That vibrant beautiful green color in nature that really epitomizes life and ultimately is why we’re all here. Chlorophyll, as the fundamental key to Photosynthesis, is the wonderful little molecule that could. It’s of course so unfortunate then, that once the organism that owes not only it’s beautiful color but also its life-sustaining properties to said molecule is harvested and turned into food, the clock starts ticking before that color is gone. Any cook, professional or otherwise can attest to the fragile and fickle nature of this pigment, but if you were to ask a hundred such cooks why it is so I’d be shocked to hear even a single one of them give a terribly satisfying response. I’ll tell you right now that it’s really not that difficult.
At the highest levels of culinary excellence, the more stunningly pure the greens in your cookery are the better. Though it’s easy to think of this as a purely aesthetic consideration, it is also unfortunately the case that the degradation of that aesthetic is also quite strongly associated with a noticeable change in taste and aroma. Let alone the fact that we really do eat with our eyes first and what our eyes see has a meaningful and measurably significant effect on how we experience the flavor of what we’re eating.
As it just so happens, the breakdown of Chlorophyll is actually very simple to visualize. The diagrams I’ve seen of the molecule itself evoke an image in my mind of a royal Emerald Sceptre. Where the emerald represents a Magnesium Ion. If said emerald (Mg++) should be stolen the Sceptre must of course lose its lustre. As contrived and frivolous as this analogy might seem, I like it and hopefully in a minute you’ll understand why.
Ultimately, in cooking the preservation of Chlorophyll boils down to 5 considerations 1) Temperature, 2) Enzymes, 3) Ph, 4) Metal Ions and 5) Photo-Oxidation and in practice, you’re mostly worried about the first three considerations.
So let’s start with Temperature. It’s simply the case that, all else being equal, the hotter your food is, the faster the breakdown of the chlorophyll. In my analogy this would be like abusing and violently shaking the sceptre until the emerald falls out. It’s not the case that a specifically high temperature simply destroys all the chlorophyll all at once. If this were true then blanched asparagus would lose its color the moment it dropped in the water. It’s more accurate to say that the higher the temperature the less time you have before the emerald(Mg++) is gone. With this in mind you have your first bit of advice.
If you’re going to be cooking something green, Be Quick. Bring it up to cooking temp quickly, hold it at that temp only as long as absolutely necessary, and cool it down as rapidly as possible. If you’re not cooking it, keep it as cold as you can.
Next let’s talk about Enzymes. In nature and in the kitchen, this is always going to be at the forefront of the potential causes for Chlorophyll Degradation. Not only is there and enzyme called Chlorophyllase that will do the job but there are also a whole slew of more than a dozen different enzymes, naturally present that will do the same. In the analogy these are the greedy palace guards, the ambitious court members, and the jealous royal family all waiting in the wings for the first sign of decrepitude and weakness in order to make their move and rob the sceptre of its dazzling Emerald(Mg++). With regard to the actual science, what I’m describing is more or less called senescence where some sort of degradation of the plant cells triggers a dying process and all of these enzymes are released, with their first step being to remove or replace the Magnesium from the Chlorophyll. On a positive note it’s very easy to neutralize or destroy enzymes, just cook them. If that’s not an option then do whatever you can to keep your green food from withering, bruising or rotting. This would be the first signs of weakness so to speak that would tell the greedy and envious enzymes that now was there time to strike and when the first enzyme makes the first move that’ll signal more to try their shot and so on.
To neutralize enzymatic activity you can bring the food up to 85C/185f. You needn’t hold it at this temperature but merely make sure that the entirety of it has reached this temperature. If this is not an option then do what you can to prevent damage to the food which would trigger a cascade of enzymatic breakdown.
Alright so now we’re on to Ph or how acidic something is. For me this is often one of the most strikingly rapid and obvious ways of destroying the green in your food, which is weird considering how many foods there are that are simultaneously sour and green, Lime and Kiwi. The thing to note here is that theses foods are complex parts of living organisms that have thousands of structures that are incredibly well organized and compartmentalized. Once you process that organism into food, much of that delicate balance and order simply goes out the window. Ph is a measure of how much hydrogen ions are floating around in some amount of water. In the analogy this would be like a mischievous court jester, swapping out the emerald for a cubic zirconium. The more acidic the food, the worse the Jester gets. So then it also happens that going in the opposite direction helps out immensely. As it just so happens, this is easily accomplished with some baking soda and gives us our third rule.
Wait until just before serving to add any acidic ingredients to your green food. If the food you’re making isn’t sour then try making it more alkaline. When blanching something green add 1g/Liter of Baking Soda to it. When making a green puree add 1g/kg of Baking Soda while blending. Etc…
Alright, so those are the big three. I promise you if you keep literally just those three rules in mind then you’re 90% of the way to having the most vibrant green veggies, purees and leafy greens of your life. However, I’d be remiss if I didn’t cover the final two. Metal Ions, it sounds kind of scary at first but trust me it’s not. Calcium, Sodium, Potassium, Magnesium all of these are metals. The Emerald itself is a Metal Ion (Mg++). So then what’s the issue. Well the King who holds the Sceptre is a bit colorblind and sometimes can’t really tell the difference between his Emerald and a Sapphire or a Ruby. It’s sometimes even the case that if he sees a particularly well polished glimmering gemstone in his collection, he might swap it out, believing that he’d actually found a more dazzling Emerald to increase his grandeur. The rest of the court would play along of course, pitying the man and his blindness. The way this shows up in the kitchen is in the form of hard water. What actually defines hard water is how many dissolved ions there are in it. Usually Calcium but also Magnesium. Like I mentioned before, this is not a huge effect but it is there. Additionally, the harder your water, the longer it’ll take to cook your greens in it and if we remember our first rule then we already have a pretty good reason to use soft water in our cooking. This might also be yet another reason to steam rather than blanch, as these calcium ions don’t evaporate.
When adding water to your food, try to make it soft water, whether that be simply filtered or fully de-ionized. If you can add some additional Magnesium without affecting flavor, you might be able to better preserve your green color.
Alright, last one I promise. Photo-Oxidation is really something that only shows up as being a factor in my cooking over the course of days. This isn’t because the effect is weak but more because it only shows up in direct sunlight, which is not really all that common of a food storage space. If you do a lot of outdoor cooking in the sun then this is for you. When you think about it though, it makes a lot of sense that chlorophyll would have some sunlight and oxygen sensitivity. Photo-Oxidation isn’t just a chlorophyll thing or a food thing. It’s a very common chemical reaction that happens to different molecules and materials in the presence of specifically Oxygen and UV light that basically rips apart the molecule. In the analogy this would be like hardworking and beleaguered peasants being allowed in the presence of the sceptre wielding king and when the opulent decadence of the sceptre catches the morning light at just the right angle, it fills the peasant with a vengeful fury powerful enough to overcome his reason and makes him lunge for the sceptre, first ripping out the Emerald and then breaking the sceptre into pieces before lunging at the nearest member of the royal court and having to be tackled to the ground. The rule here is simple.
Store your greens in an airtight(preferably vacuum sealed) environment out of sunlight.