About Copper: A History of Doing No Harm
It’s hard to imagine anyone consciously choosing contaminated food, right? While taking care with where their food comes from and how well it’s been handled in its travels, people have begun to think more carefully about the pots and pans in which they prepare that food too. Brooklyn Copper Cookware is pure, simple and as minimally processed as can be.
Which Lining? No Question. Tin on Copper
No cookware material, not aluminum, not iron, not ceramic, and certainly not stainless steel, conducts heat like copper.
“Copper is king here: It has nearly twice the thermal conductivity of aluminum… is five times more conductive than cast iron and 25 times more than stainless steel. Serious cooks love copper for this quality.”
Nina Shen Rastogi, Slate.com
The first thing you’ll notice when using tin-lined copper cookware is how fast it heats up. You just don’t need a high-output burner when you use copper – the 3500°F at the tip of any propane or natural gas flame is plenty of heat. Whatever source of heat you use with copper cookware (except induction, which only works with ferrous metals) you can count on the energy going into the pot, rather than bouncing off the bottom and going up the outside while the metal figures out what to do with all those extra BTUs.
We’ve tried copper cookware with all the available linings. There are a few options (including silver – amazing stuff. Still playing with that idea…) but as a practical matter only two are readily available: tin and stainless steel.
Get Hot Fast.
What holds true for electricity is also true for heat (for only slightly different reasons). Going geek for a moment here, but to give you an idea of the relative abilities of stainless steel and copper to pass energy through themselves: stainless steel’s thermal conductive coefficient, or k, is 16 watts per meter (kelvin), or W/mK. Copper’s k = 401 W/mK.
16 verses 401. Copper is 25 times more conductive than stainless steel. You can also read that as copper cookware using 25 times less energy to move the thermometer up a degree. Those high-output (i.e., energy wasting) burners? They came along in response to the use of high-resistance stainless steel cookware.
And yet lots of copper pots are lined with stainless steel in thicknesses between .5 and .75mm, just heavy enough to keep the lining from warping under heat. To match to the thermal efficiency of 2.5mm copper, stainless steel would have to be 25 times thinner than the copper outer layer – on a 2.5mm thick copper pot that would be .1mm; less than the thickness of a 6 mil plastic trash bag or heavy aluminum foil. Think about that. Your heat zips through a couple of millimeters of copper easy as you please, and then stops dead at a stainless steel liner to ooze up the sides for a while. Eventually the energy works its way through the stainless and then into the space within your pot, which is of course where you want it.
(And don’t get me started on ceramic, a material with some organic currency in the cookware business right now. Well, it is organic – clay comes straight out of the earth just like copper, and vitreous ceramic is completely molecularly inert under high temperatures. Ceramic is so thermally inefficient, however, that it’s most often used as an insulator; its conductivity coefficient 6.3 W/mK, 67 times less efficient than copper. One could say that, as cookware, ceramic is tailor-made for wasting energy).
Cooking: What’s Stainless Steel Got to Do With It?
Stainless steel dominates the world of cookware, from pots and pans to knives. Certain of its working properties are justly appreciated, mostly that it’s stainless (read: mostly rust-free). In the case of knives the trade off for rustproofing is that stainless neither holds nor retakes an edge as readily as the other principle knife-making material, carbon steel. The purpose of a stainless knife – cutting – and how well it does that task is subordinated to how it shiny it stays.
Stainless steel is a very hard metal, and that hardness resists taking on a fine edge. That same hardness and resistance accounts for why the wires in your walls are not stainless steel – as tough and resilient as it may be, stainless is worthless for conducting electricity – too inflexible and resistant. The wires in your walls are very likely made of copper, which conducts electricity with very little resistance. In fact, copper has the highest electrical potential of all the non-noble metals. We’re talking about cookware, however, and in cookware conduction in the name of the game.
Non-Toxic Non-Stick: Tin-lined Copper Lets You Off Easy.
Now, you’ve used stainless and have likely observed that it’s pretty sticky stuff – that’s why it gets lined with Teflon® and other polytetrafluoroethylene (PTFE) non-stick surfaces so often. A bare stainless steel surface grabs food like no other material; it’s an alloy of steel, chromium, nickel and often other metals such as molybdeium and titanium and has a very complex molecular structure. It resists seasoning like it resists energy; you cannot season a stainless steel surface like you can iron or carbon steel, both of which are comparatively porous but molecularly well-ordered.
Pure tin, on the other hand, is as non-stick a cooking surface as can be found, short of taking your chances with PTFE (speaking of linings that should never be heated empty). Food lifts off pure tin much as it does from well-seasoned steel, but tin does not require seasoning – its crystaline structure is already very smooth (i.e., molecularly simple and well-ordered).
Still, you can brown to your heart’s content in tin – it’s clingy in all the right ways. Perhaps you’ve noticed that on common PTFE surfaces water beads up – one of the reasons PTFE coatings don’t brown well is that the water in food does not sheet, it beads. In fact, one of the ways to tell your PTFE coating has degraded is that water begins to sheet rather than bead. The theory goes something like this: The relative failure of PTFE to brown under heat indicates you have a very thin layer of water consistently between your food and the cooking surface. Normally heat would tend to push water further into food (searing 101: moist on the inside, crunchy on the outside), but when cooking on PTFE normal thermal effects on water are partly compromised owing to the free electrons fluorine (the F in PTFE, and also in its toxic byproduct, perfluorooctanoic acid, or PFOA) makes available for molecular bonding with the hydrogen in water. Heat apparently activates more of these free fluorine electrons, thus creating a greater hydrophilic (hydrogen-bonding/water-attracting) effect. Water is drawn to create a barrier layer between the pan surface and your food, which has to literally steam a good deal before it dries out enough to begin to brown.
While it may be problematic for quality cooking, the hydrophilic quality of fluorine does keep the surface temperature of your PTFE lining closer to the boiling point of water, 100°C, which is below the level most authorities believe PTFE begins to outgas PFOA. So, by browning poorly PTFE keeps itself from hurting you.
There are, however, no such questions about tin. As we note all over this site, pure tin is molecularly and chemically inert – it does not react to variations in pH nor impart either flavor or volatile compounds to your food. It is not hydrophilic. It does very slowly oxidize (molecularly bond with oxygen at room temperature), turning darker with time, and it does impart some of those oxides to acidic foods, much as iron imparts oxides of iron when you cook in it. The net result of cooking in tin is you get a tiny bit more tin in your diet, an essential nutrient of which, in the last century or so, most people suffer a deficiency (tin-lined copper pots and tinned cans started being usurped by iron, aluminum and enameled steel about 120 years ago. Today a so-called “enamel-lined” can is very likely lined with bisphenol A-based plastic).
The point here is less to provoke concern than to attempt an explanation for why tin-lined copper has endured across millennia and why it’s so popular among serious cooks. Still, given what’s already common knowledge about the persistence of petrochemicals in the environment and in our bodies, we’re a little amazed that anyone would consciously choose to cook on plastic.
But, hey, that’s just us. PTFE and PFOE may indeed be no problem, despite being completely synthetic, environmentally persistent and, now, ubiquitous. The people who make the stuff at DuPont are a lot smarter than we are, and they say there’s nothing to worry about.
We agree; there’s no reason to worry, because, you know, it’s a done deal. That doesn’t mean we’re happy about having synthetic fluoropolymers sharing our cell space, so we’re just taking a different tack with our cookware. The worst that could happen using our tin-lined copper? You get a little more of an essential nutrient (you probably lack), and your sauces go three-star.
History Making: The Metal of Honor.
Make no mistake, we respect stainless steel. For bike parts and sailing tackle, if it’s not aluminum alloy or carbon fiber, stainless is what you want pretty much everywhere. For cooking there are better, more efficient, more culinary, less industrialized choices.
In the history of cookery, copper and tin have been at the forefront of every major step forward, not only during the Copper Age but like when the great Auguste Escoffier discovered that tin linings for canned goods would prevent the French army from dropping in its boots from botulism and lead poisoning. He picked up that fact from a study of how his copper pots and pans were made. That little advance netted him the Legion d’ Honneur, a place in history as the father of modern French technique (and as arguably the world’s first celebrity chef), and may have something to do with the tradition of copper being known as the chef’s “metal of honor”.
The first metal age was the Copper Age, and some of the first metal tools were for cooking. The first metal alloys were of copper and tin, leading to the Bronze Age. Copper and tin have literally accompanied mankind on our cultural path, harmonizing each step of the way with human needs and with the environment. This is no less true today than it was 7500 years ago.
We’re suckers for a good story.
Separation Anxiety? With Copper and Tin You Can Fuhgeddaboudit.
Tin, like copper, is many times more thermally efficient than stainless steel. That makes it a much better choice for lining copper pots and pans. Leaving an empty stainless-lined copper pot on heat will delaminate the lining (owing to vastly different expansion coefficients). It takes a long time, frankly a lot longer than it would take to damage a tin lining, but once your stainless lining delaminates, well, that pot, along with its copper, is ruined.
Likewise, the expansion coefficients of iron and the enamels that are often used to coat it are vastly different. Over time and repeated heating and cooling enamel will delaminate from iron, regardless of whether the pot was ever heated empty or not. Once that happens, that pot is a goner.
(Word to the wise: It’s never a good idea to heat any lined pot empty. Naked iron and carbon steel are about the only cooking surfaces that can be safely preheated without risking your investment.)
The one cookware lining that can be renewed to 100% good-as-new is tin over copper. Whether damaged or aged, copper cookware lined with tin can be restored time and again, making for a pot that will literally last centuries.
Your great grandchildren will thank you.
“Traditionally, of course, there is one ultimate kind of cookware, and it is made of copper which is becoming one of the rarer metals of the world. There is an enormous difference, however, in cooking pieces made of copper. There is the thin sort, which is of dubious value where good cooking is concerned. We’ve always considered one of the big ripoffs of our generation all that stainless steel merchandise with the copper-clad bottoms that was sold some years ago from coast to coast. And perhaps still is.
“In any event, the real treasure is solid professional-weight copper lined with tin… a solid copper stock pot with tin lining, pounds heavy saucepans of various volumes. The cost is a king’s ransom, but this is Tiffany-value stuff and will last well beyond the present lifetime of anyone reading this. The prices range from $20 for a charlotte mold to $185 for the stock pot, which includes an au gratin cover. The values will increase with time and in our books copper is a sound investment.”
Craig Claiborne, Craig Claiborne’s Favorites from The New York Times, 1975, p. 73.
Note: $185 in 1975 equals $850 in 2015 adjusted for inflation.