It should come as no surprise that food, chemistry and mathematics meet in baking. For once I will leave the chemistry aside for a while and turn to the mathematical aspects of baking. More precisely I will delve into geometrical problems encountered in baking. When cutting cookies from a rolled out dough or placing cookies on a sheet for baking you actually attempt to solve a mathematical problem known as a packing problem. The purpose is to maximize the distance between the cookies and maximize the size of the cookies, paying attention that the cookies should not touch. Many will perhaps start with a square packing (see below), but soon figure out that a hexagonal packing will fit even more cookies onto the rolled out dough or onto the baking sheet (especially when the dough/sheet is large compared to the cookies). The optimum way of placing 2-17 circles in a square are shown below (and the solution for up to 10.000 circles is also available).

My challenge for you however is a different one as I’m interested in eliminating the leftover dough when cutting cookies. To achieve this the cookies cannot be circular. Using a square cookie cutter (or simply a knife) would be the easiest way to leave no gaps, but how cool are square cookies? What I’m really looking for are cookie tessallations which are aesthetically pleasing, and at the same time transferable to a baking sheet. Oh yeah: a tessallation “is the process of creating a two-dimensional plane using the repetition of a geometric shape with no overlaps and no gap” according to Wikipedia. So – no gaps – no leftover cookie dough!

Should you ever want to place circular cookies on a square baking sheet, this is how to maximize the size of the cookies! (Illustrations CC-BY-SA by Toby Hudson)

This is one way of solving the problem with leftover dough shown in the top picture. A tree can quite easily be transformed into a shape that fills the plane without any gaps. This image was made using the Tess software mentioned below.

Tessellations are frequently encountered in the art of M. C. Escher, and his Regular Division of the Plane Drawings are all based on tessellations. Most of Escher’s drawings however are not useful for making cookies because they are too interlocking – it would be impossible to take the cookies apart and transfer them to the baking sheet (and baking them “interlocked” would not be an option as cookie dough inevitably will raise/expand a little, making everything stick together). But I did find one example of an Escher inspired cookie cutter as well as some other nice examples of cookie cutters especially designed to make tessellations:

Over at Thingiverse the design file for this Escher inspired cookie cutter can be downloaded (Photo by Bas Pijls via Thingiverse). And should you want to transfer your own designs into a 3D printable format, check out this cookie-cutter-generator.

From Cox & Cox you can buy this Jigsaw cookie cutter (Photo from Cox & Cox product page). If you have access to a 3D printer you can also print your own jigsaw cookie cutter.

These elaborate cookie cutters are designed by Keith Kritselis. Over at Kickstarter you can find more information about his special cookie cutters for Halloween and Christmas. What makes them special is that each tessellation is made up of three or four different shapes.

If you rather want to make your own tessellations there are a couple of different software and online apps available, but I’ve found Tess to be one of the best. An evaluation copy of Tess (no save function) can be downloaded for free. Below are a couple of designs I’ve made. The patterns are nice, but would I want to each cookies with these shapes?

And finally the challenge for you all: Make your own cookie tessallations and share it! It’s not a competition, but rather an invitation to contribute. If the design is great I might have it 3D printed on a friends MakerBot or order it in metal from Shapeways and blog about it here If you send me a picture (preferably at least 620 pixels wide/high, email to webmaster/a/khymos.org) I’ll put up a gallery to display the submitted designs.

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.

My fellow bloggers Anu Hopia (Molekyyligastronomia) and Erik Fooladi (Fooducation) together with Jenni Vartiainen and Maija Aksela have embarked on a collaboration project to explore claims about food and cooking. If you are a researcher (from any field), teacher at any level, chef or simply a foodie who finds this interesting you can find info at the end of this email on how to contact them. I bring here their description of the project in extenso:

Interdisciplinary network of culinary claims
Is it true that you mustn’t rinse, but rather brush, mushrooms? Should a steak be seared to keep the juices inside? Can you prevent fruit salad from turning brown by sprinkling it with lemon juice? Such apparently mundane questions have been source of inspiration for food geeks at least since “The Curious cook” by Harold McGee (1990) was published, but most likely much earlier. A closer analysis of such questions reveal an abundance of intriguing, surprisingly complex and unexplored questions which might be vehicles for education and even subject for research within natural and social sciences.

The world of food and cooking is full of statements on how to do things and occasionally why one should adhere to these advices. Many are rooted in tradition or are created today by us all and sometimes appear to us like modern urban stories. Some are rooted in long experience of kitchen professionals or home cooks, and some even in science. When tradition and science meet interesting things might happen. In some cases the phenomenon in question (see examples in the introduction) is well described within one field of science but is less so in another discipline, laying questions open for research. Secondly, such culinary claims, which we have termed “Kitchen stories”, provide valuable opportunities in education at various levels (see below). Thirdly, interesting questions might be revealed by laypeople, craftsmen (chefs, artisans) or even school children which in turn could end up as relevant research topics to be studied within various sciences. Finally, such kitchen stories are valuable parts of our cultural heritage and provide rich research material for scientific fields such as cultural history and sociology (see figure above).

Ongoing efforts
Thus far, we have seen several efforts toward the study of such culinary claims within food science (molecular gastronomy, MG) and since publication of Curious Cook several publications do mention such claims as part of the programme of molecular gastronomy (This, 2009; Vega & Ubbink, 2008). [1] Examples of scientific studies on culinary claims are research on beef stock cooking from the University of Copenhagen (Snitkjær et al., 2010; Snitkjær et al., 2011) and INRA Paris (This et al., 2004). Another example is whether it is a good idea (for the flavour of the dish) to separate the peel and seeds from the flesh before using tomatoes (Oruna-Concha et al., 2007). Even though some such claims have been studied within MG/food science we are not aware of studies starting from such claims within other disciplines such as ethnology, food history, sociology etc. [2] Following up one of the examples above, one might thus ask

• What claims about making beef stock do we find around the world?
• Are the various versions of one claim similar or qualitatively different?
• Do they exist in some countries/areas, being absent in others? How are they distributed geographically and in time?
• etc.

Since producing, cooking and eating/enjoying food is among the most influential phenomena throughout human history such claims should be relevant and important questions to research. Furthermore, a large proportion of such knowledge is rooted in tradition and we are thus in a hurry to collect/record it because much of it lies in the hands and minds of people only. We should not trust that our modern, globalised and urbanised society will hand down this knowledge to the coming generations in like manner as done in past times. Also, examples exist of the potential in using such claims in various levels of education. In France efforts have been carried out in schools, such as “Ateliers expérimentaux du gout” and “Programme “Dictons et plats patrimoniaux””. [3] Also we are underway, through educational research in Finland (Västinsalo & Aksela, 2011) and Norway (Fooladi, 2010), to unveil what potential this might have in science and home economics education. A collection of possible research topics/questions is given in the appendix (link to Fooducation). Our opinion is that this should be a dynamic and expanding list, adding new questions and perspectives along the way.

Prospects and invitation
We believe that this project might involve, perhaps even integrate, a manifold of disciplines as well as various research methodologies/paradigms. As shown in the figure, the phenomenon “culinary claims” forms the centrepiece, allowing the various disciplines to maintain their distinctive features, but also to let them meet in a common point of interest. Our goal is to build an international collection of kitchen stories and culinary claims to be developed and benefitted by researchers of different fields (a French collection exists [4]). We would also like to build a network for researchers, teachers, schools, practitioners and others with a common interest in this topic. Currently no funds are available, but several national applications are in. If you are interested in joining this network, let us know. At this point, we have not set any limits to who might join in, regardless of profession. Further, if you are aware of similar type of efforts, we’d be happy to learn about them.

Contact (in alphabetical order)
Anu Hopia, University of Turku, Functional Foods Forum. Professor (food development). E-mail: anu.hopia (a t) utu.fi. Web page (in Finnish): http://molekyyligastronomia.fi

Erik Fooladi, Volda University College, Norway. Associate professor (chemistry, home economics, teacher education). E-mail: ef (a t) hivolda.no. Web page: http://fooducation.org

Jenni Vartiainen, Helsinki University, Finland. Coordinator of Finland’s science education centre LUMA, PhD student. E-mail: jenni.vastinsalo (a t) helsinki.fi. Web page: www.helsinki.fi/luma/english

Dr Maija Aksela (professor), head of Finland’s Science Education Centre and the Unit of Chemistry Teacher Education, University of Helsinki. E-mail: maija.aksela (a t) helsinki.fi

Notes
[1] Some collections are available on the web, e.g. http://kitchen-myths.com and they appear to be tool to raise interest of public to natural sciences. However, many such efforts often have a rather one-sided perspective in which science carries “the truth” which is used to “debunk the fallacies of tradition”. We believe in a meeting ground for both science and tradition where both can contribute to the other on more equal terms.
[2] We do not, however, claim that such research does not exist, and would be delighted to see such research.
[3] We are not aware of whether these efforts have been followed by educational research.
[4] www.inra.fr/la_science_et_vous/apprendre_experimenter/gastronomie_moleculaire/une_banque_de_precisions_culinaires

References
Fooladi, E. (2010). “Kitchen stories” – Assertions about food and cooking as a framework for teaching argumentation. Paper presented at the XIV IOSTE Symposium, Bled, Slovenia. http://www.ioste14.org/publications/

McGee, H. (1990). The Curious Cook – Taking the lid off kitchen facts and fallacies. San Francisco: North Point Press.

Oruna-Concha, M. J., Methven, L., Blumenthal, H., Young, C., & Mottram, D. S. (2007). Differences in Glutamic Acid and 5′-ribonucleotide Contents Between Flesh and Pulp of Tomatoes and the Relationship with Umami Taste. Journal of Agricultural and Food Chemistry, 55(14), 5776-5780. doi: 10.1021/jf070791p

Snitkjær, P., Frøst, M. B., Skibsted, L. H., & Risbo, J. (2010). Flavour development during beef stock reduction. Food Chemistry, 122(3), 645-655. doi: 10.1016/j.foodchem.2010.03.025

Snitkjær, P., Risbo, J., Skibsted, L. H., Ebeler, S., Heymann, H., Harmon, K., & Frøst, M. B. (2011). Beef stock reduction with red wine – Effects of preparation method and wine characteristics. Food Chemistry, 126(1), 183-196. doi: 10.1016/j.foodchem.2010.10.096

This, H. (2009). Molecular Gastronomy, a Scientific Look at Cooking. Accounts of Chemical Research, 42(5), 575-583. doi: 10.1021/ar8002078

This, H., Meric, R., & Cazor, A. (2004). Lavoisier and Meat Stock. Comptes Rendus Chimie, 9, 1510-1515. doi: 10.1016/j.crci.2006.07.002

Vega, C., & Ubbink, J. (2008). Molecular Gastronomy: A Food Fad or Science Supporting Innovative Cuisine? Trends in Food Science & Technology, 19(7), 372-382. doi: 10.1016/j.tifs.2008.01.006

Västinsalo, J., & Aksela, M. (2011). Using kitchen stories as starting point for chemical education in high school. Paper presented at the ESERA 2011, Lyon, France. http://www.esera2011.fr/en/scientific-programme.html

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

A book I’ve been looking forward to for a long time is The Kitchen as Laboratory: Reflections on the Science of Food and Cooking. It is now available for pre-order with expected delivery on January 31st, 2012. Work on the book began back in 2008, and that year coincidentally marked the 20th anniversary of But the crackling is superb, a refreshing anthology on the science of cooking and eating edited by Nicholas and Giana Kurti. The editors of The Kitchen as Laboratory, Cesar Vega Morales, Job Ubbink and Erik van van der Linden, wanted to continue in the spirit of this book. Through 35 essays the invited chefs, scientists and cooks explore topics of their choice, often based on experiments in their own kitchen. This includes a contribution by me on the Maillard reaction and how we – often without thinking about it – increase it’s rate in different ways when cooking. As for the other contributions, based on the preliminary lists all I can say is that I look forward to read the book!

The book Cooking science – Condensed matter by Adria Vicenc came out last year, but only recently did it appear on my radar. This 75 page preview suggests that it is part coffee table book and part documentation of modern Catalan cuisine combined with short essays on various topics such as food preservation and synaesthetic cooking. Add to that a dash of technology and large photos and descriptions of a sous vide water bath, a rotary evaporator, a freeze drier etc. It’s kind of like a light version of Modernist Cuisine. In his introduction Ferran Adria states that: “As has happened throughout history in the majority of the stages of human evolution, the new technologies act as a support for the progress of cookery”. This is technology with a purpose: better food!

More information in Catalan, Spanish and English is available from the Materia Condensa website. The book features QR codes which lead to various digital resources (also available directly from the website).

The book features a periodic table of preserves (full resolution view available through this preview) which I’ve now added to my list of other food related periodic tables. Fun? Yes! Useful? Probably not…

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).

For a book about food this is a rather unusual book. The author states in the preface that the goal of the book is to “point out new ways of thinking about the tools” that are found in the kitchen. It’s not a book you’ll pick up for its recipes, even though the 100+ recipes included are fine. And it’s not a book you would pick up because of mouthwatering photographs of food. It is however a book that could trigger a lifelong interest in cooking among those who are scientifically minded. Where an experienced chef can read between the lines of a recipe, the rest of us can turn to books like Cooking for geeks to get hints on how to turn a recipe into a tasty dish.

The book is filled with advice ranging from the obvious (when straining pasta, pour the boiling water away from you) to the interesting and brilliant, such as the best way of cracking an egg. My experience from working in a shared lab is that you can learn a lot from observing how your colleagues work in the lab. A kitchen is not too different from a lab, and Potter has done a good job capturing small, trivial and “obvious” details, the tricks of the trade. For an inexperienced cook the obvious is often the best place to start, and it’s a good thing the author dares to include this kind of advice.

Following tips on kitchen tools and gadgets, how to pick a recipe, how to organize the kitchen and how to calibrate equipment, the book focuses on the basics of flavor. But where many science books leave it with descriptive text about taste and smell, Potter goes on to propose experiments to try out in the kitchen. And the systematic and analytical mind of the authors shines through when he lists typical bitter, salty, sour, sweet, umami and hot ingredients from different regional cuisines.

The chapter which may have the greatest potential of improving your cooking, covers time, temperature and cooking methods. Depending on the meat used the denaturation of proteins occurs at different temperatures. That’s why it’s important to know at which temperature you cook. Combine this with different methods of heat transfer (conduction, convection, radiation) and varying rates of heat transfer in foods, and you’re left with a complex set of equations to solve in order to obtain a steak with a nicely browned surface, an outer layer which is not overcooked and a core with the desired doneness. Luckily there are easy ways to achieve this, and the book includes an introduction to sous vide cooking and the hardware needed for this. Using temperature controlled water baths (not unlike the ones used in chemistry labs), meat is sealed in plastic bags and cooked at the desired core temperature, thereby avoiding heat gradients all together. For better flavor, a quick browning is recommended to get the Maillard reaction going.

The chapter “Playing with chemicals” may frighten the average consumer, but certainly warms the heart of chemist who is well aware of the many pure chemicals and polymers found in the kitchen. Sugar, salt, acids and bases are well known, hydrocolloids perhaps less so. But they are even more fun to play around with. Ranging from well known starch and gelatin to more exotic gelling agents such as agar, carrageenan and sodium alginate to mention a few, Potter explains the science and gives practical tips on how to succeed with the recipes.

In between the many fact boxes, recipes and tables there are also more than 20 interviews with scientists, food professionals, and bloggers to be found. Again, not very common for a cook book, but it fits in nicely with all the other bits of information. At this point I should also mention (in the interest of full disclosure) that as a food blogger I was one of the lucky persons to be interviewed for the book.

Jeff working on an ice cream maker made with Legos. (Photo © 2009 Atof Inc.)

Jeff Potter is a computer scientist and makes no attempt at hiding this in the book, for instance when he wants to overclock an oven to make a perfect pizza. The book is strewn with “hacker lingo”, and what some may term a good sense of humor others frown at as geeky jokes and unnecessary references to software engineering. In my opinion the book could have reached an even greater audience without the references to computer science. Apart from this my main objection against the book is the lack of color photos, and the minuscule size of the b/w photos. Some of the pictures are available in color and high resolution through flickr.com though, and the author also encourages users to post pictures tagged with “cookingforgeeks” at the same site.

Despite these objections it is a well researched book, and the wide range of topics and the number of fun facts, hacks and tips is amazing. Jeff Potter succeeds in bringing popular food science to a broad audience, and I’m convinced that the book could even find its place in science education and as a source of inspiration for science projects. The book also encourages a work methodology that is familiar to every chemists: experiment and observation. This is obvious in the lab, but just as useful in the kitchen. And in case you’re still curious about the eggs: Crack them on a flat surface. This will result in larger pieces that aren’t pushed into the egg. Since I read this tip I’ve tried it several times, and it works very well!

Review by Martin Lersch
Based in Norway, organic chemist Martin Lersch blogs about food and chemistry at Khymos (blog.khymos.org) besides his day time work in R&D at a biorefinery.

Copyright Nature Chemistry. This review was first published in Nature Chemistry as “Kitchen hacks for better cooking” (Lersch, M. Nature Chemistry 2010, 1001. DOI: 10.1038/nchem.879).

Cooking for Geeks
by Jeff Potter
O’REILLY MEDIA: 2010.
432 pp. $34.99

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