When I blogged about DIY mineral water last year it was mainly a theoretical exercise since I didn’t have the required salts at hand. My experience was limited to adding some baking soda (sodium bicarbonate) to water before carbonation. Luckily Paul Hinrichs tested the calculator! In the meantime I have purchased the required salts and with several kilograms in total I’m probably well stocked for the next decade! Based on the output from the calculator, I mixed the salts required to clone San Pellegrino, added water and carbonated the mixture. And the good news is that it works! The water tastes great and I’ve been enjoying cloned mineral waters every day now for the last couple of weeks.

Some changes have been made to the mineral water calculator (Updated! – scroll down for download options) since I last posted:

• a simpler worksheet more suitable for printing has been added
• more mineral waters have been added to the database, covering TDS (total dissolved solids) levels all the way up to more than 4000 mg/L
• potassium bicarbonate, magnesium chloride and calcium nitrate are made optional and can be left out if desired (it’s still a little unclear to me to what extent these can be detected at the typical levels found in mineral waters)
• one can now chose between using either hydroxides or carbonates of calcium and magnesium, depending on availability (it should be noted however that some waters high in bicarbonate may require the use of the hydroxides – not quite sure about this though)

A spoon full of mineral salts is required for the preparation of 1 liter of San Pellegrino mineral water.

Instructions for how to prepare the mixture of salts
Start by chosing the mineral water you want to clone from the drop down list. My advice would be not to start with the waters having very high levels of total dissolved solids (TDS) (except Kessel and Vichy Saint-Yorre since sodium bicarbonate dissolves easily). Aim for a TDS in the range 200-1500 mg/L (the list of all mineral waters in the rightmost worksheet is viewable and sortable). At the lower end you may not detect much mineral taste at all. At the higher end the mineral taste becomes quite pronounced. You can click the check boxes to include/exclude some salts. If known enter the composition of your tap water (your local water company should be able to give you these figures). I suggest that you weigh out the salts for 10 or even 100 liters, otherwise the amounts of salts will be in the low milligram or microgram range, requiring expensive lab scales. Mix the salts well. It may be god to start by mixing the salts present in the lowest concentrations first to ensure a homogeneous mixture.

How to make a cloned mineral water
Weigh out the approximate amount of salt (prepared as described above) needed for the amount of water that your carbonation vessel holds. At this point it’s doesn’t need to be very accurate, so if you have weighed it once you can simply need to remember which spoon you used and the size of the heap. Note that the different mineral salts vary greatly in density, so you should calibrate the heap used for each mineral salt mixture. Add the salt to the carbonation vessel and fill it up to the mark with water. The water will now turn opaque and whitish as the salts are suspended in the water (see picture above). Carbonate carefully and, depending on whether the water is high in carbonation and/or bicarbonate, try to hold the carbonation pressure for a couple of seconds extra before letting the pressure out. This allows a little more carbon dioxide to dissolve. Screw on the cap immediately to prevent the carbon dioxide from escaping. In some cases it may be necessary to repeat the carbonation step after some hours. Once the salts have dissolved (i.e. the water becomes clear) you can enjoy your very own home-made mineral water!

Several of the mineral salts have are not soluble in tap water, hence the opaque look to the left. After carbonation however they dissolve rapidly.

So far I’ve made up the salt mixtures for San Pellegrino (total dissolved solids, TDS: 1109 mg/L) and Gerolsteiner (TDS: 2488 mg/L). The first works like a charm, even when all salts are added simultaneously. This is possibly due to the high amount of sulfates which seem to dissolve more easily. Gerolsteiner is more tricky, partly due to the high TDS and the low amount of sulfate. I made it using carbonates instead of hydroxides, hoping that this would require addition of less carbon dioxide to neutralize the base. But after two days and 2-3 extra additions of carbon dioxide the salts had still not dissolved completely and this puzzles me. I certainly need to repeat this experiment. Darcy O’Neil states in Fix the pumps that the order of addition does matter. I’m not quite sure if that really is the case as most of the salts have a very low water solubility to start with, and the carbonic acid is the reason they dissolve. But maybe there is something I’m overlooking here? It could be that Gerolsteiner is easier to do with hydroxides, but Paul Hinrichs also had some trouble getting all the salts to dissolve for Gerolsteiner.

Some of the salts may be tricky to obtain, but the synonyms and links to Amazon below may be of some help:

• CaSO₄·0.5H₂O = Plaster of Paris (check availability from Amazon)
• MgSO₄·7H₂O = Epsom salt (check availability from Amazon)
• CaCO₃ = Chalk (check availability from Amazon)
• NaHCO₃ = Baking soda
• NaCl = Table salt
• Mg(OH)₂ = Milk of magnesia (check availability from Amazon)
• Ca(OH)₂ = Slaked lime, pickling lime, CAL (check availability from Amazon)

Before you head of to Amazon or some other place to order salts I should probably add some words of warning: make sure that the source you find is suitable for consumption! Some technical qualities of mineral salts may not be intended for food use, for instance due to the presence of heavy metals or other contaminants.

Note that some of the salts are available with varying amounts of crystal water. If you use other salts than those specified (i.e. anhydrous salts or salts with more crystal water) the molecular weights in the spreadsheet need to be adjusted for this. I guess that if you are familiar with the concept of crystal water, you’ll easily figure out the correct molecular weight and how to update the calculator according to the specific salts you chose to use.

Screen shot of the simple version, best suited for printing (see below for download options):

Screen shot of the complete version (see below for download options):

Calculator download options
Version 5 (latest update)
Excel: mineral_water_calculator_v5.xlsx (44 kB)
Open office: mineral_water_calculator_v5.ods (44 kB)

Version 4 (the version originally provided with this blog post – contains errors)
mineral_water_calculator_v4.xlsx

Mineral waters included
Mineral waters included in the database that comes with the calculator: Acqua Panna, Antipodes, Apollinaris, Aquarel Birken, Artificial mineral water, Badoit, Borsec, Burton (beer brewing), Calistoga, Carola Rouge, Contrex, Dorna, Evian, Farris, Fiuggi, Gerolsteiner, Harghita, Hassia Sprudel, Henniez, Kessel, London (beer brewing), Mountain Valley Spring, Munich (beer brewing), Neuselters, Perrier, Pilsen (beer brewing), PurPur (coffee brewing), Rosbacher Klassich, Saint-Yorre, Salvus, San Benedetto, San Narciso, San Pellegrino, Selters, Tea brewing (max), Tea brewing (min), Tesanjski Dijamant, Ty Nant, Vittel, Volvic, Voss, Waiwera. And you can easily add data for other mineral waters. The websites mineralwaters.org, finewaters.com and Mineral water atlas of the world have data for several hundred waters available. And if you have a bottle of your favourite mineral water at hand you only need to check the label to find the required input for the calculator.

Talking to a friend last year who is an avid home brewer made me realize how little I knew about beer and brewing. Inspired by what I learnt from the conversation I started reading Palmer’s How to brew which is essential for starters, but soon I also turned to Brigg’s Brewing – Science and practice and Priest’s Handbook of Brewing which are more rewarding if you’re a scientist. The first two steps in brewing beer – mashing and wort boiling – are really quite sophisticated extractions. And there is a lot of chemistry involved, so brewing beer seemed to me like an obvious extension of all my other interests. This is also the reason why I wanted to include a post about brewing in the Wonders of extraction series. The pictures for this blog post were taken as I brewed and bottled my latest batch, an American India Pale Ale.

Having read quite a lot about beer I soon found myself in the kitchen brewing my very first German wheat beer in August last year. I had decided that to familiarize myself with brewing I would try to brew with whatever equipment I had available in the kitchen. Mashing and lautering was done with a pasta strainer(!), and I boiled the wort in the largest pot I could find. While doing this it became very clear to me that these steps can be viewed as “reactive extractions”. Something is extracted and then something more happens! Given the simple method and equipment used I was totally amazed by the end result. And I quickly decided that this would not be my last batch of beer. After hours or reading (and making an important decision that I would like to spend my time brewing, rather than building the equipment) I finally settled with a Speidel Braumeister. This is a compact RIMS (Recirculating Infusion Mash System) type brewery system where a pump forces the wort upwards through the malt bed (different from a conventional RIMS system where the wort is allowed to drain through the malt bed by gravity). The picture below probably explains more than countless words.

The Speidel Braumeister is a compact RIMS type brewing system. During mashing a malt pipe is inserted. A metal screen and filter cloth at both ends of the malt pipe hold the malt in place. A pump forces the wort upwards through the mash (bottom left). After mashing the malt pipe is lifted out to allow the wort to drip of (bottom middle). Extra water may be added to rinse out remaining wort. The malt pipe is removed prior to the wort boiling (bottom right). Illustrations taken from www.speidel-braumeister.de

What really attracted me to brewing is that the range of ingredients available to professional brewers is also available to home brewers. And while a commercial brewery will do what it can to cut costs, opting for cheaper ingredients whenever possible, the money spent on malt, hops and yeast doesn’t really matter that much for the home brewer. As a result one can actually brew some very nice beers at home. And a much larger range of beers than is available in your next door shop. I believe this is quite different from what is the case for home brewing of wine (at least in Norway where fresh grape juice in those quantities is not available).

The extraction of sugars from malted barley is termed mashing. During mashing one utilizes the enzymes naturally present in grains to break down the starch to fermentable sugars (meaning sugars that the yeast can convert to alcohol). It sounds simple, but the process involves a number of enzymes with different temperature and pH optima. And one needs to do a couple of tricks for the enzymes to appear, so I will start with a brief introduction to malting (but feel to skip this and continue reading about mashing further down).

Malting
When a barley seed is wetted it will start to germinate. The release of the plant hormone gibberellic acid in the seed embryo sets of the synthesis of proteins capable of breaking down starch to sugar which will be needed for the seed to grow. These proteins are called enzymes, and they are extremely efficient at breaking down starch to sugar. After a couple of days the sprouted grain is air dried. As the water content decreases a second plant hormone, abscisic acid, is released. The effect is the opposite of gibberellic acid, and the synthesis of further enzymes is halted. The lowered water content also stops the enzymatic breakdown of the starch. The air dried green malt as it is now called is further kiln dried. The small amount of liberated sugar alongside the proteins allows for the Maillard reaction to proceed if the conditions are right, resulting in characteristic malt and caramel flavors as well as colors ranging from golden to brown and almost black. The darker the color of the malt, the less will be left of the enzymes required for starch hydrolysis (but this is usually not a problem as only a relatively small amount of very dark malt is used). Some enthusiasts malt their own barley, but most home brewers buy whole grain malt.

The hopper of my malt mill filled with ~5 kg malt is ready for some action (top left). As the grains pass the two rollers (bottom left) the malt is carefully crushed (bottom right). If crushed too fine the result is a “stuck mash”, if crushed too coarsely less sugar will be extracted and the yield drops.

Bottom screen and filter cloth inserted into the malt cylinder (top left) which is then lowered into the water filled brewing pot, crushed malt is then poured into the malt cylinder (top right), covered with a filter cloth (bottom left) and a metal screen (bottom right).

Mashing
The malt now contains starch as well as the enzymes required to break down the starch. When water is added and the temperature brought up to around 65-67 °C the enzymes start doing their job which is to break down the starch to sugars. This step is called mashing. Several enzymes are at play, but I’ll focus on the two most important: alpha-amylase and beta-amylase. Alpha-amylase is more temperature stable, attacks and breaks up the starch polymer at random places, resulting in smaller starch molecules known as dextrins. Only a very small fraction of the starch is converted to fermentable (= usable for the yeast) sugars by alpha-amylase. Beta-amylase on the other hand is less temperature stable but breaks down starch to maltose which is fermentable. By carefully choosing the mashing temperature the relative activity between alpha- and beta-amylase can be fine tuned. Mashing at 64-65 °C favors beta-amylase which yields a wort higher in fermentable sugars, resulting in a beer which is thinner, drier, higher in alcohol and has a lower final gravity. Mashing at 68-69 °C favors alpha-amylase which yields more dextrins which are not fermentable, resulting in a beer with more body which is sweeter, lower in alcohol and has a higher final gravity (i.e. residual “sugar” content). This may be confusing but trust me – it’s even more confusing when John Palmer tries to explain it with a garden allegory! I encourage you to check out the figure below which may help clarify things.  After mashing is complete the temperature is increased to 78 °C to inactivate the enzymes. The malt pipe is then pulled up to allow the wort contained in the malt bed to run off (termed lautering). The malt bed may be washed with 78 °C water (sparging) to increase the yield.

The wort is circulated upwards through the malt bed throughout the mashing time. At first the wort is very cloudy (top left) due to the fine particles from the crushing. The malt bed acts as a huge filter which helps remove particles, yielding a clear wort (top right). The time and temperature steps are controlled by a PID (bottom left). After mashing the malt cylinder is pulled up, the wort is allowed to run off (termed lautering) and the malt bed may be washed with water (sparging). The malt that remains is known as wet distillers grain (bottom right) and does wonders to your compost! Or you can use some of it for baking a special bread called treberbrot (named after the German word for spent grain).

If the extractable yield of a malt was 100% and the mash efficiency was 100% 1 kg malt would yield 1 kg of sugar in the mash. However, the extractable yield for a pale malt is about 80% (the hulls for instance are not extractable), and in my last brew I reached a mash efficiency of 78%. In effect I got approximately 624 g of sugar for each kg of malt.

Wort boiling
After mashing and lautering the wort is heated further and kept at a rolling boil for about one hour. There are several reasons for this. First the mashing enzymes are destroyed. Another one is to sterilize the wort (i.e. kill off unwanted bacteria and yeasts) prior to the following fermentation. Furthermore the boiling will allow some unwanted volatiles such as dimethyl sulfide to escape. The boiling will also facilitate the precipitation of proteins, resulting in a clearer beer. But perhaps most important for the resulting taste of beer is the addition of hops to the boiling wort. Hops are a kind of flowers that impart a bitter taste and in some cases also a significant aroma to beer. The bitterness balances the sweet taste of the wort, and the hops also stabilize and increase the shelf life of beer due to a mild antibiotic effect against bacteria that could otherwise ruin the beer.

Hops are typically added as whole cones or pellets as shown here. The pellets are crushed hop flowers that have been compressed for easier addition. Once added to the wort the pellets fall apart. The larger surface area of the fines results in a faster extraction of the alpha acids.

The hop cones contain alpha acids which are not particularly water soluble, and in fact not very bitter either. But when boiled they undergo a chemical change which makes them more bitter, the so called isomerization (shown below). Hops that are added for bittering of beer are typically added to the wort once it starts to boil as the extraction and isomerization processes takes some time. The extraction of alpha acids and the isomerization process are well studied and brewers can accurately predict and design the bitterness of a beer using online calculators. Required input data are wort volume, wort gravity (i.e. sugar content), alpha acid content in the hops and boil time as well as whether the hops are added as whole flowers or as fines compressed to a pellet. The hop bitterness is expressed in International Bitter Units (IBU), typically ranging from light lagers or wheat beers with 5 IBU up to India Pale Ales with 100 IBU or more. Those with access to a spectrophotometer can measure an approximate IBU of a beer by recording the absorbance at 275 nm and multiplying the number by 50 (IBU = A₂₇₅ x 50).

In addition to alpha acids hops also contain essential oils, some lighter, more volatile (primarily terpenes such as myrcene, linaol, geraniol, limonene, terpineol etc. – typically with a citrusy, green, grassy, floral aroma) as well as some heavy, less volatile oils (humulene, caryophyllene, farnesene – typically with a woody, spicy aroma). When smelling fresh hops it’s primarily the essential oils that make up the aroma. The majority of volatiles are lost from the boiling wort due to evaporation. However, if hops are added towards the end of the boil the less volatile oils will remain in the wort and in the resulting beer and impart a significant hop aroma to the beer (not to be confused with the bitter taste which results from prolonged boiling of hops). In some cases hops are even added to the wort during of after fermentation, so called dry hopping. This allows the extraction of the lighter volatile essential oils in the hops. In order to capture the lightest volatile oils it’s important to use fresh hops (i.e. hops that have not been dried). To complicate matters further many of these essential oils are quite reactive towards oxygen, and if digging deeper into the molecules behind a “hoppy” aroma one will find several oxidation products of the essential oils.

Here I should add that chefs probably could learn something from the early and late addition of hops to the boiling wort. I have a feeling that the early vs. late addition of spices and herbs has not yet been explored sufficiently. And just like the same hop contributes different “fractions” of its flavor depending on when it is added I also think that spices and herbs could contribute a broader range of aromas if they were not added all at once. I would be very interested in hearing your opinions on this! And hereby I also share an idea for a nice science project: Boil herbs/spices, take samples regularly and see how concentration changes with time. When does it reach a maximum? This would be very useful information for chefs!

The wort is boiled (top left) for several reasons, one is to extract and isomerize alpha-acids from hop cones into iso-alpha-acid which provide the important bitterness to beer. After boiling cold water is passed through a copper spiral (top right) to rapidly cool the wort (bottom left). After cooling the gravity (i.e. density) of the wort may be measured with a hydrometer (bottom right).

Towards the end of the wort boil some brewers also add some Irish moss to help clarify the wort. Interestingly this moss should be well known to the readers of Khymos, albeit in a slightly different form – namely as a white powder sold under the name carrageenan!

Dry Irish moss contains more than 50% of the polysaccharide carrageenan. When used in brewing the moss is wetted and allowed to hydrate before it is added added to the boiling worth the last 10-15 min.

The rest of the brewing process does not involve extractions, and hence is not the main focus of this blog post. But I’ve included some pictures to give you an idea of the different steps:

The cooled wort is sprinkled (top left) into the fermentation bucket to expose it to oxygen. For extra oxygenation an aquarium air pump can also be used to aerate the wort, resulting in some foam (bottom left). The added oxygen allows the approximately 100 billion yeast cells (top right) to grow/multiply before they move into anaerobic mode to produce ethanol from the wort sugars (primarily maltose). Proteins and hop residues are carefully left behind in the boiling vessel (bottom right).

Clean bottles are covered with aluminum foil prior to dry sterilization (top left). The fermented (and in this case dry hopped wort) is siphoned (top right) into a second bucket where it is mixed with the priming sugar need for bottle carbonation. The bottling device used here (bottom left) has a small valve which only opens once the bottom of the bottle presses against it, thereby reducing foaming during bottling. Labels are glued onto the bottles with milk.

After a minimum of 1-2 weeks bottle fermentation the American India Pale Ale is sufficiently carbonated for the very first tasting!

Previous blog posts on the Wonders of Extraction
Wonders of extraction: Water
Wonders of extraction: Ethanol
Wonders of extraction: Oil
Wonders of extraction: Espresso (part I) (sorry – no part II yet…)
Wonders of extraction: Pressure

The lecture schedule for the 2011 fall semester is as follows (exact dates and locations here):

1. Historical Context and Demos Illustrating the Relationship of Food and Science. Speakers: Dave Arnold (Food Arts magazine’s Contributing Editor for Equipment & Food Science), Harold McGee (author of On Food and Cooking: The Science and Lore of the Kitchen and columnist for The New York Times) and David Weitz (Mallinckrodt Professor of Physics and of Applied Physics at Harvard)
2. Sous-vide Cooking: Phases of Matter. Speaker: Joan Roca (El Celler de Can Roca).
3. Heat and Temperature Flux in Chocolate. Speaker: Ramon Morató (Aula Chocovic)
4. Viscosity and Thickeners. Speaker: Carles Tejedor (Via Veneto), Fina Puigdevall and Pere Planagumà (les Coles)
5. Food Texture and Mouth Feel. Speaker: Grant Achatz (Alinea)
6. Gelation. Speaker: José Andrés (ThinkFoodGroup, minibar, Jaleo).
7. Emulsions: Traditional and New Emulsions. Speaker: Nandu Jubany (Can Jubany) and Carles Gaig (Fonda Gaig).
8. Proteins & Enzymes: Transglutaminase. Speaker: Wylie Dufresne (wd~50).
9. Browning Reactions: Culinary Examples. Speaker: Carme Ruscalleda (Sant Pau, Sant Pau de Tòquio).
10. Molecular Differences Between Production Methods. Speaker: Dan Barber (Blue Hill).
11. (Title to Come) Speaker: David Chang (momofuku)
12. Heat Transfer. Speaker: Nathan Myhrvold (former Microsoft CTO; co-founder and CEO of Intellectual Ventures; and author of Modernist Cuisine: The Art and Science of Cooking)
13. Dessert. Speaker: Bill Yosses (White House)
14. Technology and Cooking. Speaker: Ferran Adrià (elBulli)

Below is the 2010 schedule for comparison. Remember that all of these are available on Youtube and iTunes!

1. Science and Cooking: A Dialogue. Speakers: Harold McGee, Ferran Adria (elBulli), José Andrés (minibar by josé andrés, Jaleo, The Bazaar) with commentary/moderation from Professors David Weitz and Michael Brenner (Harvard).
2. Sous-vide Cooking: a State of Matter. Speaker: Joan Roca (El Celler de Can Roca).
3. Brain Candy: How Desserts Slow the Passage of Time. Speaker: Bill Yosses (White House Pastry Chef).
4. Olive Oil & Viscosity. Speaker: Carles Tejedor (Via Veneto).
5. Heat, Temperature, & Chocolate. Speaker: Enric Rovira.
6. Reinventing Food Texture & Flavor. Speaker: Grant Achatz (Alinea).
7. Emulsions: Concept of Stabilizing Oil &Water. Speaker: Nandu Jubany (Can Jubany).
8. Gelation. José Andrés (ThinkFoodGroup, minibar, Jaleo).
9. Browning & Oxidations. Carme Ruscalleda (Sant Pau, Sant Pau de Tòquio).
10. Meat Glue Mania. Wylie Dufresne (wd~50).
11. Cultivating Flavor: A Recipe for the Recipe. Dan Barber (Blue Hill).
12. Creative Ceilings: How We Use Errors, Failure and Physical Limitations as Catalysts for Culinary Innovation. David Chang (momofuku).

In case you didn’t know the current world record for the world’s fastest ice cream is 10.34 seconds! To obtain the record you have to make one liter of ice cream from milk, sugar and flavoring (no eggs). Liquid nitrogen is used to rapidly cool and freeze the ice cream mixture. The current record was achieved by Andrew Ross (UK) at Cliffe Cottage in Sheffield,​ South Yorkshire,​ UK, on 6 June 2010. Prior to that the world record belonged to Peter Barham who in 2005 shaved two seconds of his previous record, ending at 18.78 seconds. To conclude his presentation on how food can be used to make students interested in physics and chemistry Peter decided to beat the current world record. Here’s a video of how it went:

Want to read more about the history of liquid nitrogen ice cream and find recipes? Then you should visit the webpages of The institute for liquid nitrogen ice cream experimental studies!

Peter Barham’s presentation at the MG seminar in Copenhagen focused on how food can be used to make students interested in physics and chemistry (not a bad thing, especially since 2011 is the International Year of Chemistry) -Most people think science is boring and difficult, he said. But demos can help bring science to life, and believe it or not – experiments are much better when they go wrong. Using balloons, champagne, potatoes and liquid nitrogen Peter Barham proved his point. As an example he asked the audience how much air weighs. He first filled a balloon with a few milliliters of water, then squeezed out all the air, tied a knot and heated the water in the microwave until all had evaporated. The first balloon exploded since he used to much water (this shows that water expands when boiled and that balloons are not infinitely stretchable!). Using a little less water for the second balloon, everything worked fine. Assuming that steam has approximately the same density as air, the size of the balloon can be measured and from this the weight of air be calculated. One finds that the volume of the water increases by a factor of approximately 800x.

There will be more foam when champagne is poured into a dirty glass due to more nucleation sites providing the dissolved carbon dioxide with more escape routes.

Ever heard about how a spoon in the neck of an opened champagne bottle can keep the champagne fizzy? Well unfortunately this is a kitchen myth. The only thing that helps is keeping the bottle cold. The spoon has no effect whatsoever. And the balloon once cooled can help illustrate this. When all the steam had condensed there was a significant amount of gas left in the balloon (remember that all the air was squeezed out to start with). This illustrates that gases are soluble in water at low temperature, but not at higher temperature. When water is boiled the gas escapes. Gas (and in particular carbon dioxide) is more soluble at lower temperatures, and that is the explanation why champagne may retain quite a lot of the fizz if stored cold. The spoon is only there to confuse you!

How long does it take to boil a potato?

Next question was: How long does it take to boil potatoes? Since the visual appearance of a potato changes around 60 °C it is possible to monitor heat transfer by simply slicing a potato in two. If boiled in water a nice ring with a slightly darker color indicates how the heat travels uniformely towards the center. If you plot the width of the ring against the square root of the time you get a nice straigth line. However, if heated in a microwave a different pattern emerges. The wavelength of microwaves is on the order of several centimeters and as a consequence the distance between hot and cold areas are about 2 cm. Slicing a microwaved potato shows how only one side has been heated. This is the simple reason why food heated in a microwave oven must be left to stand for a while to allow the heat to diffuse.

When heated in boiling water the heat travels uniformly towards the center of the potato as evidenced by the “ring” that occurs once the temperature reaches 60 °C.

When heated in a microwave there will be hot and cold areas as illustrated with this potato.

Peter Barham also mentioned the experiment that demonstrates the difference between taste and aroma. If you close your eyes, hold your nose and have a friend give you either a piece of apple or pear, you’ll have a difficult task saying which is which. But the second you let go of your nose you recognize what you have in your mouth. The experiment can also be conducted with lemon and lime or other fruit pairs with similar textures. The reason for this is that when you hold your nose, hardly any air from the mouth will enter your nose through the retronasal passage. As a result you will not be able to “smell” what’s in your mouth. But the second you let go of your nose, air can pass freely and you immediately smell what’s in your mouth. This is also the reason why the aroma of food is subdued if you have a cold and a runny nose.

Close your eyes, hold your nose and experience the difference between taste and smell! Apples and pears taste remarkably similar when the aroma is blocked out by holding your nose.

Peter’s last demonstration was liquid nitrogen ice cream and an attempt to break the current world record of 10.34 seconds. More on that in the next post

My immersion circulator is working again! And the first thing I decided to do was to cook eggs at 63.0 °C for 40, 60, 75, 110 and 155 min and show you the results. If you read my last blog post on Perfect egg yolks or have stumbled across the paper Culinary Biophysics: on the Nature of the 6X°C Egg you may recognize that these times correspond to egg yolks with textures similar to sweetened condensed milk, mayonnaise, honey, cookie icing and Marmite respectively. I used the iso-viscosity graph from the paper mentioned to determine the cooking times as shown below.

The figure shows how cooking times at 63.0 °C are determined to achieve different textures. (The figure is used with kind permission from Springer Science+Business Media: César Vega and Ruben Mercadé-Prieto in Food Biophysics 2011, 6:152-159, Culinary Biophysics: on the Nature of the 6X °C Egg, figure 8, page 158. The legend overlay has been added by me for clarity.)

As the individual eggs reached their cooking times they were held in cold water until the last egg was finished. I then cracked all the eggs and took the pictures below to illustrate the differences in textures. I think the picture speaks for itself. The amazing thing is that the only difference between the eggs is the cooking time!

It can be difficult to judge textures properly from still photos, so I also shot a few video clips to illustrate the texture of the 40, 75 and 155 min eggs (by the time I shot the videos the yolks had become more viscous, possibly due to cooling and/or evaporation). The texture ofthe 155 min egg yolk was perhaps the most fascinating with a tremendous plasticity. There must be some exciting culinary uses for this!

If an egg is to be served by itself one will typically also want to set the white. There was a question about this to my previous post, and a reader even tried with 2 min pre- or post-boil. Without cooling the difference between pre- and post-boil was quite significant as evidenced from the pictures. I did a similar experiment but cooked the eggs at 63.0 °C and opted for a 3 min pre- or post-boil with the small difference that I cooled the egg back to room temperature after/prior to the pre-/post-boil to avoid any interference between the 63 °C and 100 °C treatments. This worked very well and I wasn’t able to detect any difference between the pre- and post-boiled eggs.

It doesn’t matter if you pre- or post-boil your egg as long as you cool it to room temperature inbetween the boiling water and the temperature controlled water bath.

In 2009 I wrote about my journey towards the perfect soft boiled eggs. Equipped with a formula I knew what I wanted, but it wasn’t so easy after all. Since then I’ve tried to model experimental data from Douglas Baldwin as well as data from my own measurements of egg yolk tempereatures when cooked sous vide (pictures of how I did this at the end of this blog post). I never got around to blog about the results, and now there’s no need for it anymore: The egg yolk problem has been solved! And the question that remains is: How we can utilize this in the kitchen?

The break through came this year with a paper by César Vega and Ruben Mercadé-Prieto entiteld Culinary Biophysics: on the Nature of the 6X°C Egg [1]. In my opinion it’s a brilliant example of molecular gastronomy: the results are practical enough for chefs and technical enough for scientists. This paper holds the key to unlock the true potential of egg yolk texture, and with it every chef can reproducibly prepare yolks with textures in the whole range between soft and hard. If you think I sound a bit exalted, you’re absolutely right.

Eggs cooked at low temperature have been all around the internet for the last couple of years, but a general feature of all these posts has been a focus on temperature. This has been the generally accepted truth. Even Hervé This in an interview with Discover magazine claimed that “Cooking eggs is really a question of temperature, not time”. But the present paper counters this. It’s main conclusion is that the texture of the egg yolk is a result of the time-temperature combination used, it’s thermal history if you like. If you’re interested in the details of the paper I suggest you jump directly to the pdf (I could download it for free some days ago, so give it a try), but if you’re only interested in the results, read on! A practical way to measure egg yolk texture is by using a rheometer. It’s a fancy piece of equipment that measures viscosity (and for those of you who are technically inclined – it measures viscosity as a function of shear rate). And what César and Ruben have done is to prepare a graph that shows the viscosity of a large number of temperature and time combinations. It’s a so-called iso-viscosity plot, meaning that once you have decided which viscosity you want the graph will show you all the temperature-time combinations that will give the desired result.

The figure shows how an egg yolk with a texture resembling one of the reference foods can be prepared by chosing any temperature-time combination along the respective plotted lines. (The figure is used with kind permission from Springer Science+Business Media: César Vega and Ruben Mercadé-Prieto in Food Biophysics 2011, 6:152-159, Culinary Biophysics: on the Nature of the 6X °C Egg, figure 8, page 158. The legend overlay has been added by me for clarity.)

For chefs, and even for chemists not working with rheology, it’s difficult to relate to numerical values of viscosity. To get around this the authors did a clever thing by measuring the viscosity of a range of semi-solid foods that may function as reference points: sweetened condensed milk, mayonnaise, honey, cookie icing and Marmite. You can use the iso-viscosity plot shown above to find different time-temperature combinations that give the same yolk viscosity. To use the plot, first decide which texture you want the egg yolk to have. Let’s say you’re in for a honey like texture (filled triangles). Pick a temperature, draw a vertical line until it crosses the line plotted through the triangles and then a horizontal line from there to the time axis. Repeating the exercise for different temperatures will give the different time-temperature combinations that all give a honey like yolk texture; in this case 310 min at 60 °C, 200 min at 61 °C, 125 min at 62 °C, 75 min at 63 °C, 55 min at 64 °C, 45 at 65 °C, 40 min at 66 °C, 26 min at 67 °C and finally 25 min at 68 °C will all do the trick. With a temperature controlled water bath one can chose whatever combination one likes, but if using a large pot of water and manually turning the heat on/off it’s advisable to cook the egg yolk in the lower temperature range. Also, the authors state that it requires a bit of practice to obtain different textures at temperatures above 66 °C.

The paper only deals with egg yolks. At the given time-temperature combinations the white will remain more or less runny. If only the yolk is to be used this doesn’t matter. But if serving the whole egg a simple way to set the egg white is to immerse the egg in boiling water for 2-3 minutes. Alternatively for a little longer at 85 or 90 °C. A comment made by Olly Rouse to my previous post on eggs suggests 8 min at 90 °C followed by cooling at 55 °C is perfect to set the white. However, if the eggs are to be “cooled” at 6X °C maybe 6-7 min is enough. What complicates matters even more is that at 6X °C convection inside the still runny egg white contributes significantly to the heat transfer, but I assume that this is negligible in combination with the longer cooking times in the lower 6X °C range.

Now that all possible egg yolk textures are available the question is: How we can utilize this in the kitchen? Apart from preparing soft boiled eggs, are there any applications in cooking? I’m sure there are many good ideas out there just waiting to be realized. If you blog or twitter about your ideas for utilizing precisely cooked egg yolks I suggest that you tag your blogposts with 6Xyolk and your tweets with #6Xyolk. Then everyone can easily follow up on the progress.

From my own experiments with measuring the core temperature of eggs cooked sous vide: The pictures show how I cut a thin slice from a plastic wine cork, pierced it with a philips screw driver, glued it to an egg, carefully pierced the egg shell with the same screw driver and finally introduced a thermocouple into the core of the egg yolk. There was enough friction between the thermocouple and the wine cork to allow the egg to be suspended by the thermocouple in the water bath. Temperature was logged using myPClab from Novus. Prior to the measurement the egg with the inserted thermocouple were left for several hours in the fridge for temperature equillibration.

[1] Vega, C.; Mercadé-Prieto, R. Food Biophysics 2011, 152-159. DOI: 10.1007/s11483-010-9200-1

Sample #4: Precious instant coffee with hot and freezing milk. My favorite!

As part of the molecular gastronomy seminar in Copenhagen a group of food science students and aspiring chefs who meet regularily in Gastronomisk legestue (= gastronomic playroom) gave a short presentation of their work. With a yearly budget of €660 and no scientific or commercial obligations the goal is to let science and craft meet in order to foster culinary creativity. There are many notable chef-scientist collaborations in the realms of molecular gastronomy and modernist cuisine, but this is the first time I’ve heard about an initiative that establishes a dialogue between scientists and chefs while they are still students. Molecular gastronomy will always be an interdisciplinary field and what better way to encourage such a collaboration than in a “playroom”? The students are allowed to use course labs at Copenhagen University, and in return they are asked to do a least one event each year – in 2010 they contributed to Kulturnatten (= Culture night). I admire the initiative and I encouraged Mathias Skovmand-Larsen, one of the founders, to start blogging so the rest of the world can take part in their experiments. Their presentation included 4 samples for the audience to taste. My favorite was the coffee with hot and freezing milk topped with freeze dried coffee. And this was not any freeze dried coffee – it was very good coffee from the Coffee Collective in Copenhagen prepared with an Aeropress and then freeze dried! The freezing milk was in the form of ice cream. Very delicious!

Mathias Skovmand-Larsen holding a glass of sample #1: Birchwood sap and distilled amber. Interesting taste, but only as a base for something more.

Sample #3: Chicken under pressure and horseradish. The chicken had been treated (and sterilized) at 6000 bar. Compared with the pressure treated seafood at The Flemish Primitives in 2010 which retained a very raw character the appearance and texture of the chicken was more like cooked chicken.

Sample #2: Lumbsucker eggs and crispy full grain bread, designed for maximum texture contrast.

Michael Bom Frøst addressed complexity in meals based on experiments done at noma

What’s in a meal? – The title of associate professor Michael Bom Frøst‘s presentation at the recent seminar on molecular gastronomy in Copenhagen may seem surprisingly simple, but it turned out that a main topic of his presentation was in fact complexity and how it influences the meal experience. Together with PhD student Line Holler Mielby he conducted experiments in a real restaurant setting and given that the experiment took place in noma‘s chambre séparée and that some of noma’s chefs helped out in the kitchen you can imagine how easy it was to find volunteers. Previous studies have suggested a correlation between complexity and liking following an inverted U-shaped curve, suggesting that there is an optimum amount of complexity for maximum pleasure as shown in the figure below [1]. The main purpose of the experiment was to test this hypothesis. The theory also suggests that due to the exposure effect, diners who often eat “complex” food at high end restaurants would prefer more complexity compared to people who eat high end food less often. To address this question it was made sure that the test group included people with and without experience of high end restaurant food.

Wundt/Berlyne curve showing expected correlation between complexity and liking. The experiments were designed to test this hypothesis.

It is not easy to define what complexity means, but despite attempts at splitting the term up it seems that good results have been obtained simply by using the word complexity as is. In the previous study Expectations and surprise in a molecular gastronomic meal by Mielby and Frøst the complexity of the presentation was studied [2]. In this experiment the complexity of the food was varied. In the design of the experiment this was perhaps the most challenging part, as Michael Bom Frøst admitted that intended complexity did not always correspond with perceived complexity.

Despite the difficulty of defining complexity, the term is often invoked by chefs, both as something to strive for and something to avoid. Statments such as “primary flavors often depend on secret ingredients to make them more interesting and complex” (Michael Roberts), “less is more” (Gordon Ramsey in a comment to an over complicated dish in one of his TV shows) and “simplicity” (term used in the Manifesto for the New Nordic Kitchen) all allude to different levels of complexity.

To make a long story short, the real complexity-liking curve was not a U-shaped curve, but rather a steadily increasing curve which flattens out as shown below. - Maybe we really like complex dishes, says Michael Bom Frøst. The results also showed that experience level of the diners had no influence on the curiosity, surprise, novelty or complexity responses. However, hedonic/liking and familiarity received higher scores from the this test group. One further conclusion was that novelty is a better predictor of liking than complexity in high end dining.

The real complexity-liking curve differs from that predicted by Wundt/Berlyne in that there is noe decrease in liking as complexity increases. – Maybe we really like complex dishes, says Michael Bom Frøst.

Translating the results into a more popularized format, Michael presented the following “Recipe for the best meal experience”:

Further reading
Website with descriptions of experiments in 2008 and 2010 (in Danish only) as well as pictures of dishes served in 2007, 2008 and 2010
Expectations and Surprise in a Molecular Gastronomic Meal (pdf), presentation given by Line Holler Mielby at Eurosense 2008

References
[1] Berlyne, D. E. 1970. Novelty, Complexity, and Hedonic Value. Perception & Psychophysics 1970, 8 (5A), 279-286.
[2] Mielby, L. H.; Frøst, M. B. Food Quality and Preference 2010, 213. DOI: 10.1016/j.foodqual.2009.09.005. (subscription required)

Pia Snitkjær’s thesis on Investigations of meat stock from a molecular gastronomy perspective can be downloaded free of charge. Part I includes an excellent introduction to molecular gastronomy, part II covers meat stocks with and without red wine.

Pia Snitkjær was the first student in the molecular gastronomy project at the University of Copenhagen to complete her studies. She defended her PhD thesis on Investigations of meat stock from a molecular gastronomy perspective in December last year, and this was also the topic of her presentation at the recent seminar on molecular gastronomy at the University of Copenhagen. Meat stock is typically prepared by boiling meat, bones, vegetables, spices and herbs, and after straining the remaining liquid it is reduced in volume by further boiling. The central question in the thesis was how the reduction affects the flavor and texture of the stock. Cookbooks only specify the concentration factor, but not the time needed to achieve this reduction.

If you’re only interested in the conclusion from a gastronomic perspective the take home message was that the reduction time has a significant impact on flavor. For more flavor you want to do a slow reduction over low heat (see illustration below). But you should not overdo it as this will result in bitter and burned flavors. A reduction time of 15-20 hours seems to be optimal. The simple explanation is that with a high power input volatiles evaporate from your stock pot before they have time to react to generate new flavors (for instance in Maillard type reactions).

Figure from Pia Snitkjær’s thesis showing the effect of the reduction time on the aroma concentration of the resulting stock (Copyright Pia Snitkjær, used with permission)

Pia’s thesis (free download, 0.7 Mb) has two parts. The first is an introduction to molecular gastronomy, and frankly this is the best introduction that I’ve read to date on molecular gastronomy! The second part covers preparation of meat stocks with and without red wine.

Pia did two sets of experiments to arrive at these conclusions. In the time experiment she prepared stocks with concentration factors (CF) ranging from 2-12 as a function of the reduction time (3-36 h). Studying the volatiles she found that they fell into three categories:

1. Decrease: 2-pentanone and 2-propanone (boiling points: 101-105 °C, 57 °C)
2. Increase up to 15-20 h followed by decrease: 1- butanol and nonanal (boiling points: 118 °C, 195 °C)
3. Increase: acetic acid and 3-methyl butanal (boiling points: 118 °C, 91-93 °C)

The boiling points illustrate that category 1 is driven off fast due to lower boiling points whereas category 2 will evaporate very slowly (and possibly only be removed through an aerosol). The last category has lower boiling points suggesting that these compounds were not present from the beginning and are only formed after an extensive reduction.

Similarily she observed the following flavor changes of the same time span:

1. Decrease: boiled meat, nutty, sweet flavor
2. Increase up to 15-20 h followed by decrease: tar, roast crust
3. Increase: bitter, burned, sour, astringent

In the power experiment she studied the effect different power inputs (corresponding to reduction time of 4-30 h) have on a stock reduced to the same concentration factor. The resulting flavor profiles were very different with a key result being that a high power input results in a rapid loss of volatiles. A slower reduction leaves more time for new flavors to develop. Further details can be found in the thesis and in the paper Flavour development during beef stock reduction [1].

Pia Snitkjær presenting her results at the recent MG seminar in Copenhagen

There was no time to go into details of her second research paper on red wine in stocks, but the results have been published: Beef stock reduction with red wine – Effects of preparation method and wine characteristics [2]. An important finding was that wine and stock should be reduced together, not separately – this diminished the astringency from the tannins, most likely due to precipitation of insoluble protein-tannin complexes (just like the ones which make Norwegian egg coffee easy to drink). Furthermore it was shown that the initial differences in the aroma profile of the wines was partly eliminated by boiling. The choice of wine however still had an impact on the resulting flavor because the non-volatiles such as sugars, acids and phenolics of a wine did influence the end result. More specifically a reduced stock made with Zinfandel had bread, herb, wine-vinegar and chicken notes whereas a reduced stock made from Cabernet Sauvignon was dominated by beef and onion odors accompanied by a “salt taste and a significantly higher intensity of particulate mouthfeel and bitter taste”.

[1] Snitkjær, P.; Frøst, M. B.; Skibsted, L. H.; Risbo, J. Food Chemistry 2010, 645. DOI: 10.1016/j.foodchem.2010.03.025

[2] Snitkjær, P.; Risbo; J.; Skibsted, L. H.; Ebeler, S.; Heymann, H.; Harmon, K.; Frøst, M. B. Food Chemistry 2011, 183. DOI: 10.1016/j.foodchem.2010.10.096