Homemade Yogurt: Why You Should Make It Too!

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.

Book Review: The Curious Cook by Harold McGee

Another book I found hiding in the university's chemistry library, this was a fairly fun and entertaining read. You may have heard of Harold McGee—he writes for the New York Times and has written a couple of other books (one of which I'm currently reading!).

The Curious Cook is basically a book about playing with food. By playing, I really mean performing pseudo-scientific experiments. The first part of the book reads like a series of lab reports, just lab reports from the best lab course you could ever take.

McGee talks about searing meat, sous vide cooking, beurre blanc and persimmons from an objective and scientific standpoint, creating experiments to explain the chemistry behind the concepts. While the chapters aren't as in depth as his tome On Food and Cooking, they're a lot more fun and accessible. Plus, I'm game to read any book that has a whole chapter on sorbet, particularly if that chapter has recipes and instructions for making your own.

Unfortunately, the book doesn't really go out with a bang. The second part of the book is about food and our health, including heart disease and cancer. Although his explanations of how food might affect our health did give me more information, they weren't as accessible as the first few chapters.

The highlights
- It's a fun, light, easy read.
- It piqued my scientific curiosity about food, and made me think about ways to ask and answer my own questions.
- The last few chapters were really a lot less fun to read.

The verdict:
This book would make the perfect present for a teenager who likes both science and food (but maybe doesn't have a huge background in either). It also has a few pretty handy reference tables scattered throughout the book. It's a cheap enough book that I would consider purchasing it as a reference book, especially if I made a lot of fruit ices/sorbets or cooked a lot of meat.

Emulsifiers 101

Have you ever tried to mix oil and vinegar? No matter how hard you shake or how vigorously you whisk, it doesn't really work. And if you put it on your salad, the oil will stick to the lettuce and the veggies, and you'll have a puddle of balsamic vinegar at the bottom of the bowl.

Here's what's happening:
For the purposes of emulsions, there are three kinds of molecules or substances.

- The first kind are the water-loving kind of molecules. In this category are things like vinegar and lemon juice—basically anything that water would mix into easily. For those of you that remember chemistry, these are generally polar molecules, attracted to the polarity of the water molecule. (Think of polarity kind of like a magnet--it can only stick to other things that can be magnetized.)

- The second kind are the fat-loving kind of molecules, like oil. These are things that don't mix with water. These are generally non-polar molecules, that don't have an interaction with the polar water molecule. The oils, however, generally do like to group with themselves (This is completely inaccurate, but think of these like a bunch of little velcro pieces. It'll help with the next part.)

- The third kind of molecule is one that has properties of both the water-loving and oil-loving molecules. In fact, it's got one end that's polar and one end that's non-polar. Think of it like a magnet with some velcro glued onto it. These are called emulsifiers.
[Cool side note: this is very similar to what soap is made out of--one end velcroes onto the grease on your hands or your pots, and the other end gets pulled away by the magnetic forces of the water.]


When you add an emulsifier to a mixture of oil and water, they magically combine with only mildly vigorous whisking. This is used in things like mayonnaise, in which oil and usually vinegar and/or lemon juice are combined. To make a stable emulsion (one that won't separate over time), you need all three things--water, oil, and emulsifier.

In common food applications, there are three prevalent food emulsifiers:
1. Egg yolk
2. Honey
3. Mustard
In processed foods, lecithin (often derived from soy) is added to many products (like chocolate) to help with emulsification.

Next time you make a salad dressing, try this instead, and you'll get a super creamy vinaigrette that doesn't separate on your lettuce.

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Creamy Balsamic Vinaigrette

Ingredients:
1T balsamic vinegar
salt
2T olive oil
1t Dijon mustard (the yellow stuff doesn't taste right, and it doesn't have enough emulsifiers in it)

Directions:
1. Dissolve the salt in the balsamic vinegar. (Salt will only dissolve in the water-loving liquids, so you should do this now, before you add the olive oil.)
2. Add the olive oil and the mustard. Whisk to combine. The vinegar and oil should combine together into a homogenous dressing.
3. If there's still uncombined oil and vinegar, add more mustard and whisk. If there's uncombined oil, add vinegar, whisk, and then add more mustard if necessary. If there uncombined vinegar, add oil, whisk, and then add more mustard if necessary.
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