Cooking for Geeks: Real Science, Great Hacks, and Good Food (60 page)

Note that straight-up lime juice won’t work, because the alginate will precipitate out in the presence of strong acids. If you’re willing to experiment further, try using sodium citrate to adjust the pH.

PHOTO USED BY PERMISSION OF ANN BARRETT

Ann Barrett is a food engineer specializing in food textures. She works for the Combat Feeding Directorate of the U.S. Army Natick Soldier Research, Development and Engineering Center (NSRDEC).

What does a food engineer do?

It’s like applied chemical engineering but for food. The training focuses on how to process food and how to preserve food, looking at food as material. I happen to have a specialty in food texture or food rheology; rheology means how something flows or deforms. My PhD topic was on the fracturability of crunchy food. How do you measure crunchiness or fracturability, and how do you quantitatively describe the way a food fails? When you chew a food and it breaks apart, can you describe that quantitatively and then relate that to the physical structure of the food?

Tell me a little bit about the NSRDEC.

There are several RDECs (research, development, and engineering centers) throughout the country. NSRDEC is focused on everything the soldier needs for survival or sustenance, aside from weaponry: food, clothing, shelters, and parachutes. The food part is largely driven by the fact that the military is potentially deployed in every kind of physical environment, so we need a wide range of foods to support soldiers operating in a wide range of situations. They have large depots of rations, and that drives a very long shelf-life requirement. Most of the food that we make needs to be shelf-stable for three years at 80°F / 26.7°C. That is not to say that the soldier will always eat something that’s three years old, but they definitely might. That drives a lot of the research here; foods that are shelf-stable but also good, that the soldiers will want to eat.

It must be really interesting to work with the constraints that you’ve got while trying to preserve flavor and texture. How do you go about doing that?

Well, it’s often one part experience or knowledge combined with two parts trial and error. There’s a lot of bench-top development here. Most of my experience has been in processing and engineering analysis of food, but I do have a project now where we’re trying to develop flavors for sandwich fillings. All flavors are chemicals, so you can replicate a natural flavor by knowing what the chemistry is.

For example, we’re working on a peanut butter filling for sandwiches. We’re trying to make a chocolate peanut butter flavor, a bit like Nutella. We have the peanut butter formula, and we’ve been looking at adding cocoa and at different chocolate flavors. We put three into storage to see how they would work, and two of them came out just okay, and one of them was delicious. When you’re developing something, you have to look at a number of different ingredients to see what works. There will be changes in both the flavor and texture of a food during long-term storage. Flavors tend to become less intense, or off-flavors might develop. Texture can degrade by moisture equilibrating, say in a sandwich, or by staling. There are a multitude of flavors that are commercially available, and also a multitude of ingredients that will adjust texture — for example, starches and gums for liquid or semi-solid foods, enzymes and dough conditioners for breads. So during development you need to optimize a formula to make sure the food is good after you make it and also good after storage.

Even with all the hard science, you still have some degree of, well, “Let’s just try it and see what happens?”

Oh, absolutely. You make a product up for a project, sample it, store it, and then sample it again. Everything is actually tasted here, and as a matter of fact, part of our duties is to go over and participate in the sensory panels because the food scientists here, the nutritionists, the dieticians, are all considered expert tasters. The first thing we do is make our product on the bench and then put it into a box that’s 120°F / 49°C for four weeks. Those conditions approximate a longer period of time at a lower temperature; it’s just a quick test to see if quality holds up. If the product holds up, next is 100°F / 38°C for six months; that’s supposed to approximate the quality you would get at three years at 80°F / 26.7°C. Then you have to check
that it’s microbiologically stable, so it goes to the microbiologist for clearance, and then you can ask people to come and evaluate it. We rate the appearance, aroma, flavor, texture, and the overall quality.

How does the science of food texture work into enjoyment of food?

There are expected textural properties of whatever food category you’re dealing with. Sauces are supposed to be creamy; meats are supposed to be at least somewhat fibrous; bread and cake are supposed to be soft and spongy; cereals and crackers are supposed to be crunchy. When texture deviates from what’s expected, the food quality is poor. If you are going to measure and to optimize the texture of a product, you need to pinpoint the exact sensory properties you want.

For example, for liquids, flowability or viscosity is the defining physical and measurable characteristic. There are “thin” liquids and “thick” liquids, and you can often change thin to thick by adding hydrocolloids or thermal treatment. Solid foods come in many different textural types. There are elastic solids that spring back after deformation (Jell-O); there are plastic solids that don’t (peanut butter). Then besides “solid” solids there are also porous solids — think bread, cake, puffed cereal, extruded snacks such as cheese puffs. Porous foods have the structure of sponges, and like a wet versus a dry sponge, they can be elastic or brittle.

Somebody cooking in the kitchen is actually manipulating these things both physically and chemically?

Yes, that’s exactly what cooking is. Take cooking an egg. The protein albumin will denature with heat, causing molecular crosslinking and solidification. Another example is kneading bread dough, which is a mechanical rather than a thermal process that makes the gluten molecules link up; that gluten network is what allows the bread to rise because a structure is developed that will hold gas liberated by yeast. And of course, every time you use cornstarch or flour to thicken a gravy or sauce, you’re employing a physico-chemical process. Heat and moisture will make the starch granules absorb water and swell and then bleed out individual starch polymers, which are like threads attached to the granules. The starch polymers then entangle, creating an interconnected structure that builds viscosity. That’s why your gravy gets thick.

Flour (roux method)

Create a simple roux by melting 2 tablespoons (25g) of butter in a saucepan and then adding 2 tablespoons (17g) of flour. Stir while cooking over low heat until the roux sets and begins to turn light brown, about two to three minutes.

Add 1 to 1½ cups broth or stock; whisk to combine. Simmer over low heat for several minutes, until the gravy has reached your desired thickness. If the gravy remains too thin, add more flour. (To prevent clumping, create a slurry by mixing flour with cold water, and add that.) If the gravy becomes too thick, add more liquid.

Cornstarch

Create a cornstarch paste by mixing 2 tablespoons (16g) cornstarch with ¼ cup (60g) cold water.

In a saucepan, heat up 1 to 1 ½ cups broth or stock. Add the cornstarch and simmer for 8 to 10 minutes to cook the cornstarch. If the gravy remains too thin, add more cornstarch paste. If the gravy becomes too thick, add more liquid.

Notes