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Hard-Boiled Science

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Hard-boiling and dyeing eggs offers a number of avenues for families to explore both food science and chemistry. Forgoing boxed dye tablets, the eggs shown above were dyed using natural ingredients like turmeric and beets. Photo: Whiteley Creek, used with permission.


We hard-boiled and dyed eggs over the weekend, and the process opened up unexpectedly fertile ground for scientific exploration in my house. A simple, early-morning Google search clued me in to the fact that for at least a decade, I've been boiling my eggs incorrectly. Not only that, but according to my quick from-the-chair research, it seems that all my life I've been unwittingly eating overcooked hard-boiled eggs. I thought that sickly green layer to the yolk was simply... a fact of a hard-boiled egg. It's not! And the smell? Are you familiar with the sulfur-smell that often accompanies the hard-boiling process (or your Easter morning memories)? Only if you are also a victim of what may very well be the over-cooked, hard-boiled egg syndrome.

Newly aware of the fact that hard-boiled egg yolks should have beautiful sunshine-yellow-orange insides, I scanned a few online sites only to realize that there are dozens and dozens (to the power of Google) of supposedly "tried-and-true" ways to hard-boil the perfect egg. Few of them agree on the specifics, but they all agree that the yucky green color is not the goal.


Weekend Kitchen Science

I tend to be a bit over-cautious about cooking times, and I don't have any reason to willingly eat undercooked eggs, so I was a bit unsure about hard-boiling for considerably "less" time than I've done in the past. (It has since been pointed out to me that when frying eggs... I do leave the yellows slightly runny, so there's no logical reason to defend over-hard-boiling.) Given my food-bacteria-paranoia, and faced with scores of varying approaches, I decided we would try two different hard-boiling methods... and see how each turned out.

Obviously, we had a science experiment in the making! Later, when we dyed eggs, my 10-year-old was quick to understand that in order to evaluate the results, we needed to keep track of which eggs were which, so we assigned one batch of eggs to the orange, red, pink tubs and the other batch of eggs to the blue, turquoise, green, and purple tubs.

Our exploration didn't end there, however. When it comes to raising science questions worthy of Saturday-afternoon family exploration, we were on a roll. When you dye eggs, you're supposed to add vinegar to the mix in order to maximize the intensity of the dye. The pH of the vinegar affects the binding of the dye, but most instructions call specifically for white vinegar. As things often go in my house, my initial search of the lazy Susan cabinet (you know, the one that spins around and has cans stacked two or three high and a dozen or so buried inches back) didn't turn up white vinegar. What I did turn up was two bottles of apple cider vinegar, a salad dressing favorite. Frustrated that I couldn't find plain ol' vinegar, but aware that two kids were waiting to dye the requisite eggs—and trusting that I had what it took to make the process work—it seemed we'd have to give it a try.

Given that changing the pH of the water is the point of adding vinegar to the dye solution, apple cider vinegar should work, but would it work? Would the color of apple cider vinegar change the color of the dyes? Would the "sweetness" of the vinegar change the effectiveness? Did we really need yet another science experiment in the same day?

Luckily, I had two sets of dye tablets, and so we started out by prepping a set of dye baths for all colors using apple cider vinegar. We waited for the tablets to dissolve. We added the water. We submerged the eggs. A few minutes later, the eggs seemed to be taking on no color at all. It seemed like the apple cider vinegar not only wasn't working... it almost seemed to be interfering with the process. With a bit more searching, voila, I turned up a bottle of white vinegar, and we started again. I prepped a single new dye bath with vinegar, and we watched the reaction as the white vinegar began dissolving the dye tablet. There was pronounced fizzing and bubbling... which we had not observed with the apple cider vinegar.

With a small quantity of household Easter eggs at stake, I made a decision... scrap the apple cider vinegar. I dumped all the initial baths, rinsed the little plastic, egg-shaped tubs, and made new dye baths with white vinegar. Had we truly been going to document our results, we'd have run our trials side by side. But we didn't have that many hard-boiled eggs ready and waiting!

In the end, we had a handful of dyed eggs. They weren't Martha Stewart-worthy, and even with white vinegar, we didn't get the dye intensity we'd hoped for. It's something we'll explore again though! And next year, maybe we'll try more natural dyes, like the ones you can achieve using turmeric powder, beets, cabbage, and other natural plant-based ingredients. (I wish I'd seen these eggs earlier!)

In reality, the apple cider vinegar should have worked. Science Buddies staff scientist, Sandra Slutz confirmed for me Monday morning that using it in place of white vinegar should have been fine. "Making the water more acidic is what matters for increasing the dye uptake," she told me. I was maybe too quick to give up. If we'd had pH strips on hand, we could have furthered our informal study by comparing the pH level of the two vinegars. All things considered, it sounds like our dye experience is a good starting place for a longer, more controlled experiment.


The Proof is in the Yolk

And how did the hard-boiling turn out? We didn't know until the next day when we cracked and peeled eggs from each "method." Was there a difference? You bet! We had one set that sported the well-known sickly green ring. And we had one set with sunny, yellow-orange yolks. We noticed something else, however... the sunny ones were much, much harder to peel cleanly. (Okay, they were impossible to peel cleanly. Do you have a guess as to why? Have a hypothesis? Any thoughts on what you'd need to do to ensure your testing is controlled?) There's definitely room for some further exploration of hard-boiling and of the difference the "age" of an egg makes on the end result. And obviously there's room for a more formal experimental process! But we were excited about what we did—and about how things turned out.


Making Connections

With the egg hunt in my house over (and, ironically, we hunt plastic eggs—we dye eggs out of a sense of "you're-supposed-to" tradition), I poked around on the Science Buddies website today to see if we had a project that would have given me the golden key to perfect hard-boiling. What I discovered is that we have a project that deals with soft-boiling. So if you're interested in eggs... you might just find an egg-citing project in Egg-cellently Cooked Eggs: The Process of Soft-Boiling an Egg. Or... create your own variation with hard-boiled eggs. Or... tackle the dyeing process and see what it takes to get dazzlingly bright dyed eggs!

Something else came to mind, as I watched the dye tablets react with the vinegar in our little plastic containers. The dispersion of the color was immediately clear, and you could watch the tablet as it fizzled down, smaller and smaller until it disappeared. As I watched, I thought about a set of projects on the Science Buddies site that create a pretty amazing visual display of chemistry... a swirling, color-changing display, in fact. The projects are a duo involving the Briggs-Rauscher (BR) reaction:


What's really interesting about these projects is that the reaction is what is called an "oscillating" reaction. It doesn't simply go from A to B and then stop, as many reactions do.

From the project:

Most chemical reactions ... move in one direction, from reactants (starting chemicals) to products. In this chemistry science project, you will experiment with a rare and exotic reaction that oscillates. The reaction products appear and disappear for a number of cycles. Because the products are colored, the solution appears alternately blue, then yellow, then clear.

There's definitely room in this project for a "wow that's cool" reaction from a class or a group gathered for an informal science experiment!


[Science Buddies encourages adventures in family science, even when they don't turn out as expected! For tips and suggestions on making more room for science exploration and discussion at home, check out our Science Mom's video appearances. And be sure to browse our list of science projects perfect for the weekend.]

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