Posts Tagged ‘tools’

A mathematician cooks sous vide

Sunday, January 18th, 2009

douglasbaldwin
Douglas Baldwin with two immersion circulators and a vacuum chamber sealer.

Since I got my immersion circulator in December I’ve discovered that there are two critical questions that always come up as I hold a piece of meat in my hands, ready to cook it sous vide: At what temperature should I cook this? And for how long? Despite the fact that two books were published on sous vide last fall it is the short yet comprehensive guide “A Practical Guide to Sous Vide Cooking” by Douglas Baldwin that I’ve found most useful to answer these questions. Those who have followed the eGullet thread on sous vide cooking will probably recognize Douglas Baldwin as one of the major contributors alongside Nathan Myhrvold. Out of curiosity and eager to learn more I therefore emailed Douglas and asked if he would be interested in doing an email interview.

ML: From your homepage I see that you are a PhD student in applied mathematics, how did you become interested in sous vide?

DB: I have always loved to cook. Before last January, though, I mainly cooked slow food. That is when I saw sous vide mentioned in one of Harold McGee’s NY Times articles. Wow. Cooking meat at its desired final core temperature is so obvious! As a mathematician, I kicked myself for never asking “if overcooked meat is bad, what temperature should the meat be cooked at?” A question which many mathematician would instantly answer, “just above the temperature you want it to end up at.”
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Santa came early this year!

Friday, December 12th, 2008


An brown box arrived today!
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Ten tips for practical molecular gastronomy, part 9

Saturday, May 31st, 2008

9. Keep a written record of what you do!

Wouldn’t it be a pity if you couldn’t recreate that perfect concoction you made last week, simply because you forgot how you did it? Last year I made a vegetable soup to which I added garam masala and pepper. I was cooking ad lib, adding a little of this and that without taking notes… Which is annoying, because it turned out very nice! It had a remarkable aftertaste which gave me a somewhat dry feeling on the back of the tongue and it reminded me of mangoes. Even immediately after the meal I wasn’t able to recall all the ingredients.

As an undergraduate student I took an organic chemistry lab course, and I remember we were told not to use post it notes or small pieces of paper for taking notes. Everything should be recorded in a proper journal or – if necessary – small note books. Having finished my Ph.D. a couple of years later, I can only testify to this. Everything you do – be it in the lab or in the kitchen – should be recorded immediately in a journal. It’s amazing how something that was obvious one day, slips your mind a week or month later.

There is a wonderful Donald Duck story by Volker Reiche entitled “The soul of science” (the original appeared in 1981 in the Dutch Donald Duck magazine). At a point “Professor Duck”, who actually works as a janitor in a lab, utters the words “Careful notes are the soul of science” as he is caught experimenting. This is true also for the kitchen and experimental cooking. A German translation of the story was reprinted in the article “Das Leiden des cand. chem. Donald Duck” (open access) in case you want to read the whole story.


Careful notes are also the soul of kitchen science!

When taking notes it’s essential that you are able to re-cook the dish yourself. But if no one else is, the notes are of limited value. The biggest source of uncertainty in the kitchen is the widespread use of volume for measuring powders. This can best be illustrated by the question: How much does a cup of flour weigh?

I bumped into this when I began baking no-knead bread (recipe). I converted the recipe to metric units using an online calculator, but the no-knead bread wasn’t a huge success. The problem was that there is no simple answer to the question “How much does a cup of flour weigh?”. Cooking conversion online states that a cup of all-purpose flour weighs 99 g. King Arthur Mills claim that all their flours weigh 113 g/cup. USDA states 125 g/cup and Gold Medal 130 g/cup. Some cookbooks have settled at 140 g/cup (apparently because this is about half way between a loosely and densly packed cup) and if the flour is hard packed you can reach 160 g/cup. In other words – when following a recipe you would need to know how the volume of flour was measured in order to use exactly the same amount of flour. Some recipes call for “spoon and level” or “scoop and level”, but many do not include any information about this.

My recommendation is to weigh all dry ingredients (and preferably also the wet ingredients). A normal digital kitchen scale typically has a resolution of 1 g with an accuracy of +/- 5 g and they are quite affordable. Weighing liquids is also far more accurate than the average volume measurement in the kitchen. If the scale has a “tara” function it’s also much faster as you can zero the display after each ingredient you add. It shouldn’t come as a surprise that I’m not the only chemist advocating weight measurements in kitchen. And it’s not difficult finding other sites in favor of weight measurements either.

It therefore puzzles me why recipes that call for the following are still so abundant:

1 pack of instant yeast
1 envelope unflavored gelatin
1 gelatin sheet (see comment #4-5)
1 sachet powdered pectin
1 tablespoon liquid pectin
1 stick of butter
… and the list goes on

The only exception to the general advice on weighing ingredients is when very small quantities are used. This could be spices, food coloring or hydrocolloids. With normal kitchen scales, you’ll be better of using volume measurements for amounts less than 5 g (equal to a teaspoon if measuring water). Otherweise it’s worthwhile mentioning that scales with a 0.1 g and 0.01 g readout are getting cheaper and cheaper.

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There is a summary of the “10 tips for practical molecular gastronomy” posts. The collection of books (favorite, molecular gastronomy, aroma/taste, reference/technique, food chemistry) and links (people/chefs/blogs, webresources, institutions, articles and audio/video) at khymos.org might also be of interest.

Kitchen gadgets

Thursday, October 11th, 2007

Popular science magazine has an amusing article on “The future of food” which portrays Dave Arnold, apparently the “man behind the curtain of today’s hottest movement in cooking”. I don’t buy all of this, but he’s no doubt had a central role in bringing lab equipment into the kitchens of North American chefs and teaching them a little science. You might also want to check out their gallery of kitchen gadgets. Some of my favorites include (click the pictures to lanuch the picture gallery at PopSci magazine):

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For the Pros: The Whipper. Adds a touch of air to every bite.

Within reach of the dedicated amateur chef, indispensible for the professional chef: a whipper which you can charge with either carbon dioxide (for instance to make carbonated fruit) or dinitrogen oxide (too make foams/espumas or simply whipped cream).

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For the Pros: The Sealer and Circulator. Cooks in a bag to lock in juiciness.

Sous vide cooking is perhaps one of the most fascinating examples of science inspired cooking. The picture shows a vacuum sealer and a thermostated water bath circulator. If this is too expensive, check out my post on a simple and easy DIY sous vide.

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For the Pros: The New Spice Rack. Chemicals the experimental home chef shouldn’t be without.

Last but not least: the different chemicals which become more and more available. I’ve put together a collection of hydrocolloid recipes which will help you get started using these fascinating chemicals. If you have troubles getting hold of these, my list of suppliers might help you.

Of course I’d like to put my hands on a Pacojet, an Antigriddle or a Gastrovac as well, but for a home kitchen, this gets too exotic and far too expensive. But – the most surprising gadget was the vacuum meat tumbler from Reveo. Just like the extremely expensive Gastrovac, this little machine can be used for vacuum impregnation of meat and other foods (or at least this is something I assume from the description). IMHO vacuum impregnation is the most important feature of the Gastrovac – far more important than the heating capabilities. Perhaps someone owning a Reveo could report back?

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For the Home: Meat, Your Maker. This vacuum tumbler cuts marinating time by hours, first extracting air to expand the meat’s fibers and then spinning it so that every area is exposed to your sauce of choice. Probably doesn’t beat a good long soak, but perfect for when barbecue inspiration suddenly strikes.—Abby Seiff

But I was very dissapointed that my all-time favorite kitchen gadget didn’t make it into the gallery: a simple thermometer. As I have stated in one of my tips for practical molecular gastronomy, this is probably the single tool that can improve your cooking the most.

Clarification of stock and other liquids

Monday, September 3rd, 2007

In a comment to the last post, Chad asked how the clarification with laboratory glass ware works. Here’s how. Basically it’s a filtration. But if you would use a normal filter paper (such as a coffee filter) and let gravity pull the liquid through the filter, it would take ages. By applying a vacuum to the back side of the filter, the stock is sucked through (or pushed if you like by the atmospheric pressure). The are several possible sources of vacuum. The simplest and cheapest is a water aspirator or a handpump. More expensive solutions include a membrane pump or an oil pump. The particles you want to remove are from 0.0001 mm and upwards to > 1 mm. The best thing would be to first pass the stock through a cheese cloth or a muslin, followed by one or more filtrations using filter paper. This would gradually yield a perfectly clear solution. Pictures of a Büchner funnel, Erlenmeyer flask and a water aspirator can be found on the tools page of Khymos. Pictures of a complete setup can be found by googling. If doing this in a kitchen, you would want to have an Erlenmeyer flask of at least 2-3 L as this is where the clearified stock is collected. The Büchner funnel should preferably have a diameter of 12 cm or more.

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The fascinating thing about a filtration like this is that you can also remove color. At the EuroFoodChem XIV conference I was told by Jorge Ruiz of Lamaragaritaseagita that you can make perfectly clear tomato juice by succesive filtrations, starting with a coarse filter and moving to finer filters. All in all, 3-5 filtrations should be sufficient.

Carbonated fruit the iSi way

Monday, April 9th, 2007

I blogged about carbonated strawberries some while ago. Those were made using dry ice which unfortunately is not always easy to get hold of. Last week however I bought a iSi Gourmet Whipper – one of those Ferran Adria uses to make foams/espumas. I plan to experiment with that as well, but the first thing I decided to prepare was carbonated fruit. In fact this is a safe way (the only?) to make carbonated fruit at home using a pressurized container.

isi-whipper.jpg

The instruction booklet which comes with the iSi Gourmet Whipper only mentions cream chargers (filled with N2O, dinitrogen oxide), whereas soda chargers (filled with CO2, carbon dioxide) are not mentioned (I guess the opposite is true for the iSi Siphons?). This is quite amazing actually! Luckily however the cream and soda chargers are exactly the same size and both hold 8 g of gas. So it should be possible to make carbonated fruit with any of the iSi whippers (cream, easy, gourmet, dessert, thermo) or siphons available.

Here’s how you proceed:

  1. Fill you iSi whipper (or siphon) with fruit, preferably fruit which has a cut, wet surface to allow the carbon dioxide to dissolve in the water/juice.
  2. Screw on top securly
  3. Charge with one soda charger (two if you have the 1 L whipper)
  4. Leave in fridge over night
  5. Release pressure with valve (Important!)
  6. Unscrew top and serve immediately!
  7. Enjoy!

carbonated-grapes.jpg
This is what carbonated grapes look like. As you see, I decided to cut the grapes in to halves.

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Notice how they sizzle!

A quick recap of the chemistry: cold water dissolves more CO2 than tempered water, that’s why we leave it in the fridge. Also, remember that it takes some time for the carbon dioxide to dissolve in water, therefore it’s better not to be in a hurry. A quick calculation of the pressures gives the following: Both gases have molecular weights of 44 g/mol, so 8 g of gas corresponds to 0.1818 moles or 4.1 L at 25 °C and 1 atm pressure. The volume of the chargers is 0.01 L which gives an initial pressure in the chargers of impressive 445 atm! With an approximate volume of 0.7 L this gives a pressure (in an empty whipper) of nearly 6 atm – the same as in a bottle of champagne. However once you add water, the equilibriums will change and the pressure in the head space will drop. Anyone who remembers how to calculate the head space pressure at equilibrium if the container is filled with 0.5 L of water and cooled to 4 °C?

I’ve done some googling and there is also some mention of making carbonated fruit with an iSi whipper over at Ideas in food.

(The word play in the title works better for those with a mother tongue where iSi would be pronounced just like “easy”!)

First experiments with sodium alginate

Friday, March 30th, 2007

Here’s some pictures and a video of my first experiments with sodium alginate and spherification. I used sodium alginate from the Texturas series and calcium chloride from a drug store. Needless to say, I’m very fascinated by the texture and the whole process. I have blogged about the chemistry behind previously.

Materials used:
2.0 g sodium alginate
200 g water (with low calcium content!)
50 g blueberry syrup

2.5 g calcium chloride
500 g water

Procedure:
2 g sodium alginate and 200 g water were mixed vigourously in blender. The mixture was then left to stand for some hours to get rid of the air bubbles. 50 g blueberry syrup was then added to the sodium alginate solution. A calcium chloride bath was prepared by dissolving 2.5 g calcium chloride in 500 g water. The sodium alginate/blueberry mixture was dripped into the calcium chloride bath using a plastic syringe with a steel cannula. After 1-3 min the pearls were removed and rinsed with water.

More detailed procedure with pictures and video:
I had to obtain a scale with a 0.1 g accuracy to weigh out 2.0 g of sodium alginate (my first experiments using a normal kitchen scale failed). The model I got cost about $100 and is inteded for school laboratories. Amazon provides several scales with this accuracy.

alginate-1.jpg

I used a blender to dissolve sodium alginate in water. This incorporates a lot of air in the mixture which we don’t want. It could possibly be avoided by using an immersion blender/mixer. However, I just left the alginate solution on the bench and after 3-4 hours the air bubbles had all escaped from the solution.

alginate-2.jpg

Plastic syringes and cannulas can be obtained from your local drug store or pharmacist. I found it was easier to produce evenly sized drops with a sharp cannula (CAREFULL!) than with just the plastic tip of the syringe. This of course depends on the viscosity of the solution. By thickening (with xanthan for instance) you can produce larger drops.

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After 1-3 min the spheres were removed from the calcium chloride solution and rinsed with clean water. I dried the spheres carefully using a kitchen towel or paper.

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Definitely looks like caviar when presented on a spoon like this!

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Larger spheres were made by filling a small measuring spoon with the alginate mixture (I used a syringe for this so the outsides of the spoon would not be covered with alginate solution) and carefully emptied it into the calcium chloride bath. It takes some trial and error to achieve good results.

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The spheres are suprisingly robust and can be handled without rupturing.

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If cut with a knife, the spheres rupture and the liquid contents flows out.

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The small spheres didn’t taste much, so I could have added more blueberry syrup. The large spheres however had a nice taste. The surprise element when they rupture in your mouth is very nice!

Staying warm: Cast iron vs. stainless steel

Thursday, March 1st, 2007

Cookware made from cast iron has a reputation for keeping food warm for a long time. Is that really true? Best way to find out is by an experiment. I decided to compare a cast iron pot with one of stainless steel. These are the pots I used:

cast-iron-stainless-steel.jpg

For the first experiment I filled them each with 2,5 L of water, put the lids on and brought both to the boil and let them boil for a minute so the pot itself would be warm throughout. Then both were placed on cork plates and left to cool. The temperature probe was carefully inserted under the lid in order to reduce the heat loss, and removed once the temperature had stabilized. For the second experiment 5 L of water were used. The measured temperatures are shown in the graph.

cooling-curve.jpg

Contrary to what I had expected, the stainless steel pot keeps water warmer! After approximately 1,5 hours there is a 10 °C difference between the two. As expected, when using 5 L of water, it stays warm longer. Physical data for the two pots are given in the following table:

Cast iron Stainless steel
Volume 6 L 6 L
Diameter 27,9 cm 25,0 cm
Height 11,5 cm 14,5 cm
Surface area
(top+sides)
1619 cm2 1629 cm2
Surface area
in contact with 5 L water
1301 cm2 1286 cm2
Weight 6,1 kg 2,3 kg
Wall thickness ~4 mm <1 mm
Heat capacity of pan 2,8 kJ/K 1,2 kJ/K
Thermal conductivity 80 Wm-1K-1 16 Wm-1K-1
Thermal diffusivity 22 x 10-6 m2/s 4.3 x 10-6 m2/s
Emissivity 0.95 0.07

The heat capacity of the cast iron pot is more than double that of the stainless steel pot. But this is negligible compared to the heat capacity of water: 10.5 kJ/K (2,5 L) and 20,9 kJ/K (5,0 L). Also, there is only a small difference in their surface area which cannot explain the large difference in temperature loss observed.

This leaves me with two eplanations:

  • Cast iron is better heat conductor and has a higer thermal diffusivity
  • Cast iron (being nearly black) has a much higher emissivity than a polished stainless steel surface. The reason for this is that absorption and reflection of radiation are related.
  • My guess is that the difference in emissivity is more important (but please correct me if I’m wrong). With an infrared thermometer, one should therefore be able to measure a difference between pots of cast iron and polished stainless steel (even though they’re at the same temperature!) due to the difference in emissivity. Any one who can do the experiment and report back?

    Conclusion: There are many good reasons to use cast iron, but keeping food warm is not one of them!

    Ten tips for practial molecular gastronomy, part 2

    Sunday, February 11th, 2007

    2. Know what temperature you’re cooking at.

    A dip probe thermometer with a digital read out is a cheap way to bring science into your kitchen. It should preferably cover the temperatures from -30 to 300 °C (-22 to 570 °F). It’s a good idea to check how accurate it is. This is easily done using a water/ice mixture and boiling water.

    calibrate-zero.jpg

    Fill a glas with crushed icecubes and top of with cold tap water. Leave if for some minutes for the water to cool and stir every now and then. Make sure the tip of the probe does not come in direct contact with ice. A mixture of water and ice is exactly 0 °C (32 °F). If the reading is off by 2 °C (~4 °F) or more I would take the thermometer back to the shop and claim a refund.

    calibrate-ninetynine.jpg

    Similarly, you can use boiling water as a high temperature reference point. Water boils at 100 °C (212 °F) at sea level and standard barometric pressure. The exact boiling point at your location can be calculated.

    When I bought my first thermometer it turned out that the temperature readings were quite erratic so I had to return it. The one I have now however works fine (1 degree off for the boiling water is OK).

    As an addition to a dip probe thermometer, contact-less thermometers with infrared sensors are becomming more affordable. Suppliers include Raytek, Strathwood, Radiant (here, here or here) and Extech Instruments (links to product pages at Amazon).

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

    Ten tips for practical molecular gastronomy

    Saturday, January 27th, 2007

    In a recent survey 72% of chefs say they may want to experiment with molecular gastronomy in 2007. That’s an impressive number and considering the attention molecular gastronomy gets in media I bet many home cooks would want to experiment in the kitchen as well. Here’s a list of things to consider if you want to make a scientific approach towards cooking:

    1. Use good and fresh raw materials of the best quality available.

    2. Know what temperature you’re cooking at. A dip probe thermometer with a digital read out is a cheap way to bring science into your kitchen.

    3. Get a basic understanding of heat transfer, heat capacity and heat conductance. “Heat” in this context des not imply high temperature since it also applies to the understanding of freezing/thawing.

    4. Learn how to control the texture of food. Some key points: temperature induced changes (freezing, heating), emulsifiers, thickeners, gelling agents, moisture content, pressure/vacuum, osmosis.

    5. Learn how to control taste and flavor. Some key points: flavor pairings, spice synergies/antagonies, influence of temperature (Maillard reaction, caramelization, temperature stability, volatility), taste enhancers, taste suppresants, solubility of flavour compounds in fat/water, extraction.

    6. Remember that prolonged exposure to a flavor causes desenzitation, meaning that your brain thinks the food smells less even though it’s still present in the same amount. Therefore, let different flavours enhance each other. Similarly, variation in taste, texture, temperature and color can open up new dimensions in a dish. This is referred to as “increased sensing by contrast amplification”.

    7. Be critial to recipes and question authority – they do not necessarily represent “the truth”. Nevertheless, you can certainly learn a lot from the experts.

    8. Dare to experiment and try new ingredients and procedures. Do control experiments so you can compare results. When evaluating the outcome, be aware that your own opinions will be biased. Have a friend help you perform a blind test, or even better a triangle test to evaluate the outcome of your experiments.

    9. Keep a written record of what you do! It would be a pity if you couldn’t recreate that perfect concoction you made last week, simply because you forgot how you did it.

    10. Have fun!

    blue_gas_flame.jpg
    Heat causes many changes in food, but few appreciate how important it is to know at what temperature they are cooking and at what temperature the desired change occurs.

    These tips for molecular gastronomy relate to the technical and scientific aspects of food preparation and eating, and I plan to elaborate on each of the points in separate blog posts. However, according to Hervé This’ definition of molecular gastronomy, one should also investigate the social and artistic components of cooking. A good example of this is the “Five Aspects Meal Model” developed at Grythyttan in Sweden (Gustafsson, I.B. et al. Journal of Food Service, 2006, 84.). Although intended for a restaurant setting, the general idea can also be applied for home cooking.

    The meal takes place in a room (room), where the consumer meets waiters and other consumers (meeting), and where dishes and drinks (products) are served. Backstage there are several rules, laws and economic and management resources (management control system) that are needed to make the meal possible and make the experience an entirety as a meal (entirety – expressing an atmosphere).

    Or to put it differently: average food eaten together with good friends while you’re sitting on a terrace with the sun setting in the ocean will taste superior to excellent food served on plastic plates and eaten alone in a room with mess all over the place.

    One last thing: once you’re finished in the kitchen with your culinary alchemy, your gastro physics, your cutting edge science cuisine, your molecular cooking, your hypermodern emotional cooking, your science food or whatever fancy name you attach to it – remember the social and artistic components when you serve the food. Just so people won’t refer to you as a techno chef, a mad scientist or a modern day Willy Wonka. After all, molecular gastronomy is about the science of deliciousness, not technical wizardry.

    Questions and topics for future blog posts are welcome at webmaster [a] khymos.org (substitute @ for [a]) or as a comment below.