September 30, 2008

C6H12O6 → 2 CH3CH2OH + 2 CO2

A Lab correspondent recently wrote to us about his own experiments with vacuum pumps. And given our own work on the topic, I thought it would be useful to share his results. He pointed out that pumping per the manufacturers' recommendations (either until the pump returns strong resistance or starts to "click") might, in fact, be doing harm to your wine. Aggressive pumping will certainly provide a better vacuum and so reduce the effects of oxidation, but it may also serve to help pull ethanol out of solution and make the preserved wine smell "hot."

If you want to understand the hard parts of the science read these:

On the miscibility of Ethanol and Water (Science Beat); Wikipedia on Ethanol; and more on the effects of pressure on the solubility of gas.

If you read them (and I know you didn't), you know that yeast eats sugar and produces ethanol. It's the basis for making both wine and bio-fuels. Ethanol and water mix well but with weird results. Most relevant is probably that ethanol reduces surface tension in water. I say probably because I'm way over my head here science-wise and making most of this up. But it has something to do with the hydrogen's bonding properties and the reduction of system entropy that results. So it's not so much the pumping that's the problem, but the eventual release of pressure and the resulting disequilibrium that causes ethanol to evaporate out of solution and make the wine smell like grape-y diesel fumes. It's not dissimilar to what happens when you open a Coke and the gas, previously under pressure, escapes.

So we've been pumping less vigorously at the Lab (I know what you're thinking. Seriously, what's the matter with you? That is so infantile...) and the results have been positive (that's what she said!).

By the way, the guy who wrote us about this also makes a no smell, no taste, no residue soap just for wine glasses. We use it at the Lab. Check it out if you want.


Andrew said...

surely this fades to insignificance after pouring into the glass.

Chief of Lab Research said...

Hi Andrew, Not sure I follow what you mean. But if you're referring to preservation methods in general, I'd say "in the glass" is where it really becomes significant. And after running these experiments, I've been significantly impressed at what a difference good preservation makes. That said, as you may know, our policy at that Lab is "Open it, finish it." But we do try to community outreach in mind when planning our research agenda.

Chief of Lab Research said...

errata: "to KEEP community outreach in mind..."

Bombay Beauty said...

I've experienced something similar. This has led me to develop a new technique for pumping -- rather than gripping the pump solidly, I grasp it lightly and pull lightly with two fingers. I stop at the first sign of significant resistance.

I suggest future research on the best grip to use and the publication of safety guidelines.


Chief of Lab Research said...

Thanks BB,

As you can well imagine, we spend an inordinate amount of time working on our grips at the Lab.

A set of Safety Guidelines is a terrific idea!