How taters taste: It's the starch, stupid
17 October 2007, 09:46
Paris - Call it the potato conundrum: why does one batch of homemade chips, or French fries, taste like deep-fried slivers of heaven while the next - cooked in the same kind of oil and at the same temperature - has all the allure of greasy cardboard?
Potato chemistry is a bedevilingly complex affair, and a small army of scientists around the world work full time on unlocking the inner secrets of the lowly spud.
US botanists even sent potato seedlings into orbit to see how they would grow in zero-gravity.
But for most experts the answer boils down, as it were, to one word: starch.
"Starch is the most important factor because it comprises about 80 to 85 percent of the dry matter in the potato tuber," said Anton Haverkort, head of the Plant Research Institute at Wageningen University in The Netherlands, and a giant in the world of potato research.
This knowledge does not necessarily make life in the kitchen any easier.
Some spuds are best baked or pan fried, while others lend themselves to boiling, though not, of course, necessarily for mashing.
Mismatching variety and cooking method has been known to lead to depression, divorce or worse.
The easy way to avoid traumatising potato failure is to buy your taters frozen, which means some industrial food-processing giant in the Netherlands or Idaho has picked and prepared them for you.
But any self-respecting home chef with the courage of his or her convictions will want to select their own spuds. And ignorance is not bliss, which is why one should not only know that a waxy Red Bliss holds its shape when boiled, but why that is so.
"A waxy potato is lower in solids and starch content, so when cooked, it has a moist feel in the mouth," said Kerry Huber, a scientist at the University of Idaho who calls himself a "starch chemist."
The general rule of thumb, he explains, is that high-starch potatoes, which have more solid matter and less water, are best for chips and baking.
"When you cook a potato, no matter what the method, two things are going on," he told AFP.
One is that tiny starch granules inside the potato cells expand and exert pressure on the watery pectin-rich medium, called the middle lamella, in which the cells are suspended.
At the same time, the heat causes the pectin to swell with liquid.
"Finally the middle lamella that is holding the cells in place breaks down," said Huber. "You get good cell separation and thus mealiness."
In potato parlance, "mealy" is good, corresponding to a fluffy, grainy texture in baked or mashed potatoes, and the crispy-on-the-outside but tender-on-the-inside texture of perfect chips.
Russets, Idaho, Saxon, Nadine and Binjte are all on the high-starch end of the spectrum, while Nicola, Charlotte, Red Bliss, French Fingerling and Red Creamers have lower starch content.
Yukon Gold, Yellow Finn, Purple Peruvian and King Edward are "in-between" or all-purpose potatoes.
But there is starch, and there is starch.
"A lot depends on the proportion of the two kinds of starch one finds in potatoes, amylose and amylopectin," said John Bamberg, a professor at the University of Wisconsin and Director of the US Potato Germ Bank.
Cell size also plays a critical role: the smaller the cells, the more surface area there is binding the potato tissue together, making it harder to break down.
And let's not forget the chemical nature of the pectin itself, which is held in place more or less tightly by long salt and acid molecules, he said.
Then, of course, there's sugar content.
Potatoes, it turns out, require more precise storage temperatures than a Bordeaux Grand Cru Classe: warmer than 7°C, the spuds will sprout and shrivel; colder than 5,5°C, the starch will turn to sugar, which changes the taste and causing discoloring when cooked.
"You have multiple factors that all contribute simultaneously to the way a potato cooks," said Huber by way of summation, pointing out that there is yet another factor that has nothing to do with the tuber itself: how long one cooks it.
"Abuse any potato, and you are going to get a mess. The cells break up, releasing their starch, which give you a translucent, pasty texture," said Huber.
And "pasty", in case you hadn't guessed, is bad.
Potato chemistry is a bedevilingly complex affair, and a small army of scientists around the world work full time on unlocking the inner secrets of the lowly spud.
US botanists even sent potato seedlings into orbit to see how they would grow in zero-gravity.
But for most experts the answer boils down, as it were, to one word: starch.
"Starch is the most important factor because it comprises about 80 to 85 percent of the dry matter in the potato tuber," said Anton Haverkort, head of the Plant Research Institute at Wageningen University in The Netherlands, and a giant in the world of potato research.
This knowledge does not necessarily make life in the kitchen any easier.
Some spuds are best baked or pan fried, while others lend themselves to boiling, though not, of course, necessarily for mashing.
Mismatching variety and cooking method has been known to lead to depression, divorce or worse.
The easy way to avoid traumatising potato failure is to buy your taters frozen, which means some industrial food-processing giant in the Netherlands or Idaho has picked and prepared them for you.
But any self-respecting home chef with the courage of his or her convictions will want to select their own spuds. And ignorance is not bliss, which is why one should not only know that a waxy Red Bliss holds its shape when boiled, but why that is so.
"A waxy potato is lower in solids and starch content, so when cooked, it has a moist feel in the mouth," said Kerry Huber, a scientist at the University of Idaho who calls himself a "starch chemist."
The general rule of thumb, he explains, is that high-starch potatoes, which have more solid matter and less water, are best for chips and baking.
"When you cook a potato, no matter what the method, two things are going on," he told AFP.
One is that tiny starch granules inside the potato cells expand and exert pressure on the watery pectin-rich medium, called the middle lamella, in which the cells are suspended.
At the same time, the heat causes the pectin to swell with liquid.
"Finally the middle lamella that is holding the cells in place breaks down," said Huber. "You get good cell separation and thus mealiness."
In potato parlance, "mealy" is good, corresponding to a fluffy, grainy texture in baked or mashed potatoes, and the crispy-on-the-outside but tender-on-the-inside texture of perfect chips.
Russets, Idaho, Saxon, Nadine and Binjte are all on the high-starch end of the spectrum, while Nicola, Charlotte, Red Bliss, French Fingerling and Red Creamers have lower starch content.
Yukon Gold, Yellow Finn, Purple Peruvian and King Edward are "in-between" or all-purpose potatoes.
But there is starch, and there is starch.
"A lot depends on the proportion of the two kinds of starch one finds in potatoes, amylose and amylopectin," said John Bamberg, a professor at the University of Wisconsin and Director of the US Potato Germ Bank.
Cell size also plays a critical role: the smaller the cells, the more surface area there is binding the potato tissue together, making it harder to break down.
And let's not forget the chemical nature of the pectin itself, which is held in place more or less tightly by long salt and acid molecules, he said.
Then, of course, there's sugar content.
Potatoes, it turns out, require more precise storage temperatures than a Bordeaux Grand Cru Classe: warmer than 7°C, the spuds will sprout and shrivel; colder than 5,5°C, the starch will turn to sugar, which changes the taste and causing discoloring when cooked.
"You have multiple factors that all contribute simultaneously to the way a potato cooks," said Huber by way of summation, pointing out that there is yet another factor that has nothing to do with the tuber itself: how long one cooks it.
"Abuse any potato, and you are going to get a mess. The cells break up, releasing their starch, which give you a translucent, pasty texture," said Huber.
And "pasty", in case you hadn't guessed, is bad.
Durban
IOL ENTERTAINMENT
IOL TECHNOLOGY
IOL JOBS
IOL TRAVEL
IOL MOTORING
BUSINESS REPORT
