Trekquinox Interlude: sous-vide cooking and PIDs

Okay, before we roll up our sleeves and dive into the truly Modernist cooking bits, let’s pause for a bit of science and explain exactly what sous-vide cooking really is.

Sous-vide literally means “under vacuum” in French, and I emphasized that part of it for my dinner, since vacuum and space are clearly thematic. But truly, it’s not so much about the vacuum packing as about the constant and exact control of temperature. The vacuum sealing is just a means to that end.

Ask yourself why timing is so important in cooking. If you like a soft-boiled egg, you know to cook it for three minutes. If you want your stake medium-rare, you’d better take it off the grill at exactly the right time. Why? Because we’re applying a much higher heat than we really want the food to be at. An egg yolk that’s actually at 212°F, the same temperature as the boiling water it came out of, is green and crumbly and tastes of sulfur. Not at all what anybody wants. So heat is pouring into our food, and our job as cooks is to figure out when the exact right amount of heat has entered the food, and then take it out – it’s “done”. And that’s a tricky business. Not to mention that when the center of something has reached the perfect temperature, then the outsides are going to be much hotter. It’s pretty much impossible using conventional cooking techniques to have a piece of meat or vegetable be the exact same temperature throughout. So what if we could just set the temperature we want? A medium-rare steak should be 127°F internally. So if we submerge it in a bath of water (safely sealed in plastic with no air in it, so that the air isn’t insulating it and making the bag float, and so the water is actually surrounding the food and in total contact with it) and wait long enough for that heat to permeate your food, then it will be the exact right temperature. You can’t overcook it!

That’s the basic idea behind sous-vide. You dial in the temperature you actually want your food to be, drop it in, and after some number of hours your food will be exactly perfect. Also, you can afford to be sloppy on the time – while there is some breakdown of consistency if you leave it for hours and hours longer than is necessary (and that’s an excellent technique for doing ribs, as it happens), you can leave it sit for an extra half-hour or hour with no ill effects. Making it much easier to make everything else come out right. Also, you can fit a fair number of steaks in a hot water bath the size of a camping cooler. Need to cook steaks for 20 people? No problem; provided they all want theirs to come out the same “doneness”.

It’s worth noting that sous-vide is a slow-cooking technique. The nature of heat is that it flows from hot areas to cold, and also that it transfers faster where there’s a bigger temperature gap. An oven at 450°F cools fairly quickly to the point where you can safely touch the racks; it takes about the same amount of time to cool from “safe to touch” to room temperature, even though it’s dropped probably 330°F in the first ten minutes and only 50°F in the second ten minutes. The closer it is to room temperature, the slower the heat transfer occurs. So your three to four minute egg is a half hour sous-vide; steaks should sit for two to four hours depending on their thickness. But while slow, it will eventually reach your perfect, perfectly controlled temperature.

So for things that only need to cook for half an hour or so, like eggs, it’s easy enough to just fill your sink with water of the right temperature. It won’t lose enough heat to matter. For a few hours (as in for steaks), filling an insulated cooler and sealing the top will do the trick. You probably want the water a few degrees warmer than you need, to account for a little bit of heat loss. My Modernist Cookbook suggests that would work fine for a “tailgate” party, if you wanted to sous-vide steaks, without any other heating technology.

But if you’re in for the long haul – if you want to cook ribs for 72 hours, for example – you’ll need some sort of heater that can maintain an exact temperature. That’s where the technology comes in.

PID controllers
PID controllers

Earl captured this photo of my sous-vide rigs in action (well, one is mine; the other I borrowed from my friend Doug, as I needed to cook two things at different temperatures). Those boxes with the readouts are PID controllers, the green cable leads to the heating elements, and the tinier boxes are simply aquarium pumps, to force bubbles through the water to keep it circulating. Cool science! Well, cool technology at any rate. While by the standards of a normal dinner party this would be pretty ugly and best hid in the back room next to your washer and dryer, for my Star Trek dinner party it was just what the doctor ordered!

Those particular boxes are a brand called Sous Vide Magic (made in Canada by one guy named Frank Hsu; go local boy!) They are pretty clever, and flexible. For starters, the box is controlling the heater via a standard plug; you plug the heater in to the Sous Vide Magic box. This means if you have any kind of electrically powered heating vessel – a crock pot, a rice steamer, even a deep enough electric frying pan – then you can just plug it into this, dangle the thermometer into the water, and it will use your existing electric appliance to maintain the water at an exact temperature. This is pretty slick if you already have a crock pot of some kind.

Of course, the additional component (that would be the green cable and the heating plate it’s attached to, along with the aquarium bubbler) frees you from your crock pot and pretty much gives you the ability to use anything at all. Any big pot you own. Your kitchen sink. Any watertight cooler (which is all of them, pretty much). The bigger the container the more you want it insulated, so as not to burn out the heating element (which is possible in North America; European plugs draw so much power that they have no trouble keeping up with massive water heat loss). Really, if you’re going to invest in one of these machines, the additional $30 to pick up a cooler is trivial, and it’s absolutely the way to go.

The sous-vide part – what about the vacuum?

Okay, so what about vacuum sealing your food? Well, you can buy vacuum sealers and specialty plastic for it, and that works really well. Actually it’s great for storing food in the freezer too. But it’s not necessary – I borrowed Doug’s old one, but I didn’t need it for anything in my Star Trek dinner. You can just use a Ziploc freezer sandwich bag. For my baseball sirloins, I put in a tablespoon or so of oil (helps displace the last of the air) and the steak, and then lowered it slowly into a sink full of water. You wouldn’t want to use your sous-vide bath, as it will be hot enough to burn your hands. Just a sink full of pleasantly not-too-cold water. Squeeze out any air that’s trapped under the steak or in the oil. Lower it down until the top of the bag is still above water, but the zipper part of the Ziploc is just under the surface. Then seal the bag. There will be no air in it, and if you’ve done it right no water either. Voilà! Suitable for immediate immersion, or freezing for storage. Oh yeah – sous-vide works great straight from frozen too; just allot some extra time for the thawing, like an hour or so.

PID – Proportional, Integral, Derivative

So what exactly does that mean? Buckle your seat belts, because we’re approaching the on-ramp of math, where we’ll cruise for a short while before exiting wiser and more informed. Don’t worry, I shall make it as painless as I can.

In my engineering screen, I spelled out PID because I wanted it to sound all tech-y and science-y. But they are usually just referred to as PIDs. The calculus of them is actually horribly complex looking, but it turns out if you look at computer code designed to actually do the work, it’s much simpler in application than in the theory. As a computer programmer who hated calculus, I was soothed.

Okay, let’s imagine you’re driving your car while blindfolded. Anyone who’s reading, feel free to try this at home. You are listening for the sound of those “rumble strips” to tell you when you’re at the edge of the road. You’re cruising along, and from your left you hear the sound of the rumble strips, still fairly quietly – you’re close to the edge, and slowly drifting further onto them. So what do you do? You wrench the wheel over to the right as far as it will go!

Clearly that’s a dumb idea; you can picture how that ends with your car careening wildly between the edges of the road until you flip. Instead, you want to turn the wheel only as much as necessary. If you hear the strips softly, you’re just at the edge and you want to turn gently back. If you hear them loudly, you would turn the steering wheel more.

That’s the proportional part of the name. If something’s a little cold, you add a little heat. If it’s a lot cold, you add a lot of heat.

Okay, back to our life-threatening car. We’ve turned the steering wheel a little to the right, and the sound of the rumble strips is getting quieter. But we’re not getting off them fast enough. At this point, you make the decision to turn a little more, since what you were doing isn’t working fast enough for your liking.

That’s the integral part of the name. Ignoring the actual math derivation of the name, you’re ramping the speed up (or down) when things are going the right way but not fast enough (or slow enough) for your tastes.

Okay, back to the death race! We’re doing pretty well at this point; happily we’re driving through the Canadian prairies so the road is straight as an arrow for hours and hours of driving time. But we’re in an old Oldsmobile 88, and it’s got kind of drifty steering. When we steer gently away from the rumble strips, we’re fixing the problem, but too slowly. But when we try and turn just a little more to adjust the rate of change, the next thing you know we’re across the yellow line and dealing with the same problem on the other side of the road. The road is just too narrow, and we’re weaving back and forth, or oscillating. Well, if we were dumb we’d just keep bouncing from shoulder to shoulder, but we’re smarter than that. After a while we realize that if we don’t compensate quite as much, we can anticipate the “bounce” and account for it. With a little practice measuring the time between shoulders we can straighten the car out in the middle of the road and actually be driving straight for long periods of time.

That’s the derivative part of the name. It’s the part that damps down swings around the target value and settles into a stable equilibrium.

Right, that ends the math lesson! The point is, it will raise the temperature up to what you want by controlling the heat, and it’s smart enough to settle down at a constant stable temperature. Just what we need for our sous-vide cooking.

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