Monthly Archives: April 2017

Food processor Chocolate-Cayenne cake

It’s Debby’s birthday, so I decided I should make a chocolate cake. This was a last minute decision, and I wanted to try something more conventional than the chocolate genois cakes I’ve done in the past. But, lacking a stand mixer, I also didn’t want to do the whole “cream butter and sugar” think either.

Nigella Lawson had a recipe in the NYT a year ago that involves throwing all the batter ingredients in a food processor and blitzing it all together. That sounded easy, but I was thinking I’d tweak it in a couple of ways. First, following the general principle of making muffins, I’d do the wet stuff and dry stuff separately and mix at the end.

Wet works:

  • 2 eggs
  • 1.5 sticks room temp butter
  • 0.75 c buttermilk/yogurt (sub for sour cream in the original). I had some buttermilk that needed to be used up.
  • 2 t vanilla extract
  • 1 c sugar. OK sugar is a dry ingredient, but I want it to dissolve.

Dry stuff. Sift together:

  • 1.5 c flour. I used 1 c cake flour and 0.5 c all purpose. Not sure if that mattered.
  • 0.33 c cocoa powder
  • 1 t baking powder
  • 0.5 t baking soda
  • 1 t kosher salt (not in the original)
  • 0.25 t cayenne pepper (not in original)
  • 0.25 t cinnamon (not in original)

Processed the wet stuff in the food processor. The butter didn’t really fully incorporate at this step, it looked like curdled eggs. But that was resolved by adding the dry stuff and processing until smooth. The consistency was thicker than I expected. It was reminiscent of soft-serve ice cream.

Transferred to a 9″ ringform, buttered, floured, and with a circle of parchment on the bottom. I had buttered it to make sure the joints were sealed, but that wasn’t an issue with this batter.

Baked in a 350 F oven for about 50 minutes. I had set a timer for 35 based on the original recipe, which is for 2 8″ pans. Kept it going until a toothpick came out clean.

The cake had a distinct dome shape. If/when I do this again, I’ll try some of the tips from this site, starting with lowering the temperature and backing longer. The cake cooled while we went shopping and made dinner (Pan-fried Dover Sole in lemon butter with roasted baby potatoes and green beans) and watched the season premiere of series 10 of Doctor Who.

With the video on pause, and Debby feeding the cats, I brushed some framboise on to the cake and dusted it with powdered sugar. We weren’t in the mood for frosting. Served with some lactose free Breyers vanilla ice cream and some raspberries.

I think it was pretty successful. The chocolate flavor was strong from the cocoa powder and the cayenne and cinnamon added some nice warmth to the flavor. The texture was light, tender and cakey. On general principles, more liquor might have made it even better.

If the tips to make it flat work, this could be a nice base for a fancier presentation.

Sous vide black bean ribs

I had purchased some pork spareribs intending to try one of the previous rib recipes I’ve posted here, finishing them on a gas grill instead of in the broiler. But I procrastinated getting them marinated, and it’s been a rainy day here in College Station, so I decided to try a sous vide version of braised or steamed black bean ribs. I’ve made something like this in the microwave before, but the unattended timing of sous vide seemed like it would be worth trying.

Anova has done a sous vide version. I used their 167F temperature but improvised the rest based on what I’ve done before and what we have around on a day when we need to shop for groceries.

  • Ribs – cutting these into the desired shorter chunks was a pain (not having a bandsaw), so I only did some of them
  • Splash of soy
  • A handful of minced fermented black beans
  • minced ginger
  • Splash of fish sauce
  • Splash of dry sherry
  • Spoonful of chiu chow chili oil

Bag the whole thing and throw it in at about 1:15 PM on Sunday. Took them out and thickened the cooking liquid a little with corn starch, then served with rice.

It was pretty good, but a bit on the bland side. When I do this with chicken, I brown before braising. Neither recipe I looked at does that, but maybe it would have helped. Longer pre-cook marination, as recommended, might also have been good.

MacBook Pro connection confusion

Migrating from my old MacBook Air to my new 2016 Macbook Pro has involved some confusion about adapters and accessories. Overall, I like my new Macbook, but there have been a number of annoying things. The biggest is still Apple’s decision to kill the MagSafe power connector. More minor annoyances:

  • Out of the box, the brick used to come with a 3 prong extension in addition to the stubby 2 prong power connection. Now it’s extra.  The longer cable on the brick end is really valuable when you have a bunch of people (e.g. at a conference or students in a class, or even at an airport waiting area) sharing a wall plug or power strip. Fortunately, I can recycle a bunch of these from my old power bricks that don’t work anymore for the new MacBook.
  • If you buy the power brick you now have to buy a separate USB-C charge cable.  As far as I can tell, this should work with a generic USB-C cable. What was annoying here was buying a power supply at an Apple Store and not having the Apple employee ask if I needed the cable.
  • The original Thunderbolt was a superset of MiniDisplayPort, and Thunderbolt 1 and 2 used miniDisplayPort connectors.  There is a Thunderbolt 3/USB-C to Thunderbolt 2 adaptor, but although Thunderbolt 2 is a superset of MiniDisplayPort, the adaptor works for Thunderbolt connections but not for miniDisplayPort-based adaptors. In other words, plugging a Thunderbolt Display (discontinued in 2016, but some of us still have various versions) in works. What doesn’t work is MacBook-Thunderbolt adaptor-miniDisplayPort to VGA or HDMI adaptor-monitor.
  • If you want to sync an iPhone or an iPad to your MacBook Pro, you will need either a USB-C to lightning cable or a USB-C to USB-A adaptor. This means that if you buy a brand new MacBook Pro and a brand new iPad, you can’t connect them right out of the box. The USB-C to Lightning will allow you to use the MacBook power brick to charge an iPhone or iPad with or without the MacBook in the middle, so that could reduce the number of things.

 

More on cocktail thermodynamics

Debby found this post from Dave Arnold that resembles what I discussed in the last post. Shorter version: I’m probably wrong about the ice being close enough to thermal equilibrium for government work, but the explanation of what is going on isn’t quite the way I recall Weitz explaining it. And my old Intro Bio prof is still wrong.

Fact 1:Ice at 0°C can chill an alcoholic drink well below 0°C. This fact is counter-intuitive to many, but is an irrefutable consequence of the laws of thermodynamics.

Arnold does an experiment that is essentially what we saw on Friday night, using vodka instead of tequila. After pre-incubating ice in water, the water is drained off and vodka is added. He gets  slightly diluted vodka at -4.5 °C. He also did a measurement of how fast ice reaches thermal equilibrium:

Fact 2: Bar ice is almost always at 0°C unless it comes straight from the freezer. People have a hard time accepting this fact. As a test, I froze a large ice cube with a super-thin hypodermic thermocouple probe in the center.  I put that ice cube, along with some run-of-the-mill ice cubes for insulation, into a blast freezer for 4 hours until everything was at -20 C.  I then put the entire batch into a plastic container and waited.  In under 20 minutes, the large ice cube was within 0.5 degrees of zero.

In the comments to an earlier post, a reader wonders if he is measuring the core of the ice or surface water that develops around the temperature probe. Although the temperature might not be quite all the way up to zero for that reason, I suspect that the known conductive properties of ice mean that it’s closer to 0 than -20.

So why does this work and what’s wrong with my earlier analysis? Because I idiotically glossed over an important part of the Clausius version of the Second Law

Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time

The other change that is connected therewith to passage of heat is the breaking of bonds in the ice and the conversion of ice to water. Duh! As the vodka/tequila goes from 20 to 0, the heat is passing from the warmer liquid to the cooler solid ice, melting the latter with 333.55 J/g (80 cal/g). Melting a g of ice can chill 4 ml of water from room temp to 0.

But when the vodka/tequila is below 0 but above the depressed freezing point, melting reactions don’t stop. There are still a fraction of the total intermolecular collisions between the liquid and the ice that have sufficient energy to break the water-water bonds on the surface of the ice and melt off some of it (Not being an ideal gas, this won’t be a Maxwell-Boltzmann distribution, but there will be a mix of energies). This cools the liquid phase, just as it does when the collision occurs above 0°C.

Whether you are cooling water or liquor, the final temperature is still set by the freezing point, which is where the probability of a water molecule joining or leaving the crystal lattice is equal. So I think I’m still right that the freezing point depression is important. The ethanol isn’t doing anything to the heat exchange per se. It’s allowing us to see cooling below 0 when we measure the temperature of the liquid phase.

Arnold argues that the chilling is due to a combination of the heat that goes into melting and the entropic gain from diluting the water released by that melting into the liquid phase. In another comment he writes

Freezing point depression isn’t enough to explain why the drink gets colder than zero as you shake it. For instance, many oils have a very low freezing point but if you put an ice cube in them they will only go down to 0 degrees because there is no mixing.

I’m not crazy about this explanation, as it seems to me that it approaches Gibbs’ paradox territory with respect to the water released from the ice being diluted into the bulk vodka/tequila. Here, I think he’s seeing an effect of surface water around the ice cube limiting the temperature change. The observation about the melting points of oils does suggest a possible way to measure the internal temperature of ice cubes if one could suspend oil droplets in clear ice.

On the physical chemistry of ice cream and margaritas

When I was an undergrad at Stanford, senior biology majors were recruited to be TAs in the freshman biology class. I signed on for this and my first teaching experience at the undergraduate level involved attending lectures and leading discussion sections. In one lecture, the prof talked to the class about why salt is added to the ice in an old fashioned hand-cranked ice cream machine. He said, correctly, that the salt allowed the brine surrounding the freezing canister to get colder than 0°C, but that the mechanism was via the enthalpy of change solution of the salt dissolving in the water. I told my recitation section that the prof was wrong. The brine gets colder than 0°C due to freezing point depression, and that it was thanks to the ice starting at well below 0°C.

My questioning of his authority got back to the prof, who decided to add some material to a subsequent lecture to correct what he believed was his smart-aleck TA leading some of his freshmen astray. He pointed out that the enthalpy of solution for NaCl is +3.3 kJ/mol (or ~0.8 kcal/mol; we used kcal back then). I forget how much NaCl he thought was reasonable, but he came up with a back of the envelope calculation that disagreed with this

For each 58.44 grams (2.06 ounces) of salt that dissolves, 0.717 kilocalories (3 kilojoules) of heat is absorbed, meaning that dissolving salt causes the solution to become colder. The change is so slight you are unlikely to notice it in everyday life.

Fortunately for my prof, this was long before smart-ass students could use Google on their phones to find links to contradictory sources. And Wikipedia was far in the future. Saturated NaCl at 0°C is a 26% solution, which is ~4.45 M. So, starting with ice cold water with no ice you could drop the temperature to something on the order of 3 degrees. Which would eventually freeze the ice cream if you had massively excessive volume relative to ice cream, where you have to need a liquid to solid phase transition where the enthalpy of fusion on the order of 200 J/g (less than water, but still a lot relative to the heat of solution, according to this (pdf)).

So, in hindsight, I remain unconvinced by my old prof. I’ve often thought that one problem with intro bio textbooks is that they start with material that is taught more rigorously  in intro chem, by faculty who know the material better. I might have only been a freshman, but the elapsed time between when I had taken chemistry was decades shorter than it was for the ecologist teaching intro bio.

I was reminded of this experience earlier on Friday night, when I attended a very entertaining public lecture in the Physics Department, only peeking at the streaming video for the Stanford-S. Carolina Women’s basketball Final Four game on my phone a couple of times (Stanford lost, unfortunately… not enough enthalpy of shooting).

This was the event:

Now Harvard’s David Weitz is very different in background from a Stanford Ecologist/Intro Bio prof., and the elapsed time from my last physics/p. chem course is orders of magnitude longer than the last time he taught physics. Nevertheless, I think he made the same kind error as my old Intro Bio prof, and in fact I think his is worse in terms of the thermodynamics.

Toward the end of the lecture, he was using Peter Madden’s margarita preparation to illustrate temperature and phase transitions. In a shaker with ice and water, he asked the packed audience what they thought the temperatures were for the liquid and solid phases, i.e. the water and the ice. A young boy in the audience guessed that because they were in different phases, the ice was colder. He said something like: the ice is 31.999999 °F and the water is 32.000001 °F. Weitz said, no, they are both at 32 °F (or 0°C; there was a lot of shifting between C and F and I forget which). At that point, I leaned over to Debby and muttered that he was assuming that the system had reached thermal equilibrium, which was not knowable from the information provided.

OK, whatever… but then he had Madden pour out some tequila, which the measured as being at room temperature. They drained the water from the shaker, added the room temperature tequila, and shook it to mix. He then asked what people thought the temperature of the tequila would be. People guessed, they did the measurement, and lo and behold, it was significantly below 32°F/0°C.

What gave me a deja vu experience was his explanation of why the liquid phase was below the freezing point of pure water. We agree that the ethanol in the tequila is key. But unless I really misunderstood him both in real time and when I asked him about it afterward, he was arguing that the ethanol somehow allowed the liquid phase to lower the temperature of the solid phase! Which would require heat flow from the colder ice to the warmer tequila, looks to me like a flagrant violation of the Second Law of Thermodynamics.

This violation is only a problem if you think, as he insisted afterward, that the ice in the ice-water mix had reached thermal equilibrium and the solid phase starts uniformly at 0°C when the 20°C tequila is added. By contrast, if you agree with the kid in the audience that at least part the ice was colder than the final temperature of the liquid phase, there is no problem. The final temperature is just set by the freezing point depression from the ethanol and other solutes in the tequila.

The alternative hypothesis is that I’m misunderstanding what he said or missing something. This is plausible, because although it’s an appeal to authority argument, I think it’s a reasonable to think that a Harvard Physics Prof who specializes in phase transitions to have a higher probability of being right about this than me, a molecular biologist/annotation maven. Although I would estimate that the probability of me being right is still higher than the probability of getting a reservation at El Bulli before it closed.

But see the next post for an update!

Equation of the post:

ΔTF = KF · b · i,
where:

  • ΔTF, the freezing-point depression, is TF (pure solvent) − TF (solution).
  • KF, the cryoscopic constant, which is dependent on the properties of the solvent
  • b is the molal concentration of the solute
  • i is the stoichiometry of the solute: the number of particles per molecule in solution. For ethanol this would be 1; for NaCl, it would be 2.

From Wikipedia.