A minimal jargon explanation, by Herr Direktor Funranium. Written while consuming a carbonated, no H2O Manhattan. Standards of insobriety, with corresponding misspellings and grammatical errors, are being upheld.
The stupid simple, “Go away, yer botherin’ me, boy” explanation of how a dewar works is that it’s like a really, really good scientific-grade Thermos(TM). The average person will nod and walk away, no better informed than they were a moment before. That kind of behavior encouraging ignorance is inexcusable and is dragging down the march of progress. We at Funranium Labs wish to enlighten…and drink. When combined, drunken enlightenment of others is also known as raconteurism. Telling a tale while wildly gesticulating, cocktail in hand, is the way we roll here. I seem to have gotten distracted. Where’s my drink?
Anyway, it would be more proper to describe a Thermos(TM) as a cheap commercial knockoff of a dewar. I’ll let the Thermos(TM) wikipedia article defame them properly for me. A beverage container that was a vacuum no better than a tenth of an atmosphere is hardly better than the old styrofoam beer can cozies. They rely primarily on the coefficient of thermal conductivity of select, proprietary insulating materials (usually a styrofoam-like substance) to minimize thermal transfer from the ambient atmosphere to your drink. Ah, I may have lost you there. Let us take a trip down High School Physics Memory Lane. Please make certain you are wearing pants before wandering the hallways and classrooms of yesteryear…*BEGIN WAVY LINES OF FLASHBACK*
There are three ways to transfer heat from one body/location to another. They are conduction, convection, and radiation. As we flip to the end of the chapter of definitions:
Conduction: transfer of heat directly from body to another by molecular motion. This is entirely dependent upon the physical/chemical properties of the materials in question on how well heat transfers from one body to the next.
Convection: transfer of heat by mass transport of warm fluids/gasses mixing with cooler ones. See Also: your oven (no, not your mom. I know you were expecting that joke though)
Radiation: transfer of heat by the emission of energy from a warm body as electromagnetic radiation (i.e. light).
Now, let’s review why dewars keep things at a constant temperature, not just cold. To the extent that you can reduce the three modes of heat transfer, you keep whatever at its starting temperature longer. The whole point is to keep temperatures as constant as possible; this is why another term for a dewar is “cryostat”. If it is hot coffee, it stays hot. If it is a frosty Manhattan, it stays refreshingly cold to the last drop. How does it reduce the transfer?
- It is made of two layers of material that are very good insulators (don’t conduct heat) with a seriously hard vacuum in the space between them.
- It comes with a lovely insulating foam lid.
- It is silvered on all possible surfaces containing the fluid.
Good scientific grade dewars are built of borosilicate glass which is fairly good about not conducting heat compared to metal and plastic (see also: most beer cans and cheap thermoses), reducing heat transfer by this route. Similarly, you need a vacuum to prevent both conduction and convection; if there is nothing there with which to conduct heat or convect, then you won’t have conduction and convection in those directions. Good quality scientific dewars will have a vacuum at least as low as .0000001 atmospheres of pressure, as opposed to the 1 to .1 atmospheres most Thermoses are (an atmosphere is defined as the outside air pressure at sea level at standard temperature, 68°F, and 20% relative humidity). The silvering is to help reflect all energy that your fluid could be absorbing from or emitting to the outside world, reducing radiation. Really, the only direction to thermal transfer via convection of warmed or cooled air, conduction to the air/fluid interface or radiation into open space is straight up from the top of your fluid. If you slap a decently insulated lid on top, well, you haven’t eliminated all of those but you’ve reduced them as much as you can such that you can still drink your beer.
How well does all this work, you might ask? At sea level, liquid nitrogen (AKA: LN2 for people in the biz) exists as a -196°C/-321°F fluid; it readily boils off in seconds when poured on the normal room temperature floor, which tends to crack the floor tiles and makes the maintenance staff grumpy. As a cryotech, I am very familiar with the situation where a bench top dewar by is sitting on the counter filled with LN2, lid on, and will still have LN2 in it three days later… much to my surprise when I bumped into it by accident.
THAT is why I use dewars to make these steins.
Coffee Science is a forever advancing field. Like other disciplines, it comes in fits and starts, though this could be due to caffeine. Even more important is the role of happenstance in the advancement in the body of human knowledge; the headscratching declaration of “Huh, well, that wasn’t supposed to happen.”
This last Sunday, I went to decant a delicious taste of Kenya BBotE that I’d prepared earlier in the week from one of my many storage Erlenymeyers. To my great distress, the ground glass stopper refused to give, denying me the caffeine boost I so desperately needed after a night of sea chanteys aboard the S.S. Balclutha. Crisis! Brute force did not work, so I resorted to physics.
I ran the flask under the hot tap for a couple of minutes in the hopes that the expanding vapor in the head space would pop the stopper. No such luck. Frustrated, I then placed the flask in a boiling water bath and patiently waited. *Insert Adages Of Pots And Boiling Water Here*
Thirty minutes of boiling later, I finally free the stopper. I take a sniff of the BBotE just to see if boiling harmed it. Oh dear, it smells like the finest of burnt Army Grade sargeant coffee. A taste confirms the smell: revolting.
BUT, this is a valuable learning moment. My previous hypothesis that my cold extraction technique preferentially extracts somethings and not others may still be valid. This little misadventure instructs that the horrible burnt coffee flavor is the result of prolonged overheating of the coffee, regardless of methodology to generate it. Whatever decomposes in heat to create this flavor is present in perc coffee, espresso, and the Black Blood of the Earth. It reinforces my directions on serving preparation: add BBotE to hot water, don’t boil BBotE on the stove, and if you’re gonna have it straight but want it warm, don’t over microwave it.
RECENT DEVELOPMENTS (3/7/10): BBotE vs. Analytical Chemistry FIGHT!!!
So, last week I finally got some quantitative analytical work done on the BBotE courtesy of some chemists who demanded to know exactly how much caffeine they were consuming and why it was so tasty. Thus far, I’ve only had the qualitative results of “Yup, sure seems to make people awake in small quantities.” We’re getting down to brass tacks here and asking how much for the monkey.
First, let’s revisit a toxicology concept known a Lethal Dose, or LD. It is normally quoted like this: LD 50/60. This translates as the acute dose that will kill 50% of the exposed unfortunates (see also: the title of my friends page) within 60 days. This *does not* mean that 50% is all that dose will kill, but it is important to put a milestone for measurement and at some point it is hard to tell if it is the acute dose that killed or something else. Also, this only works for acute dose; chronic exposure is a lot more difficult to quantify. In general, acute dose is organ failure, chronic dose is cancer.
For caffeine the LD50 is 192mg/kg of body weight in rat. It is somewhat concerning to me that the second suggestion from Google when I type in LD50 is “LD50 caffeine”. A normal 7fl.oz. cup of coffee contains between 110-170mg of caffeine depending on the varietal and how much robusta bean they snuck in on you. The standard toxicological model 70kg man would need to drink in the neighborhood of 90 cups of coffee to achieve LD50. Keep in mind that some people are “weak rats” and their lethal dose threshold is considerably lower. Still, that’s a lot of coffee. Just think of all the urination involved with that much fluid!
Okay, now that’s out of the way. For the experimental set up, I made preparations of 24, 48, 72, and 96hr steeped Kona all from the same batch of beans to check time variation in caffeine quantity. From the remaining beans, I also made a small pot of perc coffee and espresso to then test the BBotE against different preparation methodologies. Sadly, the espresso sample did not make it to the lab for analysis. 5ml of each sample was then placed in a small vial and allowed to evaporate in a fume hood. Once this was done, the dried residue was brought back up in a solution of methylene chloride preparation for sample loading into the gas chromatography (GC) unit.
Observations during sample prep:
1. Before serving, I generally recommend people shake the bottle before pouring. The 24hr sample was the most “frothy” with decreasing frothiness with time. This went counter to expectation as I guessed that longer exposure would draw more oils out causing this effect.
2. The light transmissivity was directly proportional to time in solution. The longer the sample had been let steep, the more opaque it was.
3. The evaporation rate was directly proportional to time in solution. The longer the sample had been let steep, the longer it took to evaporate. Strangely, the perc coffee sample took the longest to evaporate.
4. None of the BBotE samples moldered while exposed to open air, though the perc coffee did so within two days.
Figure 3: Samples in methylene chloride, with color gradient presented
The samples were presented to the GC lab manager, along with a complimentary bottle of BBotE in thanks for letting us abuse her machine. After a brief training run using ethanol blanks, we ran ran the 24hr sample and saw a really nice sharp caffeine peak comes up on the trace. At this point, I left the lab and handed control of the machine over to the Funranium Labs Staff Chemist. He ran the 48hr, and saw slightly a lower peak…hmm. So then he ran the perc and also saw a lower peak than the 24hr. With some head scratching, he ran the 96hr.
Have you ever played with an oscilloscope and turned the gain up too high such that you lost the top of the peak and looked squared off at the top? Well that’s what we had. It was around this time that the GC lab manager came back in, declared HOLY CRAP!!! and ended the run. She then looked with concern at the trace, then the bottle of BBotE I had given her, and then asked my chemist, “How much of this do I drink to *not* die, because this is awesome.”
And thus she was welcomed to the Esoteric Order of Funranium Labs Test Subjects.
I learned this all by my chemist reporting to my office with a hangdog look on his face. “I’ve got some bad news and some good news, Phil.”
Phil: “Okay, what the bad news?”
Chemist: “There was so much caffeine it over-saturated the detector and probably blew the calibration.”
P: “Crap. What’s the good news?”
C (jumping up and down with glee): “There was so much caffeine it over-saturated the detector and probably blew the calibration!”
We’ll be trying again next week with a 10000:1 dilution in hopes that we’ll get a number that we can use, rather than a borked machine. I am finding it likely that I will need to make an LD50 statement on future bottles of BBotE rather than the imprecise “High Caffeine Content”.