Why should homemade oral rehydration solution not be boiled?
December 12, 2006 11:40 AM   Subscribe

Why should homemade oral rehydration solution not be boiled?

At work we just got pamphlets about what to do to prepare for pandemic flu. There is a recipe for ORS that calls for 2 T sugar and 1/2 t salt in a quart of water. After the recipe there is a note that says: "Do not boil the solution because that will reduce the solution's helpfulness."

How could boiling salty sugar water change it to the extent that it would not be as effective at rehydrating someone? The only thing I can think of is that some of the sucrose might be hydrolyzed to glucose and fructose, but I can't see why that would be a problem.
posted by oats to Science & Nature (6 answers total) 3 users marked this as a favorite
It would decompose (caramelize) the sugar. You can of course boil (then cool) the water before mixing.
posted by cerebus19 at 11:50 AM on December 12, 2006

@cerebus19 ... The only problem that I see with that explanation is that the carmelization point of sugar is significantly higer than the boiling point of water. According to the first authoritative-seeming source I could find "most sugar carmelizes at about 160 degrees Celcius, or 320 degrees Fahrenheit. This is significantly higher than the boiling point of water..."

So in order to carmelize the sugar, you'd have to boil off a significant amount of the water in the mixture in order to get it up to 320F.

But with that said, I don't really have a better explanation, except that maybe they're afraid that if people boil the water for too long, it'll alter the concentration?
posted by Kadin2048 at 12:03 PM on December 12, 2006

I imagine if you overboiled it, you could eventually raise the concentration (as Kadin2048 said) enough that it would actually do more harm than good. Obviously it wouldn't get to the point of being like drinking sea water (a bad survival tactic), but it might concentrate to the point that you start dehydrating.
posted by nekton at 12:06 PM on December 12, 2006

Best answer: Oral hydration solution takes advantage of a peculiarity of the foregut: it can absorb water *without expending net energy* if the osmolar strength of the gut contents are correct. Boiling can hydrolyze the sucrose, as you point out, changing the osmolar strength; also, if you boil for any length of time, you'll lose water, concentrating the solution and again altering the molarities of the various solutes.
posted by ikkyu2 at 12:09 PM on December 12, 2006

Response by poster: Thanks, ikkyu2. I should have considered the change in osmolarity with more solute molecules.
posted by oats at 12:38 PM on December 12, 2006

As ikkyu2 pointed out, heat can hydrolyze sucrose. Sucrose is a di-saccharide meaning it is molecule that is composed of two mono-saccharides, sucrose and fructose. When you heat the solution, the each sucrose sugar molecule splits into the two glucose and fructose molecules, a process called hydrolysis. So now you have twice as many sugar molecules in your solution. This changes the ideal molar concentration required for absorption.

By the way, the same process occurs if you put identical amounts of table sugar into hot tea or cold tea. The hot tea will taste slightly sweeter because it has more sugar molecules due to hydrolysis of the sucrose.
posted by JackFlash at 5:37 PM on December 12, 2006

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