Week 10: Fermentation, Harvard Style

Fermentation, such as with yeast in this pepper wreath, helps round out Week 10

And then we came to the end. In the final week of the Harvard online food science class, the subject header was "fermentation," but the introduction of a little something called "transglutaminase" was a magic carpet ride that transported us to the world of crazy enzymes.

Two famous creative guys fired up the week's lecture series: Wylie Dufresne of wd~50 and David Chang of Momofuku. Chef Wylie and colleague Ted Russin from the Culinary Institute of America talked about the enzyme transglutaminase, or "meat glue," that just may be the biggest "oh, wow" concept of the whole course. These guys are making what you've never thought of before - noodles entirely of shrimp, and pasta made of carrots. They also show how they "glue" cuts of steak and fish together, a powerful concept. It means there's no trim loss. You can stick meat together when you apply an enzyme paste, roll it up like cookie dough, and slice it in perfect rounds. That's good for the guest and good for the restaurant. You just knew science was cool. Week 10 felt like the adage of old, save the best for last.

Over at Momofuku, David Chang and staff showed how to create fermentation reactions that lead to new foods like their hozon (Korean for "preserve") and a new spin on kimchi. They also made a critical point - do not try this at home. They've spent countless hours working in specific conditions to ensure food safety while tweaking around with enzymes. Research if you must, but always mind the safety.

There's also an excellent section on how enzymes cause browning in food. You know this if you've cut up an apple. Many fruits have an enzyme called polyphenol oxidase. This enzyme reacts with phenolic compounds in the presence of oxygen to make that brown discoloration when you cut. That's because the fruit normally keeps polyphenol oxidase and phenolic compounds separate in cell walls, but once you break those walls by cutting or bruising, they come together, hit the oxygen and turn everything brown. How can you decrease this rate of browning? Denature that enzyme! Do it by adding acid such as lemon juice, or with very high temperature (cooking it). Or you can make the enzyme less active by using low temperature, limiting exposure to oxygen or using high salt concentration. In pastry school when making tart tatin, we'd slice up the apples but then drop them into an acidified solution of lemon juice and water. That kept them out of the oxygen and into an acidic state.

There's another reaction that happens because of cell damage - pungent, flavorful fumes, like when you slice up garlic and onions. That enzyme is alliinase. Now sometimes you get a recipe that has you finely chop or mince garlic and onions to increase the cell damage, so you gain more flavor. Or you get a recipe that calls for garlic and onions to be roasted or sauteed at high temperature to decrease their pungency by inactivating the enzyme.  

Tip No. 1: A sliced garlic clove will have less flavor in the dish than a minced one - and now you know why!

Tip No. 2: ATK says the only way to truly protect your eyes from tearing up when chopping onions is with goggles. 

The week also covers microbes, which impact baking and fermentation for things like cheese, wine and vinegar. You also get an equation that allows you to figure out just how many microbes are present in a food, based on how they grow exponentially.

Equation of the Week: N(t) = Noe to the kt power, where No is the initial number of microbes and k is the rate of growth.

A-Ha Moment of the Week: America's Test Kitchen explains why pesto darkens (remember browning caused by enzymes?) Adding parsley to the pesto will help keep the pesto bright green. Parsley contains vitamin C, and since vitamin C is acidic, you see why parsley can help denature the enzymes.  

Science is golden!

Next: My Final Project (and it involves Velveeta)