I have recently come to know Miss Silvia. She’s from Italy, weighs a good 14 kg and even my wife welcomed her in our kitchen! As home brew espresso afficionados will know by know, I’ve become the proud owner of an espresso machine from Rancilio! She’s been around for a number of years, and is one of the most popular among prosumer espresso machines available before you take the step up to double boiler machines that allow simultaneous brewing and steaming. Every place that is (proud of) serving espresso uses these machines, but their price is well beyond most coffee lovers budget. The good news however is that even single boiler machines can produce excellent espresso!

The first time I offered the science of espresso any thought was when reading Jeffry Steingarten’s accounts of his espresso adventure (in “It must’ve been something I ate”) which brought him all the way to Italy and Illy and then back again to Manhatten where he set up 14 home espresso machines in his kitchen. This is also where I first was made aware of the fact that 7 g of coffee should be used for a single espresso (which is considerably more than the 5-6 grams found in the Nespresso capsules).

Since I decided to buy an espresso machine I have been devouring sites written by and for coffee enthusiasts: CoffeeGeek, Home Barista and Espresso! My Espresso! to mention a few. You’ll be surprised how much one can possibly write about espresso!
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Extraction of peppermint leaves with hot water

Water is a polar molecule, meaning that one end has a small negative charge and the other a small positive charge. Because of this water is a very good solvent for other polar molecules and ions. For instance water is the solvent of choice for substances that provide taste, be it salt, sour, sweet or bitter as these are normally quite polar molecules.

A general rule is that the solubility of molecules and ions increases with the temperature of the water. Extractions are therefore faster if the water is boiling. This is the reason why we use hot water to extract tea leaves or ground coffee beans, even if we want to prepare ice tea or ice coffee. But by lowering the temperature and extending the extraction time we can change the relative proportion of what we extract. It therefore makes perfectly sense that different temperatures are recommended for different types of tea. Using different temperatures for the same kind of tea will of course also influence the flavor profile.

Polar molecules are more easily extracted than non-polar molecules. This is evident if we leave a tea bag for a long time in hot water. The bitter taste is due to the slow extraction of large polyphenol molecules which are less soluble in water. If tea is brewed at a lower temperature, less of the bitter tasting substances will be extracted.

Although water is polar, less polar and even non-polar substances can be extracted with water, especially if the water is boiling hot. You do this every day when prepare coffee. If you take a close look at cup of freshly brewed coffee you can notice small pools of oily substances floating on top of the coffee. The more severe conditions used when extracting coffee to make an espresso ensure that even more oily substances are extracted. Other examples of extraction using water in the kitchen include preparation of stock, soups and gravies.

The principle of extraction is simple, but a number of questions remain largely unexplored with regard to flavor: How do ions affect extraction? What role does pH play? How does temperature influence flavor? There is surprisingly little research on this that includes a sensory evalution.

It’s time to sum up the contributions to the food blogging event They go really well together (TGRWT). There were five seven contributions plus a number of suggestions in the comments to the announcement post and I would like to thank you all very much indeed for taking time to experiment in your kitchens! Here are the results (in no particular order):

Lamiacucina: Candied, chocolate coated Garlic. Garlic cloves were heated in a strong sugar-coffee solution. Cloves were then dried and coated with chocolate. Succession of taste and aroma: strong, unpleasant character of garlic. Bloggers verdict: disappointing!

Blog & White: Chocolate-Coffee Mayonnaise with Garlic. Adapted from Hervé This’ chocolate mayonnaise with added coffee and garlic. Succession of taste and aroma: chocolate aroma is followed by taste of garlic and sweetness of chocolate, coffee aftertaste. Bloggers verdict: Interesting (but wife hates it!).

Should you eat that: Mocha Tofu Mousse with Garlic. Roasted garlic cloves were added to an adapted version of Scharfenberger’s mocha tofu mousse. Succession of taste and aroma: coffee followed by chocolate, then a subtle, sweet, roasted garlic aftertaste. Bloggers verdict: I would definately make it again!

M’s blog: Mocca garlic creme brulee. As the name suggests a creme brulee with espresso, chocolate and a garlic clove. Bloggers verdict: Tasted like mocca creme brulee.

Khymos: Coffee espuma with garlic and chocolate. Coffee and cream espuma with added chocolate and roasted garlic. Succession of taste and aroma: coffee with sweet taste, then a faint chocolate aroma followed by a garlicky aftertaste. My verdict: Aromas blend well together. Would use less garlic for dessert version.

Entries added after first posting:

GrapeThinking: Roasted garlic dipped in melted chocolate with coffee beans. Succession of taste and aroma: Roast garlic doesn’t have much of a smell. Chocolate and coffee always smell good. Bloggers verdict: Good aroma. Taste was good in the beginning; slightly funky aftertaste. Texture of garlic was good.

Kompottsurfer: Espresso-risotto with bitter chocolate, tomatoe and mozzarella (posting in German). Bloggers verdict: Color was a disaster, and difficult to get relative proportions right. But aroma worked out prette nice.

From the different comments it seems that garlic is a difficult beast to tame, especially when used raw. A major challenge is finding the right balance between the aromas. Garlic was either too strong or almost absent. Chocolate and coffee however seem to go very well together (and my preliminary search for odor activity values confirm this – more on this soon!).

I also find it interesting that ratios of chocolate, coffee and garlic used influence the succession of aroma and taste (“>” meaning “followed by”):

Is it a coincidence that coffee is the first aroma noticed in the two “foamy” preparations or is this simply a result of the different ratios used?

I should mention that I also tried to make a chicken mole using the three ingredients. Based on a couple of recipes from the net and some tinkering I ended up with a chicken mole that had a little too much chocolate… It tasted … eh … strange, so I decided to add balsamic vinegar which helped a lot! The coffee blended in very well however, so this is how I would make it the next time using less chocolate:

Chocolate coffee chicken mole
800 g canned, crushed tomatoes
750 g chicken breast,
1 red chili, chopped
2 t chili paste
2 onions, chopped
6 cloves of garlic, chopped
3 dL coffee
150 g pistacchio nuts, chopped
1 t ground cumin
30-50 g dark chocolate
2 T sugar
1-2 T balsamico vinegar

Brown onions. Add the rest and simmer. Season to taste with chocolate, balsamico vinegar and sugar. Serve with rice. Sprinkle with coriander/cilantro or ruccola/rocket salad.

There were also a number of recipe suggestions in the comments to the three posts on the coffee/chocolate/garlic theme.

(Photo by vintage_patrisha at flickr.com)

4. Learn how to control the texture of food

Taste and flavour normally get more attention when food is discussed, but the texture of food is equally important and our tongue is very sensitive, not only to taste and temperature, but also to the texture of food. The texture of food determines it’s mouthfeel and it is related to many physical properties of the food. Wikipedia lists the following aspects of mouthfeel (click to see the full description of each aspect) which can be useful when analyzing food:

Adhesiveness, Bounce/Springiness, Chewiness, Coarseness, Cohesiveness, Denseness, Dryness, Fracturability, Graininess, Gumminess, Hardness, Heaviness, Moisture absorption, Moisture release, Mouthcoating, Roughness, Slipperiness, Smoothness, Uniformity, Uniformity of chew, Uniformity of bite, Viscosity, Wetness

I will barely scratch the surface of how texture can be controlled by highlighting a couple of topics and point you to further resources. Hopefully it will spark your interest and give some new ideas for you to play with in the kitchen. Those interested in a comprehensive review of food texture are referred to the CRC handbooks on food texture (volume 1: semi-solid foods, volume 2: solid foods).

What determines the texture of food?
Put very simple, it’s the relative amounts of air, liquid and solids that determines the texture of food. This is complicated by the fact that liquids have different viscosities. Furthermore the air, liquid and solid ratio is not necessarily constant. A liquid can solidify or evaporate, solids can melt or dissolve, and air bubbles can escape during cooking or storage. An elegant but quite abstract way of describing the complicated mixtures of air, liquids and solids found in food, is to use the CDS formalism (CDS = complex disperse systems), introduced by Hervé This.

(Photo by Subspace at flickr.com)

How can texture be controlled and changed?
Texture can be controlled by temperature, pH, air/liquid/solid ratio, osmosis, hydrocolloids and emulsifiers – to mention a few. Here’s some examples:

(Photo by Trinity at flickr.com)

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Check out my previous blogpost for an overview of the tips for practical molecular gastronomy. The collection of books (favorite, molecular gastronomy, aroma/taste, reference/technique, food chemistry) and links (webresources, people/chefs/blogs, institutions, articles, audio/video) at khymos.org might also be of interest.

Ferran Adria’s espresso foam, named “Espesso”, is indeed a fascinating concoction, created in cooperation with coffee producer Lavazza. The word espesso is a combination of espresso and the Italian word spesso, meaning thick. Just luck at the thick lucious foam.

The invention has been commented on thoroughly in the blogosphere. See for instance Skillet Doux and Movable Feast – both feature some nice close-up pictures of espesso (including the one above).

Espesso has been available in Europe since 2002 (anyone know where?), but was just recently introduced in the US. Appearantly, the foam is served warm in Europe, but has been served cold in Chicago, at Lavazza’s three locations there.

According to the reports, espesso is made from espresso and a “secret” ingredient. The ingredients are mixed and left to settle for 12 hours under pressure. The product is then dispensed from the iSi Gourmet Whip (more info here, the propellant gas is nitrous oxide, N₂O). As a chemist I certainly wonder what the “secret” ingredient is? If it is true that espesso has been served both warm and cold, they would need to use a thickening agent which is not very sensitive to temperature. Also, it appears that the foam once served is not stable for more than a couple of minutes.

My best guess would be xanthan and guar gum, or possibly a combination of the two. These hydrocolloids show thixotropic properties – when subjected to pressure/agitaion they soften, but then they jellify again afterwards. In other words – they could be easily dispensed through a siphon and would then solidify in the cup. Also, xanthan and guar gum are relatively temperature independent with regard to their thickening properties. Check out the INICON manuals on texture for great (and FREE!) information on these and several other hydrocolloids.

Update: The Lavazza homepage now features a video and a tool to find your nearest Espesso!