Testing: A sweeter sweet potato?

This Sunday I was preparing smoked legs of chicken. I had bought sweet potato to go with it as a mash. Idly googeling around I came over this blog:

http://www.seriouseats.com/2010/11/the-best-roasted-sweet-potatoes-thanksgiving-sides-the-food-lab.html

That post talks about how starch in sweet potato may be broken down into sugars for a sweeter taste. Interesting. Sweet potato contains lots of starch, and when heated up to around 57 degrees Celsius, an enzyme starts breaking starch down to sugars. Nice. The bad thing is that the enzyme stops working at around 75 degrees. So keeping the sweet potato within that temperature window for a longer time than normal when cooking will produce more sugars.

And what is the easy way of keeping stuff at relatively constant temperatures these days? Sous vide cooking. I peeled, diced and bagged my potatoes and placed the vacuumed bag in my water bath at 65 degrees.

The difficulty with this type of food, hard, edgy pieces, is that it is difficult to get all the air out. There will always be air trapped between the pieces as long as they cannot deform to squeeze it out. It may not look much, but once you pop the bag in the water you will notice a tendency to float. And as the air is heated, it will expand and you will see that it is quite a lot of it. So weighting down the bag may be needed, but this may also prove difficult. But one must try to make the best of it.

I had the bag in the water for about one hour before opening it and emptying the contents in a pot. The pieces were not soft enough to mash, so I boiled them until tender. I also had one sweet potato that had not been in the water bath. I boiled that one separately, as a control unit. After both batches were tender, I mashed them and finished them with butter, salt and pepper and served them both up.

Enter the jury in the form of my 17-year old daughter. She, I am happy to say, is also interested in food and is becoming a good cook. I asked her to taste both batches, and the judgment was clear. The one from the sous vide had more taste. It was sweeter, had more depth and, I think, was just better.

So pre-cooking the sweet potato in a water bath (or an other constant source of heat) at around 65 degrees Celsius for an hour or more will make the sweet potato sweeter and add taste to it.

Great stuff!