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All my life, I have pricked a little hole in the blunt end of an egg before boiling it. I was taught the reason is to let the pocket of air inside escape as the insides swell with the heat, to prevent cracking.

WikiHow knows what I am talking about!

Release trapped gas to less the likelihood of cracking. Before you submerge an egg, prick the large end of the shell with a clean thumbtack or safety pin. This will allow the trapped air bubbles—which are normally responsible for cracking—to escape during the boiling process.

Their reference? Our friends over at Seasoned Advice!

A friend looked at me in askance as I prepared eggs in front of her. What? Have I fallen for an old myth? We did a rough-and-ready experiment. I pricked two eggs, and threw in an unpricked control. The result: The exact reverse of my expectation. The two pricked eggs cracked, while the non-pricked one was intact. Now, that's not enough to convince me either way, but it is enough to make me question my belief.

Does pricking a hole in the shell of an egg before boiling it reduce the chance of the egg shell cracking while cooking?

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    +1000 for doing the experiment! – user5341 Mar 17 '17 at 16:05
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    What cracks the shells is the temperature shock. Put eggs in cold water, heat the water and they basically never crack. – Sklivvz Mar 17 '17 at 16:25
  • @Sklivvz Note: That method is good for refrigerated eggs. For room temperature eggs, you would want to start them in room temperature water, for the same reason. – called2voyage Mar 17 '17 at 20:58
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    @Sklivvz: Make that a Skeptics.SE question, so I can debunk it with this 1971 paper! – Oddthinking Mar 17 '17 at 23:33
  • @Oddthinking: "putting eggs into cold rather than boiling water did not reduce the incidence of splitting except when the air space was large, following prolonged storage at room temperature." LIES – Sklivvz Mar 18 '17 at 0:49
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In Germany, it's such a well-known advice to prick eggs before boiling that there is a kitchen tool which exists only to make Eier pieksen easier: the Eierpiekser. My mother had a cheap plastic one (ca. 1970), but it seems that you can pay 10€ or even more for the stainless steel version.

Wikimedia: Eierpiekser (CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=81004)

Yet, not everyone in Germany pricks their eggs before boiling. To quote German science TV show Quarks & Co:

Deutschland ist geteilt – zumindest beim Eierkochen: Zwei Lager stehen sich unversöhnlich gegenüber. Die eine Hälfte pikst die Eier vor dem Kochen an – die andere nicht. ("Germany is divided – at least when it comes to boiling eggs. There are two irreconcilable factions: the half that pricks eggs before boiling, and the other that doesn't.", my translation)

In order to see the truth behind this, they presented in a 2011 episode results from what they claim to be the largest egg-boiling experiment world-wide. They asked viewers to boil eggs and to submit their data to an online database. The data contained information on the cracking status after boiling, whether the eggs were pricked or not, and whether an Eierkocher was used (a kitchen device used exclusively for boiling eggs, which to my surprise exists also outside of breakfast-egg-obsessed central Europe).

The final data set contained data on about 3,000 boiled eggs, roughly half of them pricked, half of them unpricked. As it were, about 12 percent of the unpricked eggs, but only 10 percent of the pricked eggs cracked during boiling. However, the TV show used the opportunity to teach their audience about scientific hypothesis testing, and showed that this difference was statistically insignificant. There was also no interaction with the method of boiling (but I'm not sure if there was a main effect for it).

So, to summarize, after evaluating the series of micro experiments, "Quarks & Co" concluded that it doesn't matter whether you prick eggs before boiling, at least under the conditions of an average German household.

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    Lesson learnt. I shall no longer prick my eggs. – Oddthinking Mar 19 '17 at 1:57
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(I endorse Schmuddi's answer but I'll keep this one for the historical background it provides.)

The advice goes back more than one hundred years to a 20 January 1899 North Dakota Agricultural College, Government Agricultural Experimental Station for North Dakota, Bulletin 35, Some Chemical Problems Investigated by Edwin Fremont Ladd.

However, the advice is for water glass (sodium silicate) preserved eggs, not fresh eggs.

All packed eggs contain a little gas and in boiling such eggs they will crack. This may be prevented by making a pin-hole, in the blunt end of the egg. To do this hold the egg in the hand, place the point of a pin against the shell of the egg at the blunt end and give the pin a quick, sharp blow, just enough to drive the pin through the shell without further injury to the egg.
E. F. Ladd, Agricultural College, North Dakota.

This advice spread rapidly over the next few year, but always specifying that it was for preserved eggs:

See for example:

Irrigation Age April 1899

California Cultivator 20 June 1902 (specifically cites to E. F. Ladd)

The Country Gentleman 5 May 1904 (specifically cites to E. F. Ladd)

Michigan Poultry Breeder May 1904 (citing to the Poultry Herald)

Poultry Herald June 1905 (by Ladd himself)

The Poultry Keeper June 1905

Egg Money, how to Increase it 1908 (cites to E. F. Ladd)

Henley's twentieth century formulas, recipes and processes 1916

US Department of Agriculture 1920

New International Encyclopedia 1930 ("The shells of eggs preserved in water glass are apt to crack in boiling, but, it is stated, this may be prevented by puncturing the blunt end of the egg with a pin before putting it into the water")

Fortunes in formulas, for home, farm, and workshop 1939

Preserving and pickling eggs at home 1974

However, in 1939 Phillip G. Weimer invented the device illustrated below, Egg Venting Device (US Patent No. 2,224,941) and said:

As is well known, in boiling eggs, especially eggs which are initially at the relatively low temperatures at which eggs are customarily maintained in domestic refrigerators, it is a common occurrence for the shell of an egg to crack in the boiling operation. This results in the extrusion from the shell, and ordinarily the wastage, of a portion of the albumen of the egg. Furthermore, on the removal of the cooked egg from the cracked shell, it is ordinarily found that the appearance and frequently the physical characteristics of the egg have been impaired as a result of the albumen extrusion.

I have found that such cracking of egg shells in the course of the egg boiling operation may be eliminated by forming a small vent opening at the large end of the egg through the egg shell and the immediately adjacent membrane lining the shell and forming the outer wall of the air space at that end of a normal hens egg. If the vent opening formed is suitably small no albumen will escape through the opening during the boiling operation, and if the second membrane forming the inner wall of the air pocket is not punctured there will be no significant difference in appearance, or in` physical characteristics, between an egg which has been boiled after having its shell punctured in accordance with the present invention, and a similar egg boiled without having its shell first punctured or cracked in the boiling operation.

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In Australia, about 1972, the Egg Marketing Board for the State of New South Wales published:

NON-CRACKED EGG BOILING
At last I've found a way to solve the problem of eggs cracking during boiling. At least I haven't, but the N.S.W. Department of Agriculture assures me it has ! It's all done with a simple pin prick, although preferably with a special pin- gadget available at some supermarkets and hardware stores. The point (one-eighth of an inch long) penetrates the shell at the blunt end— the site of the air cell.

So the conclusion is that people misapplied advice that was meant only for artificially preserved eggs, to fresh eggs.

Natural chicken eggs are gas permeable according to Physiology of Domestic Animals so there is no need to prick an additional hole. However, in the case of Ladd's sodium silicate preservation method the pricking is needed to let the air out.

  • I love that your research has brought up a telling tale about how an urban legend was formed. I want to upvote it several more times. However, @Schmuddi's answer gives empirical evidence. With this answer, it isn't actually clear whether the NSW Egg Marketing Board happened to be right or not (or Ladd either, for that matter.) – Oddthinking Mar 19 '17 at 1:57

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