The mystery of the wet potato

My favorite meal of the day is breakfast. So when I first started cooking my own meals, I decided to start with my favorites. This was generally a good decision since most breakfast foods are pretty forgiving for a beginning chef. I mean, it’s pretty hard to mess up a fried egg or toast. But one dish eluded me for the longest time: hash browns. This was both frustrating and a bit humiliating. What could be simpler than grating and frying a potato?  Yet my initial attempt produced hash browns with a charred, unsavory exterior and gummy interior.

The main player here. May not be the prettiest, but is an often necessary component of breakfast.

With time and practice, I eventually conquered the mighty potato. Through trial and error, consulting with Cook’s Illustrated (Sept/Oct. ’98), and the help of a friend in the restaurant business (ok, he was a waiter, but still), I discovered the three key “tricks” to perfect hash browns:

1) Squeeze out the water – no one wants a wet hash.

2) Only put a thin layer of hash on the pan – things get too crowded, and the hash gets soggy.

3) Take the amount of butter you think is healthy to use, and double it – this golden rule can turn almost any everyday kitchen feast into elegant fine dining. For potatoes, this has worked out to about 4 tablespoons of butter per potato.

The first two tricks were totally unexpected and completely interesting. When you had a thick layer of wet soggy potatoes in the pan, you were often left with a gummy, sticky layer of potatoes in the middle of the hash. To avoid this problem, I found that following trick 1 is more important than trick 2; wet potatoes almost never lead to a good ending, no matter how thick the hash.

Trick 1 came as a side note in a Cook’s Illustrated article (Sept/Oct ’98), but without explanation. I was curious why water was such an anathema to hash browns, in fact, I was surprised that there was so much water in potatoes to begin with. A decent squeeze of a small potato gave about 2 tablespoons of water- that’s almost 15% of the potato by weight, and that’s only counting the water that I was able to squeeze out. I guess it’s not all that high of a percentage compared to humans (we are 60% water by weight), but still, impressive for the starchy little guy.

When the potato is squeezed, we don’t just get water, we get a whole bunch of, well, stuff. The water is pretty cloudy and opaque, probably filled with starches from the potato. Interestingly enough, the water I squeezed from the potatoes turned brown over time. Peeled or shredded potatoes will brown when an enzyme in the potatoes is exposed to air. As a testament to my muscle strength, I apparently squeezed some of the enzyme right from the meat of the potato, causing the potato water to turn brown with time.

This water was squeezed from a peeled potato, so was not naturally browned by the color of the peel. Notice two things-first the top layer of water that was in the most contact with the air browned the darkest, and second that some white, probably starchy, stuff settled out to the bottom of the water. Pictures taken at five minute intervals.

Looking in from the top of the mug, the browning occurs quite spottedly.

This interesting point for me is that you squeeze a lot more than just water out of potatoes when prepping them for hashbrowns. This led me to a question: Is it water or the starches in potatoes that cause them to get their gummy, sticky interior?

This question screamed “science experiment” to me. The experimental design is simple- I grated three separate potatoes, one I cooked as is, one I cooked after a good squeeze, and one was cooked after a squeeze but with an addition of pure water. Everything else was kept constant- I used four tablespoons of butter in each test, and cooked each batch of potato hash for 7 minutes total: 3.5 minutes on each side with a flip in the middle.

Grated potatoes, ready for action.

This experimental design can test whether the gumminess is cause by the starch or water in the control. The third set of hash contains the same amount of water that was originally in the potato, but doesn’t include any of the starches that were also squeezed out of the potato*. This way I can test whether it is the water or the water + starches that gives the potatoes their gumminess.  If the water creates the gumminess, then I would expect the third test to be as gummy as the control.  If the squeezed out starches were causing the gumminess, then I would expect the third test to lack gumminess just like the squeezed potatoes.

The experimental design- every test included a potato, I just manipulated water and starch content.

The result, unfortunately, did not fit nicely into either expected answer. There was a clear difference between the control and squeezed potatoes. The control potatoes where definitely the gummiest, and the squeezed potatoes had little trace of gumminess, hardly holding themselves together at all. But the squeezed + water potatoes didn’t match either the controls or squeezed potatoes. They were really intermediate between the two- they certainly held together better than the squeezed potatoes, but didn’t have the full gummy texture of the controls. In other words, it seems as though both water and starches contributes to the gumminess.

Pangaea? When flipping the controls (left) and squeezed + water treatment (right) in the pan, I could retain one continent, but in the squeezed potatoes (center), the cohesive gumminess was absent and the continents of hash drifted apart.

Some further research found that this wasn’t entirely surprising- both water and starch are necessary to gelatinize (yes, that’s a word) starches, which basically turns starchy water in a visco-elastic substance (i.e., what I called a “gummy texture”). This probably means that the addition of water caused the starches remaining in the hash to gelatinize, but not as fully as the control which had more total starch content to begin with. My engineering side calls for measuring stress-strain curves of the hash browns to quantify this difference. But, alas, that will have to wait for another day.

* To be accurate, only some of the starches were squeezed from the potato.  Potatoes are quite starchy, and I’m sure that there was plenty of starch left in the hash.
Credits- All pictures taken by self.
Kevin Miklasz

About Kevin Miklasz

As a PhD student in Biology at Stanford University, Kevin’s research is on the biomechanics of micro-algae, as he clearly prefers academic obscurity to hot topic, sexy science. Besides cooking and doing science, Kevin also designs educational science games and engages in similarly nerdy interests. Kevin is an editor for Science Fare, and Director for Digital Curriculum at Iridescent.

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3 Responses to The mystery of the wet potato

  1. me November 22, 2011 at 11:53 pm #

    are bodies contain 79% water. Just giving you a little correction. Nice article by the way, very interesting.

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