The 6X °C egg, or "opposite-boiled eggs" revisited

Some years ago I experimented and wrote about what happens if you cook an egg not in boiling water but at, say, 64 °C. I met upon some surprising results ("The opposite boiled egg"), but could not give good reasons for why. But now, at last, the answer to why has appeared in the scientific literature!

According to Harold McGee the "[...] egg white begins to thicken at 63 °C and becomes a tender solid when it reaches 65 degrees". Furthermore, "The yolk proteins begin to thicken at 65 °C and set at 70 °C [...]". (McGee, pp. 85) The molecular gastronomer Hervé This also writes about this in a similar manner in e.g. "Molecular gastronomy - Exploring the Science of Flavor".

So, for the perfect egg, keep it in a water bath at 65 °C for a long time, and you get an egg with a solid white and soft yolk. I tried cooking times between 1 and 26 hours, and at various temperatures, mostly between 62 and 68 °C.

This is of course inspired by methods used for meat where you can keep the temperature at, say, 58 °C and the meat will stay red still after a day in the water bath (low temperature and sous vide methods). It's not unnatural to think that the same applies to eggs, since both meat and eggs are mostly proteins and water.

The picture to the right shows 68 °C egg creation by Finnish chef Arto Rastas, taken from Anu Hopia's blog molekyyligastronomia. See the bottom for recipe/procedure.

The surprising result

In my experiments the eggs at 62-65 °C turned out "opposite boiled": a solidified (but not entirely solid) yolk came rolling out through a runny white! And on top of it, the time did seem to make a difference. Were my experiments poorly conducted, or was the suggested theory wrong?

December issue of school science magazine on food

The last issue of the Norwegian science education magazine "Naturfag" (equivalent to "School science") has several articles on food previously posted here on fooducation. The magazine is in Norwegian and free for download.

Issue 2/2009 with mostly Christmas- and winter related content includes the following articles based on fooducation posts. Most of them are updated/revised versions and are also found as updated versions on the Norwegian Centre for Science Education "gastronomic school science" web pages www.naturfag.no/mat (Google translation here):

1. "Christmas dinner trimmings - a hot potato?" (part 1 and part 2) and "Green vegetables and chlorophyll revisited" combined
   
   
2. "Deciphering an old preserves recipe"
   
   
3. The effect of added sugar, salt and high temperature on microorganisms/yeast. This is not previously published on fooducation, but a time lapse video with captions in Norwegian can be seen on YouTube. It is self-explanatory, i guess. The purpose is to show an easy to set up experiment for testing conditions under which microorganisms thrive or die. Relevance is to baking (you want to promote the yeast) and preservation (you want to suppress or kill microorganisms)
   
   
4. "Leavens in cookies - theory and practice"

The latter also made it into the news section of "Nysgjerrigper", a science knowledge project from the Norwegian Research Council.

Of course there are several other interesting topics in the issue as well, such as "Gingerbread house architecture" "Catch sight of and predict the northern light" and more.

Merry Christmas

Egg cooking calculator

As this year's Easter greeting, Deptartment of Chemistry at the University of Oslo has developed an egg cooking calculator with reference to Martin's Khymos and my Maturfag ("Norwegian fooducation").

The issue of cooking the perfectly boiled egg has been discussed several places, amongst others on Khymos, fooducation, and on "Maturfag" which is fooducation's teacher resource pages at the Norwegian Centre for Science Education (Google translation of the resource pages here). Also, Douglas Baldwin's Practical guide to sous vide cooking has an excellent section on controlled-temperature cooking of eggs.

Formula for calculating the boiling time for eggs. For details and
references, see Khymos egg boiling post

Now, Department of Chemistry in Oslo has converted this formula into an interactive animation/calculator for cooking your Easter egg the way most people do it: in boiling water. This has already collected some attention, amongst others in the national newspaper VG (and supposedly on radio at the national broadcasting corporation NRK during Easter holiday). The cooking time depends on several factors, taken that you use boiling water:

• egg size (circumference around the thick end)
  
• initial temperature of the egg
• altitude (since temperature of boiling water varies according to this)
  
• the way you like your egg (soft, hard, medium)
  

The categories should be rather self-explaining. Click the illustration to go to the calculator
(I love the nifty automatic timer function :)

Tip: For measuring the circumference of the egg, use a piece of string and measure the length that goes around the "belly" of the egg.

Happy Easter holidays

A great loss

Not long ago, I was told that the Swedish physicist Hans-Uno Bengtsson regrettably had passed away. A great loss for many of us that appreciated his unique way of illuminating the science in everyday life, and, to me, the physics in food and drink.

Hans-Uno Bengtsson was associate professor at the Department of Theoretical Physics at Lund University, Sweden. According to Wikipedia, Lund University web pages and people I've talked to, he was also an outstanding lecturer. My experience with his work is his writings on the physics of food and drink, although he published a host of other texts on physics, both scientific and popular. To Scandinavian readers, I'd recommend the two books any time

- "Koka soppa på fysik" ("Cooking soup on physics"[?]), a collaboration with the chef Jan Boris-Möller.
A collection of short texts on various food subjects, connecting apparently unrelated subects in an elegant and subtle way

- "Kring flaskor og fysik" ("On bottles and physics"), together with sommelier Mischa Billing.
A conversation between the two authors leading the reader through a meal, discussing various likely and unlikely subjects on the way.

My fascination about these two books is his special ability to interweave complicated physical subjects into the food and drink in a way that makes me gasp from the physics and maths without being put off (i.e. discussing adiabatic expansion in connection with the little "cloud" that arises when a champagne bottle is opened). In fact, in the bottles vs. physics book, he leaves the calculation in the book, but separates it in such a way that the reader very well may skip this part without loosing the thread. Also, the great aesthetic sense that characterises these two books, reveals a great gift both in terms of language/writing and visually.

Finally, I was fortunate enough to experience him a few times on a food programme on TV ("Mat"/"Food" with Tina on Swedish television), amongst others discussing the most efficient way of cooling your champagne: wrap it in a wet towel, strap it on your motorbike and go for a ride :)

I've been hoping for more food- and drink related contributions by Hans-Uno Bengtsson. Unfortunately that won't be, and as I've understood, I'm not the only one that will miss further contributions from Hans-Uno Bengtsson, who left us far too soon.

Erik

"Opposite-boiled eggs" - Cooking an egg with soft white and firm yolk

Cooking an egg we usually use boiling water, and we need to monitor the temperature carefully. One minute too much, and we get a less-than-perfect-boiled egg. Reason: the interior of the egg (aka: the proteins in both white and yolk) coagulates/stiffens at far lower temperatures than 100 °C. According to Harold McGee the "[...]egg white begins to thicken at 63 °C and becomes a tender solid when it reaches 65 degrees". Furthermore, "The yolk proteins begin to thicken at 65 °C and set at 70 °C [...]". (McGee, pp 85)

So, my thought was: Since it's the temperature that counts rather than the time, I can keep the temperature at 64-65 °C, and the egg will be perfect (to my taste) no matter how long they are cooked: a fool proof method to eggs with tender solid white and soft yolk! The pictures show eggs cooked ad 65 and 68 °C for 6 and 26.5 hours, respectively.





Hervé This also writes about this: "[...]at 62 °C one of the proteins in the white (ovotransferrin) is cooked, but the yolk remains liquid because the proteins that coagulate first in this part of the egg require a temperature of 68 °C. Obviously this would mean longer cooking times, but the result is a perfectly cooked egg" (This, pp. 31)

The proof is in the pudding, so I tried cooking an egg at 65 °C exactly for an hour or more, and was to put it mildly surprised. The egg came out with a runny white but firm yolk!! These come out the same whether they're kept for half an hour (to ensure the same temperature throughout the egg) or 26 °C hours. Another proof, provided the temperature is right, for that the time doesn’t matter in coagulating proteins.

There may be several reasons for this, but one is found in McGee (pp 85): "[…]the major [egg white] protein, ovalbumin, doesn't coagulate until about 80 °C".

So, it seems, this time chemistry played me a trick. We will still have to rely on physics: the reason that we can have eggs with firm white and soft yolk is, when using a temperature well above the coagulation temperature, that the white is "overheated" before the temperature of the yolk passes the point where the yolk stiffens.


There is, by the way, a mathematic model/equation for this. Have a look at Martin Lersch's web site on Kitchen chemistry for a nice diagram and explanation of this.


Happy cooking

Erik

References and links:
Harold McGee: On Food and Cooking
Hervé This: Molecular gastronomy - Exploring the science of flavor
Martin Lersch's page "Molecular gastronomy and the science of cooking"

Post-comment (feb. 2009):
Douglas Balwin's excellent "A Practical Guide to Sous Vide Cooking" has a section on sous vide cooking eggs