Saturday, December 05, 2009

Wish I brought my camera cable...

Up in the Berkshires for a wedding, where it is beginning to gently snow. Two things: Glad I drove the Yukon. Wish I brought the cable that would allow me to post pictures of this pretty resort.

Update: Wish I remembered my bathing suit too. They have a great indoor pool--the cleanest I have ever seen at a hotel. They have trunks on sale in the gift shop but two things: They were expensive and I have maybe half dozen at home, so it is not as if I would get much use out of a new one other than today.

Monday, November 30, 2009

How much pressure can a fermentation achieve?

This ought to be known since, in principle at least, it is a pretty simple experiment to envision. However, I have done a bit of searching on Pubmed and found nothing on this subject. There could be a couple of good reasons for this: 1. It could be such a well known thing that a published paper would be pointless. 2. There is no practical need to find out an answer to this question. Makers of sparking wine already know how much sugar to add to get the desired level of carbonation and avoid exploding bottles, so what more is needed?

Well, I am interested out of pure curiosity. But how to do the experiment? One could fill a strong tank with juice and yeast, then close it up and keep track of how high the pressure gets. One possible complication is that the yeast may run out of sugar before the pressure stops them. Or the alcohol may get so high that this kills off the yeast. Or the Carbon dioxide in solution may cause the pH to drop to levels that kill the yeast. A couple of these things can easily be eliminated, depending on what happens: Let's say the fermentation slows to a halt at 200 psi. We relieve the pressure and then close-up the system and it again builds to 200 psi. This would show that the alcohol is not too high and the sugar is not limiting. What about the pH? When you vent the reactor the CO2 will leave and the pH should be able to climb. The only solution I see to this would be to have a neutralizing agent in the mix, perhaps a bit of Sodium bicarbonate for instance.

Part of what interests me about this is that I don't have a good feel for the relationship between delta G (or the energetics of a reaction) and pressure. Surely it takes energy to generate pressure, so at some point the reaction would stop at some pressure. There are also concentration effects in chemical reactions. We have Sugar going to Alcohol + CO2 and this reaction gives-off energy. If neither the Alcohol nor CO2 harmed the yeast then at some concentration, the mere excess of either of these would slow and then stop the reaction from moving forward. This is Le Chatelier's principle.

The technical term for it is wine

Over the Thanksgiving holiday I made a little bit of hard cider. This is very easy to do: You just put yeast into a bottle of apple juice--having first made sure it contains no preservatives. Preservatives do their thing by stopping the growth of yeast, among other things.

I like my hard cider to be bubbly, so I do the fermentation in the original bottle with the cap on tight. One must remember to relieve the pressure fairly often so that the bottle does not explode though!

The first batch was going well, so when it was close to being done I started a second batch by pouring a little of the first batch into the new one.

I was relating all of this to a few of our younger guests (high school and college aged) and suggested that when this last apple batch finished, I planned to inoculate a bottle of white grape juice. It was purchased for a party, it didn't get drunk and our kids don't like it--so it seemed like a good way of getting rid of it.

"Wait"! One of the young guests said, "You can ferment grape juice"? He may have regretted the words before they were fully out of his mouth: Not due to me though. I am gentle on youth. I said something like, "Yeah, sure you can". rather than the title of this post. And yes, I did think of the mean answer before I replied.

Sunday, November 29, 2009

Dahlia turned 10 on the 23rd but we had her party today

It was a bowling party in "mood lighting". Hence the psychedelic picture.

Where the office used to be

This spot is where our home office has been for the last 8 years. Now that we have a new office, posted about in the last week or two, the original is being pressed into family room service. Wasting no time, the Christmas tree is installed. This year a live one that we can plant outside after Christmas. My wife did all of the decorating with my one contribution being the addition of glass blocks to give a little more height.