Does your cheese taste of microbes?

In our unit on microbes and exponential growth, we learned about the role of microbes in altering flavor and mouthfeel.  One of our favorite microbial foods is cheese:  Cheese would just be spoiled milk if it were not for microbes.

To kick off the class, we challenged the students with a taste test featuring four distinct cheeses:

A) Amish Blue Wheel
B) Emmental
C) Cheddar
D) Port du Salut

We also presented four different types of microbes, and a bit about natural habitats.    Can you guess which microbe belongs to which cheese? Answers below.

1) Propionibacterium (inhabit human skin)
2) Penicillium mold (grow in cool, moderate climate; some species have blue color)
3) Brevibacterium (grow especially well without much personal hygeine)
4) Lactococcus lactis (grow well in acidic conditions)




A. 2 – Blue cheeses are inoculated with a strain of Penicillium mold, Penicillium roqueforti. Needles or skewers are used during the inoculation, which is why blue cheeses often have distinct veins running through them.

B. 1 – Emmental is a type of Swiss cheese, which is known for its holes. These holes are bubbles excavated by carbon dioxide, a byproduct of lipid breakdown by Propionibacterium freudenreichii, subsp shermanii. Its close cousin, Propionibacterium acnes, is linked to acne.

C. 4 – Cheddar is an example of a wide variety of cheese types that rely on Lactococcus lactis for the first stage of ripening. L. lactis uses enzymes to produce energy from lactose, a sugar molecule common in dairy products. Lactic acid is the byproduct.

D. 3 – Port du Salut is a washed-rind cheese. The cheese surface is wiped or washed down with a brine that promotes the growth of certain bacteria in the air. A smear of bacteria can be directly applied to the surface to nudge along the process. Brevibacteria linens is commonly used during this inoculation. Ever get a whiff of stinky feet from your cheese? Brevibacteria linens is the culprit, in the cheese and on real smelly feet.

How Bubble Wrap Explains Crisp and Mealy Apples

In our unit of pressure, we learned about the difference between a mealy and crisp fruit or vegetable. It turns out that bubble wrap is a good analogy. 

From Smith et al (2003) Postharvest physiology and pathology of vegetables.

We already know that water inside the vacuole of a plant cell and the cell wall work together to keep the cell firm and rigid. When cells are full of water, a force, such as your bite, will puncture the cells and break open individual cells. That is when you experience the release of juices that accompany biting down on a crisp apple. On the other hand, sometimes the network of polysaccharides between cells becomes weak, and when force is applied, the cells separate from each rather than are cleanly punctured through. This is when we encounter the classic mealy apple. With time, the polysaccharide “glue” that binds cells to each other begin to degrade. The cells also begin to lose water. This is why apples that have been stored incorrectly for long periods of time often turn mealy.

Take bubble wrap as an analogy. When the bubbles in bubble wrap are sealed and full of air, it is very easy to get that satisfying “Pop!” when you puncture the bubble. However, when the bubbles are not fully inflated or have already been punctured, then it is much harder to pierce another hole in the same bubble.

Josiah Citrin on Viscosity in French Sauces

Josiah Citrin visited class to discuss viscosity’s role in sauces and its effect on flavor and mouthfeel. Josiah is the chef/owner of Mélisse in Santa Monica and co-owner of Lemon Moon in West LA. 

Using the sauces that he brought for us to taste, Josiah traced out the evolution of sauce making from pre-1970s to present day. Traditional French sauces are sually thickened with a mixture of cooked butter and flour (roux). Consequently, they were thick and heavy on the palate. Then, in the 1970s, a shift towards more delicate preparations and sophisticated presentation took place. This nouvelle cuisine caused cooks to prepare sauces with less flour, relying more upon high quality butter, vinegar, and other less viscous liquids. In the 1990s and 2000s, the introduction into restaurant kitchens of techniques and ingredients previously only found in industrial food preparation saw the use of Ultratex 3, tapioca starch, xanthan gum, and other additives in sauce making.

A taste test of red wine sauce made 3 ways made this evolution particularly clear to us:
i. thickened with flour
ii. thickened with puréed shallots and butter
iii. thickened with Ultratex 3 (a tapioca-derived starch)
While the viscosities of the sauces were similar, the taste differences were quite striking. Each additive has its particular taste, and heat also creates new flavor molecules out of the base recipe.

A few of Josiah’s tips for sauce-making:
1) When making hollandaise, add salt at the beginning of preparation, before adding butter.
Why? Salt (NaCl) and water are both polar molecules, which means one part of the molecule is negatively charged while the other part is positively charged. Generally, like dissolves like, and water does dissolve salt very well. However, fat is nonpolar, and salt does not dissolve well in it. Thus, to make evenly salted hollandaise, make sure to salt while the sauce is still mostly water.

2) To make a very light and airy sauce, such as the mint cilantro cashew sauce, set with gelatin and foam with an iSi siphon.
Why? The iSi siphon produces a temporary foam consisting of air bubbles entrapped in a network of sauce molecules. However, the bubbles are unstable and will merge, causing the foam to quickly deflate. Introducing gelatin to the sauce, however, strengthens the network and extends the lifetime of the foam.

3) Need to keep sauces warm? Store them in thermoses instead of in open containers in water baths.
Why? Sauces stored in open containers will evaporate, and the flavor and mouthfeel will change due to the reduction of volume. Capped thermoses are perfect at trapping heat and also preventing evaporation.

Plants under pressure

In our unit on pressure, we used plants as a model system. What makes lettuce crispy? How do you revive wilted lettuce? It’s really all about pressure- turgor pressure, to be exact.


We prepared tasting samples of dehydrated grapes (aka raisins) and kale chips to demonstrate the vital role that water and pressure play in plants. Under normal conditions, grapes are juicy and firm, and kale is hardy and stiff. We placed both in a dehydrator, which works as a low-temperature oven (~130 °F/54 °C). Water evaporates, and the cells lose turgor pressure and shrink. The grape becomes soft and mushy on the inside, and the kale, which is normally so tough and sturdy, shatters like a chip.

And for reviving that wilted lettuce? Soak it in cold water, of course.


Dehydrated Grapes

Boiling water

1) Wash grapes well.
2) Bring a pot of water to a boil. Blanch* grapes in boiling water for 30-60 s.
3) Pat grapes dry.
4) Places grapes on dehydrator racks. Turn on dehydrator. If it has a temperature setting, some recipes suggest 140 °F. Our dehydrator has only one temperature setting of ~130 °F, so we just went by touch. A wrinkled grape with a still-moist center takes 3-4 hours.

*Blanching dissolves the waxy cuticle on the surface of grapes. The wax is a natural defense mechanism against water evaporation.

Kale Chips

Olive oil
Paprika, cumin, other seasonings

1) Rinse and dry kale leaves. Cut lengthwise in half, and again in thirds.
2) Toss kale with olive oil in bowl. Sprinkle with salt, pepper, and other seasons.
3) Arrange leaves in single layer on dehydrator racks. Turn dehydrator on. Let run for ~2 hours.

René Redzepi and Lars Williams on Deliciousness

René Redzepi and Lars Williams of Noma and Nordic Food Lab finally made it to UCLA!

We had quite an adventure leading up to their lecture, which involved mole crabs, sand fleas, live crickets, lost luggage, liquid-nitrogen-seaweed ice cream, and much more.

René Redzepi spoke about the pursuit of ‘deliciousness’:

“It’s not about creating dishes, but understanding deliciousness…to provide knowledge and scientific concepts for chefs.”

René’s ideology was born when he had a eureka-moment while grating and preparing horseradish.

“Some days the horseradish was sweet, some days it was acidic, some days, spicy to the point where I had to walk away. Sometimes the shape was short, sometimes long. How is it that we’d be able to create a consistent menu, with such variable changes week by week, season by season?”

He voiced what he thought was the answer.

“A chef’s intuition, combined with scientific know-how.”

Hence, the birth of the Nordic Food Lab. This is Redzepi and his team’s solution to creating a medium between food and science. Here, his talented team delves into the concept of deliciousness: how can they create and optimize using the ingredients that natures provides? (Remarkably, a good deal of their experimentation happens inside a houseboat shored in the picturesque Copenhagen harbor).

Head of Research & Development at Nordic Food Lab, Lars Williams, introduced a sampling of their recent experiments including how to modify and generate unique flavors using local and natural ingredients. One of the team’s favorite recent topics is fermentation, and a delicious example they shared was barley koji. The procedure is as follows.

  1. Crickets are blended up and mixed with barley
  2. The mixture is left to incubate, during which time, enzymes (such as amylases and proteases) in the barley and cricket guts, as well as microbes, take action.
  3. The resulting moldy mass is transformed into a nutty sweet delectable treat. (They did state they wanted to increase the amount of critters on the menu).

Nordic Food Lab also experiments with native Danish ingredients, such as seaweeds: a delicious example was their seaweed ice cream, which was created by extracting flavors of dulse into ice cream. To determine the optimal conditions for flavor extraction, they did a series of experiments to quantify levels of glutamate, aspartate and alaninate. You may be familiar with glutamic acid as a flavor enhancer, monosodium glutamate or MSG, more commonly known as small, powdery white crystals at the Asian market, or heavily-dosed out in Chinese food.

These are just a couple of examples of cutting-edge work emerging from the Nordic Food Lab; the possibilities are endless, and it will be exciting to follow their progress as they explore and share these exciting new innovations. Check out their recent publication to learn more about Seaweeds for Umami Flavor in New Nordic Cuisine.

For those you who didn’t get to taste the cricket sauce (or just can’t get enough), hit up LA Weekly’s Squid Ink for an additional recap of last night’s lecture.

Gary Menes’ Veggie Platter

This week’s lecturer is Gary Menes. He is the chef at Le Comptoir, a pop-up restaurant at Tiara Café in LA. 

Gary Menes and sous-chef Wesley Avila weighed in on our topic of the week, “Pressure,” with their version of the veggie platter.  There were 20-odd vegetables and fruits present, including pickled onions, the season’s first cherries, pickled orange segments, Okinawan sweet potato, and quickly sautéed fava beans.

Gary packed cherries in a bag and used a cryovac machine to suck out all the air in the bag. The resultant vacuum compresses and bruises the cherries, changing their texture and flavor in the process.

Want to make quick-pickled onion petals? Slice the onion in quarters or halves and peel apart the layers to get petals. Heat up a quick-pickling solution of 3 parts water : 2 parts red wine vinegar : 1 part sugar. Once hot, submerge the petals and let rest for 30 minutes.

“It’s all about sugar” – Barbara Spencer

Barbara Spencer of Windrose Farm in Paso Robles was our lecturer on the topic of phase transitions. 

“Why are carrots harvested after winter particularly sweet?”

Plants use sugar as an internal antifreeze. This is an example of the concept of freezing point depression. When a solution freezes, the molecules into a crystalline structure. However, when impurities are introduced to the solution, they block the molecules from clustering together and freezing. In the case of carrots, sugar is the impurity, and it keeps the liquid inside the plants from freezing at 0 °C. This defense mechanism against frost translates into carrots that taste extra sweet to us. Even on a daily basis, Barbara always picks her carrots and melons before the sun comes up, because sugar levels increase at night. Strawberries ripen at night, too.

Image courtesy of

Out where the farm is in Paso Robles, the valley makes for a very active microclimate. The difference between daily temperature highs and lows can be as large as 50 °F. Apples, which need a certain number of hours of frost, thrive well there.

Storage is just as important as growth, and Barbara invested in a refrigerated truck for transporting vegetables. Leafy greens always need water, and this is why supermarkets and farmers are always spraying or misting. There is a rule of thumb that every hour lost in not cooling freshly picked vegetables to the proper temperature equals one less day of shelf life.

We were surprised to learn about the storage capabilities of some apple varieties, such that you can keep them for months on end. They’ll be good right after picking, become very gnarly quickly, and then, if you wait long enough, they’ll taste fantastic again. Which varieties do you know are like that?