October 14, 2020

Sourpuss? Sour Plus!

Key lime (Citrus aurantifolia) hanging in tree
We began planting our mini food forest at the turn of the 21st century. As we embarked on this adventure, we had one key lime tree, probably planted in 1965 when the house was built. This gnarled old beauty, even at about fifty-five years of age, continues to produce fruit year after year. The act of planting a fruit tree demonstrates a certain confidence in the future. We enjoy it in our time and know that we will most likely pass it on to those who come after us. Our key lime tree did more than hold out the promise of key limes. It also showed us that the contrived pile of sand and shell we were living on could also provide us some food. 

Key lime trees naturalized in the Florida Keys, perhaps centuries ago.

The far traveled genes of this singular citrus are believed to have originated in Asia. Along the way, it acquired new names, for example West Indies lime and Mexican lime. Groves of key lime trees were intentionally planted in the Florida Keys at around the turn of the 20th century, at which point it was rebranded as the key lime. Their commercial success in Florida didn't last long. The 1926 Miami Hurricane laid waste to those early key lime groves. Growers replaced them with the hardier, thornless Persian lime. Subsequent land development replaced many remaining key lime trees with residential subdivisions for other sorts of transplants. Today, backyard key lime trees like mine are all that is left of key lime production in the United States. 

In my yard, we know key limes are ready for harvest when they have fallen to the ground. Picking key limes from the tree can be somewhat hazardous. The trees have spines. They are large and nasty when the trees and branches are young. They are smaller, but still potentially painful, as the trees and branches age. Fallen key limes are usually ripe, yellow, and juicy; however, once off the tree, key limes will only ripen slightly, if at all. When unripe and green, key limes are significantly harder to squeeze, hold significantly less juice, and have significantly less flavor. By collecting key limes from the ground, I harvest them when they are as juicy as they will ever be. Once they are off the tree, they start to dry up. In my experience, they dry out faster in the refrigerator, so I leave them out on the counter. 

A young key lime branch with long sharp spines

It seems like a bit of magic to me, but the juice from a ripe and very sour key lime brightens and enhances other flavors. Key lime underlines and highlights the flavor of avocados and papaya, but my favorite combination is cranberry and key lime. It is counterintuitive, but adding a splash of key lime juice to cranberry juice reduces its sharp edge and adds a bright note. My sweetheart buys fresh cranberries and makes a key lime cranberry sauce from scratch. It is always a hit at Thanksgiving, and it is a key component of gourmet sandwiches throughout the year. When my sweetheart is in the mood for a mouth-waking treat, he spreads his key lime cranberry sauce on his morning toast.

Key lime pie ingredients. 

By far, the most popular use for key limes is in key lime pie. Aside from delighting in its taste, about the only thing everyone agrees on is that a key lime pie is made with key lime juice. Many would also agree that it is best to use fresh juice. Bottled key lime juice made from concentrate and treated with preservatives lacks the high sour notes and often has metallic undertones. Beyond that, there is pronounced disagreement. 

One question that has plagued connoisseurs of key lime pie for decades is whether the key lime filling, if made properly, should be yellow or green. The answer depends on another key question - should a ripe key lime be yellow or green? Most people don't know the answer to this second question. The answer may surprise you. Most fruits start out green and then change color as they ripen. Green bananas turn yellow. Green papayas turn orange. Green tomatoes turn red. Green blueberries turn blue. Like most fruits, key limes are green when unripe. As they ripen, they turn yellow; however, the color of the pie is dependent on the actual ingredients.  Due to the variety of recipes, the color of key lime pies vary. If the ingredients include egg yolks, expect a yellow color. If the ingredients include green food coloring, expect an unnatural, bright green color and feel free to walk away. 

My sweetheart's key lime pie is neither green nor yellow, but it is delicious

Key limes are more acidic than lemons. Much like adding vinegar to a salad or red wine to a soup, the acidity in key lime juice adds a twang to whatever you might be cooking. Substitute key lime juice for vinegar in vinaigrette and you get a tasty salad dressing with a more floral aroma. Recipes for salsa generally include vinegar or lime juice. My vinegar tree has never produced anything, but I do have wonderfully productive key lime trees, so I use key lime juice in mango salsa, as follows.  

Mango salsa ingredients
Combine the following - 
Vegetable or Fruit or some combination
(tomato, corn, mango, ...) 
(habanero, jalapeƱo, Thai, ...)
Fresh herbs
(mint, basil, cilantro, ...)
Key lime juice

You can dice the ingredients into small pieces or you can throw them in a blender. You can get fancy and grill or caramelize some of the ingredients. I put freshly made salsa in the refrigerator for a few hours. As it sits, the fresh flavors blend together, limned by the bright tartness of the key lime juice. 

Mango salsa with corn

The acidity of key lime juice initiates chemical activity in some recipes. Although I have no personal experience with ceviche, I understand that the key lime juice in a ceviche marinade changes the texture of seafood. Protein is made up of chains of amino acids. When the proteins in the seafood are marinated in the acidic key lime juice, these chains rearrange themselves. In the case of ceviche, the seafood firms up, as if it had been cooked. I was curious as to what goes into a ceviche recipe, so I read through a few of them. My half-baked verdict is that ceviche is basically seafood marinated in a key lime salsa. I will continue to skip the seafood and enjoy the salsa. 

Artistic rendition of 
key lime juice causing rearrangement of seafood amino acid chains

Recently, I experimented with tzatziki, a creamy Greek yogurt sauce/dip usually made with cucumbers and fresh garlic. I played with a variety of strong herbs and added a large helping of Surinam purslane. Thanks to Julie C for the suggestion. I made a version with a hefty dose of key lime juice to give it a stronger flavor along with some hibiscus flowers to give it a bit of color. I recommend it.

Key lime juice and spent hibiscus flowers
are the experimental ingredients in this tzatziki-to-be. 

Key limes are highly esteemed by bartending professionals. Unsurprisingly, what they are valued for varies from bartender to bartender. Some find the size of the fruit makes for a perfect garnish on a glass. Their special sourness perks up cocktails - key lime margaritas, key lime Mai Tais, and key lime daiquiris. When it comes to the Pisco Sour, key limes are said to have been the traditional Peruvian souring element. As a non-bartending teetotaler, I favor what I call a key lime fizz - homemade soda made from key lime juice, simple syrup, and carbonated water. Add some unsweetened cranberry juice, if you are so inclined. I like getting creative with the blender or juicer making thickened drinks, such as watermelon/key-lime/mint juice or orange/key-lime/carrot juice. 

Key limes at varying degrees of ripeness

Before you juice your key limes, if they have been in the refrigerator, let them come to room temperature. Some people microwave them for 15 seconds to warm them a bit more. Once warm, you can roll them on a hard surface to release more juice. Cut them in half across their midline. If you are only squeezing a couple of key limes, you can juice them by squeezing between your fingers. As you squeeze out the juice, run it through a strainer to remove the seeds. If you have more than a handful, you may want to use a tool. There are manual juice squeezers that look very much like a garlic press. I will go a step further and suggest that you might be able to use a garlic press for very small key limes. Let me know if it works. There are also electric-assist citrus juicers with attachments for smaller fruit. For a large quantity of fruit, this is a nice option. Once done, you'll realize that due to the skins, pulp, and seeds, your juice yield is far less than you anticipated. Part of juicing key limes includes complaining about how tedious the whole process is. If you decide to zest your key limes, be ready for even more complaining. You might be able to avoid the complaining stage, if you keep your mind focused on the health benefits of key limes, especially Vitamin C and antioxidants. 

I'd like to highlight one easy storage method for key lime juice. After juicing your key limes, pour the key lime juice into ice cube trays and freeze them. It only takes a few cubes to make a key lime pie. One cube can supply all the juice you need for two glasses of key lime fizz (soda). When I first froze key lime juice, I saved these cubes for months. Much to my dismay, they had shrunk to about 10% of their original height, when I went to use them. The rest had evaporated in the freezer. Since then, I make sure to remove the cubes from the tray and put them in a zip lock bag for long-term freezer storage.

Citrus greening (Huanglongbing) causes asymmetrical blotchy mottling of leaves

A key lime tree requires little care. First and foremost, they need good drainage, sunshine, and frost-free temperatures. The greatest threat to citrus trees where I live is citrus greening. This disease arrived in Florida in 2005, and has since decimated most citrus trees around the state. In my experience, key lime is relatively immune. Our oranges, calamondins, and tangelolo all eventually succumbed to citrus greening. Our key limes appear to be infected, but they continue to produce. In order to support our infected trees, I spray micronutrients on the leaves. Over a span of many years, a key lime branch produces smaller and smaller fruit. Since larger fruit makes for easier juicing, I have a strong preference for larger fruit. Consequently, every few years I will prune an older branch and let a younger one take its place. This seems to rejuvenate the tree and increase the fruit size. 

Some key lime history from David Sloan in the Keys Weekly:
The Ultimate Keys Condiment "Old Sour", April 11, 2019.
The Key Lime Massacre at Indian Key?, May 10, 2019. 
The History of Green Key Lime Pie July 19, 2019.
The Rise & Fall of Commercial Key Lime Crops, September 18, 2019.
Once and for All - Key Lime Pie's New York City Origin Story Disproved, October 4, 2019.


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