I recently stumbled over “Norwegian egg coffee”. At first I thought it was a joke, but it turned out that this is indeed an “egg coffee” – coffee prepared with an egg! I have never heard about it here in Norway, but the fact that it’s popular among Americans of Scandinavian origin in the Midwest suggests that it could be something immigrants brought with them from Norway (feel free to fill me out on the historic origins of this!). I mentioned egg coffee to my mom, and although she had never heard of it before, she did mention that skin or swim bladders from fish were used when boiling coffee to help clearify it. In fact the Norwegian name for this – klareskinn – literally means “clearing skin”. The English name is isinglass (thank’s Rob!). Could it be that the fish skin originally used was replaced by eggs, perhaps due to a limited availability of fish in the Midwest? After all, both are good protein sources.


Egg coffee is amber colored and you can clearly see some precipitate from the egg-coffe mixture. If serving the coffee warm it seems to be difficult to totally avoid the precipitate unless you filter the finished coffee through a cheese cloth or filter paper. The coffee in this picture has not been filtered yet.

When looking into the chemistry behind this it isn’t as strange as it may sound. Fish skin as well as eggs contain proteins. The addition of proteins while preparing the coffee serves two purposes: 1) it helps the coffee grounds to flocculate, allowing them to sink faster to the bottom of the pot (this effect is probably more pronounced when using eggs) and 2) the proteins bind irreversibly to astringent and bitter tasting polyphenols in coffee to form insoluble complexes that will precipitate. The end result is a clearer coffee with a pleasant and mild taste. The bitterness is only barely noticeable, but the coffee still has enough “body” so it doesn’t feel too thin!

Norwegian egg coffee
80 g coarsly ground coffee (rouhgly 200 mL)
1 egg
100 mL cold water
2.5 L boiling water
250 mL cold water

Mix coffee with an egg and 100 mL cold water to a thick paste. Add this mixture to the boiling water, stir carefully and leave to boil for 2-3 min. Remove pot from stove and add the remaining cold water. Let the grounds settle for a couple of minutes, skim off any floating particles, filter through a fine meshed sieve, a cheese cloth or filter paper and serve.

The first time I made this I stirred quite a bit to break up the big lumps. But I was curious whether stirring had any influence on the amount of fine particles, so I repeated the whole process with as little stirring as possible. The lumps of ground coffee where significantly larger, but I couldn’t really see a difference on the prepared coffee. There was however a small difference when looking at the glasses from below (see picture below). My conclusion so far is that there is not a big difference, and that it’s OK to stir a little at the start to break up the biggest lumps. This will also allow a more complete extraction of the ground coffee.

Difference between much (left) and little (right) stirring as the coffee boils as seen from the precipitate at the bottom of a glass of egg coffee.

The addition of the cold water helps formation and settling of the precipitate. Home brewers talk about a “cold break” when they cool wort rapidly in order to precipitate proteins which have been extracted from the malt. And while we’re talking about beer chill haze also comes to my mind. This is the cloudiness that occurs upon cooling beer, and again it’s caused by precipitation of protein-polyphenol complexes. The effect of adding only 10% cold water to the still hot egg coffee is of course limited, and won’t really be enough to give a “cold break”. But since egg coffee has a pleasant taste even when cold, I have decided to cool a whole pot of egg coffee before filtering it. I may post more on how this turns out later, but initial tasting suggests that it’s going to be a very nice iced coffee!

The interesting thing about the protein-polyphenol complexes is that we also encounter them when drinking wine (a quick reminder here that polyphenols is a group of compounds which includes tannins). There’s a nice experiment you can do to illustrate this which has been published on Khymos previously. When we drink red wine, the tannins react with proteins in our saliva to form water insoluble protein-tannin complexes. A precipitate is formed and as a result, the lubricating properties of the saliva are lost and our tongue feels rough and dry. In other words, we experience the astringency of the red wine. To ilustrate this, try the following (I was first introduced to this experiment at the 2004 International workshop of molecular gastronomy in Erice):

Take a sip of a dry red wine, preferably rich in tannin. Keep the wine in your mouth for 10-20 seconds without swallowing. Spit it into an empty glass and watch how a precipitate forms (this might take a minute or two). Notice how the color changes from red to light red or even pink (see picture below). Rinse your mouth by chewing a piece of bread and drink some water. Take a small sip of the wine that you just spat out (if you dare!). Since the tannins of this wine have already reacted with your saliva, it is as if they were removed from the wine, leaving a fad and flat wine without much taste at all.

Top: red wine. Bottom: formation of precipitate in red wine mixed with saliva.

The saliva flow rate and the concentration of proteins varies from person to person (the latter with a factor of 20). Furthermore the flow rate and protein concentration also varies throughout the day and is also influenced by what you are eating/drinking and even by the smell of food. As a consequence, a person with a high saliva flow rate and/or a high concentration of proteins is more likely to approve of a red wine rich in tannins than someone with a low saliva flow and a lower protein concentration. Knowing this, you should not be surprised that wine preferences can be very individual.

The products of the Maillard reaction provide tastes, smells and colors that are much desired and lend their charachteristics to a variety of foods. In this post I will focus on the factors that influence how fast the Maillard reaction proceeds. And more specifically I’ll give examples on how the Maillard reaction can be speeded up. This is not about fast food, nor is it about saving time. It’s more about controlling the browning reaction by speeding it up or slowing it down in order to get a desired end result.

The Maillard reaction is, to put it simple, a reaction between an amino acid and a sugar (there’s more on the chemistry at the end of the post). To speed it up you can do one or more of the following:

Chances are you have already utilized this in the kitchen without knowing. When eggs or milk are used for glazing, they act as a protein source for the Maillard reaction, giving a nice brown color. Milk also provides lactose which is a reducing sugar. You’ve probably also observed that temperature does influence browning. Water content is indirectly related to temperature – as long as there is water present, temperature will stay below 100 °C. But once the bread crust dries out the conditions are just right to get the Maillard reaction running.

The same principles are applied to microwaveable pies. The microwaves primarily interact with water and hence only bring the temperature up to the boiling point of water. In order to get sufficient Maillard productcs at these temperatures reducing sugars and amino acids are added to the crust (as exemplified in this patent where dextrose and whey solids are used). Not so surprisingly there is also a patent on how to avoid excessive browning in cookies which calls for addition of a polycarboxylic acid ester to lower pH and hence slow down the Maillard reaction.

Pretzels are an extreme example of how the Maillard reaction can be tweaked. Before baking the pretzels are brushed with lye, a dilute solution of sodium hydroxide, which is very basic. The high pH speeds up the bottleneck of the Maillard reaction (see end of post for details).

A pinch of baking soda can bring out a new taste dimension when browning onions

Another basic ingredient found in most kitchens is baking soda (sodium bicarbonate, NaHCO₃). It’s used as a leavning agent which requires addition of an acid to function. Since it is a weak base, it can be used to increase the pH and hence the speed of the Maillard reaction, for instance when browning onions. This basic task, which isn’t always so easy after all, benefits greatly from a pinch of baking soda (and surprisingly it seems that this hasn’t been done before!). To illustrate this I’ve made a time lapse video of chopped onions being fried with and without baking soda. The frying took 11 min, but things are speeded up about 10x.

Samples taken throughout the experiment are shown in the picture below. Even after 4 min there is a visible difference. After 11 min, the small addition of baking soda has yielded onions which taste remarkably sweet with strong caramel notes, compared to the control which tastes like fried onions.

Another example of how baking soda is used to speed up the Maillard reaction is dulce de leche, a popular sauce/caramel candy in Latin America. It’s made by slowly boiling sweetened milk. Baking soda is not a required ingredient, but is often included. The baking soda gives dulce de leche a darker color and also contributes to the flavor.

Photo by audinou from flickr.com.

It should perhaps be added that baking soda is frequently used in Chinese cooking, for instance in tempura batters and marinades. Once there, the baking soda will certainly speed up the Maillard reaction, but it also affects the texture of meat – I’ll have to return to that topic later.

To round of this post I will briefly touch upon one of the reasons why pH influences the Maillard reaction. The first step involves a reaction between a reducing sugar (depicted as R(C=O)H) and an amino acid (depicted as R’NH2) followed by loss of water to yield a Schiff base. The Schiff base rearranges to the Amadori product (not shown). Of these first steps the formation of the Schiff base is the bottleneck (rate limiting step). The reactivity of the amino acid is influenced by the pH. A simplified reasoning goes like this: At low pH the amino group is protonated, yielding it less nucleophilic. At higher pH, the nitrogen becomes more nucleophilic and at very high pH the amino group can even be deprotonated. It should be noted that the fate of the Amadori product is also in large determined by pH and hence pH will affect more than just the rate, but this is far beyond the scope of this blog post.

But there is more to such a foam than trolls! For the following experiment, use one eggwhite and a berry syrup of your choice – I used a blueberry syrup (approximately 1,5 dL). Start by whisking the egg white. Add the syrup slowly over 5-10 min while constantly whisking. Observe how the volume increases dramatically. When I did the experiment I got roughly 2 L of foam (which corresponds to a 40-50 fold increase in volume). Make sure you use a clean bowl, preferably one of metal as fats and oil cling very well to plastic bowls.

Now comes the fun part: Put some of the egg white foam onto a plate and place it in a microwave oven to make the proteins set! Hervé This described this in a recent article and decided to name this dish “Vauquelin” after the french pharmacist and chemist Louis Nicolas Vauquelin. It does take some experimentation to find a proper combination of the power setting and the time needed for the Vauquelin to set. If you overdo it, the foam will just collapse. I used the 360W setting and 4 seconds for the Vaquelin in the picture below.

Cutting through the Vauquelin with a knife leaves a trace which does not refill.

Scooping out with a spoon also gives you an impression of the texture.

Instead of blueberry syrup you can try other liquids. Hervé This suggests orange juice or cranberry juice (both require addition of sugar). Liquours also work fine (although my experimentation suggests that the volume increases somewhat less), but remember to add sugar as this stabilises the foam and rounds of the taste.