Oil and water don’t mix.  That’s just the way it’s been through the millennia and the way things will always be.  In fact, “when oil and water mix” is now commonly being used by the hip kids to mean “when pigs fly”.**

But why don’t they mix?  What if you really, really, really, really mix them?  Let’s look at some fundamental properties of water and fats and see if we can’t get to the bottom of some of this.

Water:
Water is nothing but a compound made up of two hydrogen molecules and an oxygen.  Of all of the chemical compounds out there, it’s one of the simplest in composition.  However, our friend H2O has some amazing chemical properties.  It reacts with some metal oxides to form bases, and some non-metal oxides to form acids.  It becomes denser when heated from 0 – 4 Celsius, making liquid water more dense than ice.

Most importantly for us right now, though, is that water is highly polar, meaning that it has a positive charge at one end and a negative charge on the other.

Fats:
Fats are one of a larger class of organic compounds called lipids (which also include steroids, waxes & phospholipids).  Fats are big molecules that are made up of fatty acid (FA) molecules chemically bound to a glycerol molecule.

Fatty acids are generally long hydrocarbon chains with an even number of carbons with a carboxylic acid group on the end.  If there is one FA bound to a glycerol, that makes a monoglyceride.  Two FAs make a diglyceride, and three combine to form a triglyceride.  The carbon-hydrogen bonds in fats are non-polar.

Suspensions:
So the take-home message is that fats are nonpolar and water is polar.  The water molecules are all bonded together like magnets (positive ends bound to negative ends, so the fats can’t get in.  Water molecules don’t want to bond with something without a charge.  So, like a middle school dance, the water molecules are all grouped together, and so are the fats.  Nary the twain shall meet.

If you take oil and water and put them together, they form two separate layers.  If you give that a shake, some oil bubbles get down into the water, but shortly afterwards the oil is all back togehter.  It you shake it for a long time, you get tiny bubbles of oil in the water.  Congratulations!  You just made a suspension of oil in water!  If you let it sit, they’ll still separate back out, but the oil droplets will still stay suspended in water for a while.

Emulsions – Suspensions with an agent
There’s a special kind of suspension called an emulsion.  Emulsions are nothing more than stable suspensions.  They are stabilized by some third agent (emulsifying agent) that will form a thin film at the droplets’ surface, allowing them to mix.

A common emulsion that can be found in many refrigerators (in addition to hollandaise, beurre blanc, and ice cream) is mayonnaise.  I personally can’t stand the stuff, but we’re going to talk about it anyway.  In this case the water is being replaced by vinegar, which is basically an aqueous solution (so it’s water-based). The emulsifying agent is egg yolk.

You can make mayonnaise at home with oil, vinegar, & egg yolk. Basically, you add a little oil to the egg, mix, slowly add more oil to the mixture, then add some vinegar, then alternate between oil and vinegar until it’s all thoroughly emulsified.  Please don’t try to use that as a recipe for mayonnaise.

What happens is that the oil droplets become coated in the egg yolk, which keeps them from coming together to form a separate layer.  If you add the oil too fast, or if you add too much oil at a time, the droplets will come together before they can be forced into the egg yolks; the mayonnaise will curdle, or separate.   So the egg yolk allows the oil and vinegar to come together and stay that way.

So there’s your nutshell version of what happens with suspensions & emulsions.  We’ll revisit some of the chemical properties of fats and water in some postings coming up!

* With apologies to the Bee Gees.

** I made that up.

When Karyn introduced me a couple of weeks ago, Mary asked me about the difference between baking powder and baking soda.  I gave her a nutshell answer, but promised a full posting with some more info and clarification.

What I initially wrote was, “Baking soda is bicarbonate of soda. In the presence of an acid (vinegar, citrus, etc), it releases carbon dioxide gas causing bubbles. These bubbles leaven whatever it is that you’re baking. Baking powder is basically baking soda mixed with an acid in powdered form. When a liquid is added, you get the same reaction and the same leavening.”.

So let’s back things up a bit.  In my last post about beer, we talked about yeast metabolism.  When yeast are given a food source in the presence of oxygen, they produce energy and carbon dioxide gas (CO2).  That carbon dioxide gas being trapped within your dough is what causes bread to rise.

Of course, that process generally takes a couple of hours, so isn’t a good option for everything.  If you’re making batters or cookies, you might not want to wait that long and you might not want the yeastiness of baking bread in your chocolate cake.

Baking soda and baking powder are both chemical leaveners.  They undergo a chemical reaction in the presence of the right ingredients or conditions to produce the same CO2 gas.  And you don’t have to wait for hours…

Baking Soda:
Chemically, baking soda is NaHCO3.  In the presence of an acid, it reacts to produce our carbon dioxide gas and some kind of side product.  In the case of the classic science demo the ‘kitchen volcano’, vinegar (acetic acid) is mixed with baking soda, to produce CO2, liquid water, and sodium acetate* to produce lots of frothy, foamy ‘lava’.   It’s the carbon dioxide gas that causes the bubbles to form.

Common acidic ingredients that will produce this reaction are vinegars, buttermilk, yogurt, sour cream, fruit juices, honey, and molasses.

Baking Powder:
As I mentioned in my short answer, baking powder is a mixture of baking soda and an acid in solid form.  It also has a ‘filler’ component, often cornstarch. When you mix baking powder in the presence of a liquid (or heat, for slow-acting BP), the crystalline acid will dissolve and react with the baking soda, giving you the same reaction as above.  This is great for when you’re making a recipe without an acidic liquid ingredient.

The filler serves two purposes, it provides more volume to the powder so that it’s easier to measure (would you want to try to measure 1/16th tsp?), and keeps things dry inside the container.  Imagine what might happen if there was no filler and it was humid inside your pantry…

The dry acid ingredient can vary based on the kind of baking powder we’re talking about.  There are actually three types of BP: fast-acting, slow-acting, and double acting.
•    Fast-acting begins to react to form CO2 as soon as the liquid is added.
•    Slow-acting only starts to react in the presence of heat, so nothing happens until you pop whatever you’re making into the oven.
•    Double-acting has both types of acids, so you get a hit of reaction upon addition of your liquid ingredient and then another once the temperature starts to rise.  Most likely, the BP in your kitchen is double-acting.

Substitution:
If you’re out of baking powder, you can improvise using the following ratios to make the amount of BP the recipe calls for: 1 part baking soda, 1 part cornstarch, and 2 parts cream of tartar (the acid).  For example, if your recipe calls for 1 t. baking powder, you’d use 1/4t. baking soda, 1/4t. cornstarch, and 1/2t. cream of tartar.

If you’re out of baking soda, go to the store and buy some more baking soda.  Unfortunately, you can’t use BP to replace the soda because of the additional acid that it contains.  Too many acid byproducts can affect taste, texture, and color.

Extra credit:
I don’t know about you, but I couldn’t tell you when I bought the baking powder or soda in my pantry.  Because they rely on a chemical reaction to cause leavening, and chemicals can break down over time, you might want to test them out next time you reach for them (especially if company’s coming).  Here’s how:
•    Baking soda: ¼ t + 2t white vinegar should cause immediate foaming
•    Baking powder: 1t + ½ c hot water should do the same.
If they don’t, or if they’re sort of lethargic about it, you might want to think about replacing them.

Mary (and everyone else!), I hope this was more helpful in answering your question!

*Sodium acetate is edible in the quantities we’re talking about, and is even used as a flavoring agent.  It’s also what’s commonly used in heating pads to give off heat, but that’s another story altogether!

With Fathers’ Day just a couple of days away, I thought I’d do my inaugural cooking science post on something near and dear to many fathers’ hearts: beer.

Beer – it does a body good.  No, wrong liquid.

Beer – it’s what’s for dinner.  Well, maybe for some.

Beer – the other white meat.  See above.

Ok, enough goofing around – this is serious science here.

So what is beer?  We’ve all seen the commercials: pure mountain spring water, malted barley, American-grown Cascade hops… but what are those things, what do they contribute to the final product, and why does it make you feel the way it does?

Alcohol Production

Let’s start with yeast.  Yeast is the one thing they don’t mention in the commercials, but it’s what gives beer its intoxicating properties.  Yeast is a microorganism (a fungus, actually, but I don’t want to gross you out) that can thrive in environments with very little oxygen.  Most energy-producing metabolic processes (converting glucose into energy) in oxygen-rich surroundings produce only energy and two end products: carbon dioxide (CO2) and water (H2O).

Without the oxygen, though, the glucose is broken down into: energy + CO2 + alcohol (2CH3CH2OH).  This process of energy production in a cell in anaerobic conditions (w/o oxygen) is the very definition of fermentation.

Physiological Effects

We all know it’s the alcohol from the fermentation process that produces the physical/mental effects of beer, but why and how does it do that?

Essentially, alcohol molecules have a chemical nature that allows them to easily penetrate cell membranes.  The alcohol molecules have hydrocarbon groups similar to fats, and a very water-like -OH group on one end.  This makes it possible for alcohols to mix easily with both water (like the contents of your cells) and fats (like a cell membrane).

When alcohol enters your cells, it causes disruptions to the normal functioning of those cells.  Disruptions to the cells of our central nervous system bring on our feelings of intoxication.

Malting

Up there, I said that fermentation requires a source of glucose (a monosaccharide, or simple sugar).  In winemaking, that’s easy* – grapes are naturally full of glucose.

Beer, though, is brewed from grains that contain starches instead of glucose.  The good news (in this case) is that starches can be broken down into simple sugars through a process called malting.  In this two-step process, the grains (usually barley, but sometimes wheat, rice, millet, etc) are soaked in water until they sprout (usually a few days), and then heated and dried.

The sprouting grains produce enzymes (molecules that speed up reactions) that will break the starches down into their component sugars.  The heating stops the growth process so that you’re left with lots of simple sugars to feed the yeast.  The dried end product (barley malt) is often ground and can be stored for long periods of time.

Flavoring & Preservation

The beers of 1000+ years ago were basically just water, malted grain, and yeast, and they were consumed soon after brewing because they would spoil.  Flavoring agents that doubled as preservatives were first added to beers about that time.  Some of the first were rosemary & coriander, followed not too long afterwards by hops.

Hops are little cone-shaped flowers of the vine Humulus lupulus that have aromatic compounds in their sap and in little oil glands at the bases of their leaves.  The sap compounds (humulone & lupulone) provide a bitterness to the brew, and those from the glands (mostly terpene myrcene) provide aroma.  These same compounds also delay spoilage.

Production

Now that we’ve run through some of the theory, we’ll take a quick look at how that all comes together in the process of making beer:

Mashing: the dried barley malt is soaked in water, getting the starch-breaking enzymes fired up and doing their job.  The end result of the mashing process is a sweet brown syrup called wort.

Boiling: hops are added to the wort and they’re boiled. This pulls the flavoring compounds out of the hops, stops the enzymatic activity of the mashing, kills any bacteria, and concentrates the wort.

Fermentation: yeast goes into the cooled wort and fermentation begins.

Conditioning: getting rid of the spent yeast and other impurities.

Time for a cold one

Obviously, this is a very complicated subject that I’ve given only the most cursory overview of (and even that ended up being twice as long as I expected).  There are lots of other things we could have gone into, but I’m hopeful that this is enough background for now.

So the next time you pop open a can of Pabst Blue Ribbon, or a bottle of Racer 5 (my own fave at the moment), you can think about all of the history and chemistry and microbiology that went into that brew.  And don’t forget to regale your husband or dad (or wife or mom, for that matter) with the story of their favorite beer – I’m sure they’ll be highly impressed!

*I realize that there’s really nothing ‘easy’ about winemaking and it takes a huge degree of skill and artistry.  It’s just that the fermentation step is easier to get going.

Hello, Circle of Food!

I’m Kevin, and I’ve been blogging and tweeting as Tucson Food Dude for a little while now.  During the last couple of months I’ve really been enjoying writing about the Southern Arizona food scene and whatever else tickles my fancy.  Now I’m looking forward to blogging here about the science of cooking and all of the really cool things that go on in the kitchen, which I think of as the original science lab.  When nobody’s looking, I’m also going to sneak in the occasional non-science post, too.

Before I jump in straight into the science stuff, though, I wanted to take a minute to introduce myself.  I actually started cooking for my parents and sister when I was about 11.  That’s where my love of food and cooking got its start.  After five years in the Army, I spent some time in retail & restaurant management.  Along the way, I was trained as a baker (nothing formal or too fancy, strictly OJT).  This turned out to be sort of pivotal for me, because I started asking a lot of questions about things like: what causes bread to rise, what’s proofing all about, and why do granulated sugar and confectioner’s sugar have such different properties?  After asking these kinds of things for a while, I decided I finally had to go to college (I was a bit of a late bloomer, you see) to figure that stuff out and learn more about it.  A couple of years later, I was working in a biochemistry lab studying lipid metabolism.

So Karyn introduced me as ‘a biochemist by day’, which isn’t totally accurate.  I did research for about five years and then moved into informal science education, where I am today.

Whew.  I know it’s sort of a convoluted story (and you don’t know the half of it!), but I think it’s pertinent to what I’m writing and why I’m writing it.

Finally, I’ll leave you with a little bit about my home life.  I’ve got two amazingly bright and articulate daughters who are 14 & 12 (one of whom is a vegetarian), and I’m lucky enough to be with a wonderful, beautiful, talented woman who enjoys spending time in the kitchen as much as I do.  I’m sure they’ll all pop up in some of my posts every now and then.

And so I’ll end things here for the moment.  Thanks for taking the time to read through this, and I look forward to hearing some of your stories as well!

Kevin

PS:  If you have any burning kitchen sciency-type questions, send them my way.  I’m more than happy to take requests!