°F. Gross.
Really, though, there's nothing gross about it! The bacteria you add are no more harmful than the yeast you add to bread or the dust mites that sleep in your pillow. (Less harmful if you have allergies!!) Here's what happens:
At around 110°F, the bacteria you add are in full activity--like tourists on a summer beach. They eat up all of the lactose in the milk, a form of sugar that many people can't digest, and produce lactic acid, the same thing that makes your muscles burn when you work out.
Just like lactic acid makes your muscles uncomfortable, it also makes the yogurt uncomfortable--for other bacteria, that is! The high acidity that makes yogurt a little bit tangy discourages the growth of the bacteria that make us sick. It also makes the milk curdle and form a jelly-like matrix of coagulated protein molecules. (The same thing happens if you add vinegar to milk!)
The first yogurts were made by just leaving milk out someplace where it could "catch" good bacteria (much the same way we catch colds!). These days, most people give the milk a push in the right direction by adding some good bacteria (in the form of already-made yogurt) at the start of incubation.
I've already posted on how to make homemade yogurt, but I thought I'd give you a few added benefits of making homemade yogurt:
1. Vitamin D
Lots of research has been done to show the benefits of vitamin D, particularly in aiding absorption of calcium. Unfortunately, most store-bought yogurts don't have vitamin D! Well, when you make your own yogurt, you choose the milk that goes into it, which means you can choose yogurt with vitamin D (and vitamin A) added.
2. Along those lines, you know everything that goes into your yogurt.
A lot of yogurts contain thickeners, like cornstarch or gelatin (watch out vegetarians!), artificial sweeteners and a lot of sugar. You may be okay eating those things, you may not. Personally, many artificial sweeteners give me stomaches and severe bloating so I avoid them. I'd also rather eat a yogurt that was thickened naturally from its wealth of good bacteria, rather than yogurt thickened with gelatin.
3. Not only can you choose ingredients, you can choose the outcome!
In yogurt, two things matter most: consistency and tartness. To make thicker yogurt you can do three things:
- Heat your milk to 185°F before incubating. The heat makes it easier for the acids to curdle the milk by breaking down some of the protein structure
- Add nonfat dry milk. This gives your milk more protein to coagulate, although some people don't like the taste and it can be a little bit tricky to add.
- Incubate for longer. This allows the good bacteria to produce more lactic acid, making sure all of your proteins get fully coagulated.
To change the tartness of the yogurt, you can do two things:
- Change your incubation time. Longer incubation = more acid = more tart. Shorter incubation = less acid = less tart. Of course, there will be textural repercussions.
- Change your starter yogurt. Each starter yogurt contains a different mix of good bacteria that curdle the milk in slightly different ways. D and I have found that Greek yogurts produce very little tang even after an 8 hour incubation, while Brown Cow and Stonyfield came out very tangy indeed.
4. It's way cheaper than store-bought yogurt.
In the long run, the cost of the yogurt input becomes negligible if you reuse your starter, it comes down to a simple equation: the price of homemade yogurt = the price of milk. And milk is pretty cheap.
Even if you're disorganized and buy yogurt every time you make a new batch, you're still only using 1-2 tablespoons of your store-bought yogurt to make 1-2 quarts of yogurt. You get to eat the rest!
So go forth and make yogurt!
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Have you ever made homemade yogurt? How did it turn out? Let me know by leaving a comment or emailing me at piquantprose [at] gmail [dot] com.
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