Hello, I’m Andrea Castillo and this is Seasonal, a newsletter that connects you to the Bay Area food system, one fruit and vegetable at a time. Each post highlights the most interesting aspects of one seasonal fruit or vegetable grown and harvested around the Bay Area. Find me on Instagram at @seasonalbayarea or e-mail me at firstname.lastname@example.org to share your feedback and suggestions, I’d love to hear from you. If you’d like to unsubscribe, click the link at the bottom of this post.
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This week we nerd out on makrut limes (leaves available year-round, fruit available November-January).
the essence of a dish
“As American as apple pie” is an idiom that describes something quintessentially American, like baseball or, well, apple pie. Funny thing is, neither apples nor pie originated in the United States. “As Thai as makrut lime” would be a more fitting idiom for something undeniably Thai, especially because makrut limes actually originated in Southeast Asia. Without makrut lime, red, green, and panang curries and tom yam and tom kah gai soups wouldn’t exist. Sure, you could make those dishes without makrut lime, but they would lose their Thai essence and transform into an underwhelming curry or soup—just as you’d end up with plain toast if you make a grilled cheese sandwich without cheese.
The Thainess of makrut lime was immediately evident by how few mentions it gets in non-Thai cookbooks. After scouring The Food of Morocco, The Food Lab, Yogurt, El Mundo Gastronómico, and Salt Fat Acid Heat for recipes that use makrut limes, I came up empty-handed. I managed to find three recipes that called for makrut lime leaves in 101 Easy Asian Recipes and knew I’d find some in an Ottolenghi book—he’s a fan of cooking with makrut leaves—except I don’t own any yet. But after dusting off a copy of Gap’s Culinary Art School and Wanphen Heymann-Sukphan’s The Foods of Thailand, every other page had a recipe that included makrut lime leaves or peel.
One thing to note about this citrus is that it has many names such as Thai lime, Indonesian lime, caffre lime, and the derogatory kaffir, which is a more common name than makrut. This derogatory word is one of the most offensive racial slurs in South Africa: a woman was sentenced to jail for racist speech and verbal assault when she called black police officers the k-word dozens of times. The word makrut originates from the Thai language ( มะกรูด (má-grùut) ) and is an inoffensive, suitable name for this fruit.
leaves and peel
Unlike other citrus fruits like lemons, oranges, and grapefruit, makrut lime juice is rarely consumed: it’s intense and bitter. The most sought after parts of the makrut lime are the unique two-in-one leaves on the tree, followed by the bumpy peel that encases the juicy pulp. In Thai cuisine, whole makrut lime leaves, which are rich in oils, add an incredible taste to soups. Makrut leaf oils teem with rich, rare, mirrored citronellal compounds that release powerful and unusually bright and clean aromas. Makrut leaves are not eaten whole in soups, but in prawn salads or ho mok (soufflé) fish they are part of the dish and eaten as millimeter-thin slices that deliver explosions of flavor in every bite. The peel from the makrut lime is also eaten, but as one of many ingredients that is pounded into the foundational pastes for green, red, or panang curries.
Thai curries, soups, and salads reflect the natural availability of native foods in Southeast Asia. With its origins in Southeast Asia, the ubiquitous makrut lime tree is an undeniable underpinning for Thai culinary and cultural identity. You can’t take makrut out of Thai cuisine, but it’s challenging to take fresh makrut out of Southeast Asia— during the 1970s and 1980s, as Thais migrated across the Pacific Ocean, Thai cooks in the United States had very little access to fresh makrut leaves and other essential fresh ingredients.
growing demand and diminishing supply
During those decades, the short supply was likely a result of growing demand and the novelty of fresh food ingredients Americans did not use or grow. So for a while, cooks had no choice but to rely on imported Southeast Asian frozen or canned vegetables to prepare meals that Thai grandmas would disapprove of.
The Thai immigrant community kept growing, particularly in Los Angeles, and as it fueled a stronger demand for fresh Thai ingredients, makrut lime leaves entered the market—whether imported or smuggled. In 1995, however, a sudden makrut shortage shocked the nascent market. At that time, California banned makrut lime imports, and with few makrut lime growers in the state, seasoning Thai curries and tom yum soups that grandmas would be proud of amounted to an almost impossible mission once again. But this time, supply shortages weren’t tied to novelty as they were in the 70s and 80s. This time, shortages resulted from our interconnected global trade system, which altered nature’s natural defenses against disease and paved an unintentional warpath straight to the heart of America’s citrus industry.
The disease, known as citrus canker, is a bacteria that originated in Southeast Asia or India. It thrives in warm, moist conditions, and weakens citrus trees, forcing them to drop their leaves and premature fruit. Citrus canker has no cure and hops from victim to victim on any vessel: a pair of contaminated shears, rain, and even wind. Citrus canker doesn’t care about customs regulations and will free-ride with no shame whenever the opportunity arises.
Citrus canker showed up in the United States for the first time in 1910, hitching a ride into Florida on an infected seedling imported from Japan. Without a cure, there was no option but to kill every infected tree to contain the disease. So, from 1910 to 1931, Floridians took on the herculean effort to destroy 3.3 million citrus trees to eradicate citrus canker. The 21 year-long effort worked and Florida’s citrus groves grew in relative peace until the disease came back with a vengeance. In 1995, citrus canker spread from a residential area in Miami like wildfire and invaded Florida’s citrus groves again. Two million dead trees and a decade later, Florida had no choice but to give up: in 2006 the state declared it would be impossible to eradicate the disease.
The 1995 Florida outbreak rang alarm bells in California, where officials clamped down on citrus imports from other states and countries. But homesick immigrants and fans of Southeast Asian cuisine drove demand for makrut lime leaves, which led to makrut lime leaf smuggling and prompted a stricter crackdown—hence the shortage of makrut limes back then. Fearing a citrus black market as a reaction to increased regulation, the University of California Lindcove Research and Extension Center grew and distributed 300 clean makrut lime trees to commercial growers, enabling a safe local makrut lime leaf market to grow.
With more makrut lime trees growing in California, supply steadied and grocers sourced from local growers like Jacobs Farm. Luckily, California built a strong enough regulatory barricade to keep citrus canker away and extended legal access to precious makrut leaves. Cooks from the established Thai diaspora in California were finally able to infuse their dishes with a longed-for taste of home.
Today, even though makrut lime leaves are not as common as staple California items like avocados, they are relatively easy to find at Bay Area Asian markets, grocery stores, or at garden supply businesses. California growers and nurseries like Four Winds Growers, Pearson Ranch, and Berkeley Hort all sell makrut lime trees for those who want to have a perennial supply of makrut leaves in their backyard. Considering fresh makrut leaves can cost as much $120 per pound, the $30 tree that doesn’t mind growing in a container is not a bad deal.
For all things regarding growing backyard makrut lime trees in the Bay Area, Kasma Loha-unchit, an Oakland resident, is the leading local authority. In her thorough, 20-part blog post about makrut limes, she explains that California, where 60% of households grow a citrus tree, does not resemble the hot, humid, rainy environment the tropical makrut lime tree is most happy in. But west coast weather is nice enough and California makrut lime trees have acclimatized with a little extra help. It’s not too difficult to grow makrut lime seedlings from seed, but you’d need to wait a couple of years to harvest the leaves and around seven years to enjoy the fruit. To speed up the process, many makrut lime trees are grafted to the lower part of an already established tree, which is known as the rootstock. As an added bonus, citrus rootstocks that already enjoy the cooler, drier California weather share their tolerance with the grafted tropical makrut lime branch. Once the branch and rootstock fuse into an established makrut lime tree, the hearty rootstock helps the tree thrive and bear fruit.
A rootstock that tolerates cold and dry climates can only go so far, however, and commercial makrut lime tree groves are most likely to succeed in warmer climates where other citrus thrives like Texas, Florida, Arizona, and California. While climate factors limit the supply of makrut limes and leaves to specific areas in the United States, demand for fresh makrut leaves has grown throughout the country because of the rise in popularity of Thai and Southeast Asian cuisine. Thai food made with fresh ingredients has won the hearts of many American eaters, and after branching out of Thai Town in Los Angeles and other major cities, it is also popular in smaller towns like Bend, Oregon. Restaurant chefs and home cooks throughout the United States all want to get their hands on fresh makrut leaves when preparing Thai dishes. With this added pressure from higher demand, the ripples from disruptions to makrut lime supply are now felt by many, especially in colder states that rely on imports from warmer states.
the bacterium strikes back
In 2008 and 2010 in New York City and Boston, for example, fans of makrut lime noticed that their reliable local markets were out of makrut leaves, struggled to find them, or, as supply and demand economics predicts, ended up paying a high price if they succeeded in their treasure hunt.
Why? Disease. Again. Another epidemic hit citrus growers, and this time it spread far and wide from Florida, to Texas, to California. Bostonites and New Yorkers had difficulty finding makrut lime leaves because one of the few makrut-growing states, Florida, was the first target of a bacteria attack worse than citrus canker. State officials mandated quarantines and restricted imports, which squeezed makrut lime supply once again.
The disease, known as huanglongbing (HLB), is now a full-blown epidemic and one of the most destructive citrus diseases in the world, decimating citrus trees in Asia, Africa, the Middle East, and the Americas. When HLB attacks, citrus trees grow bitter, inedible fruit. It also spreads fast: in a little over a decade, HLB reduced Florida’s production of oranges and grapefruits by 75% and 85% respectively. This disease is so devastating and scary to citrus growers in California, a state that grows 80% of the citrus in the United States, that any potential symptom or sighting of the small insect that can carry HLB prompts panic. On their citrus page, for example, the Monterey Bay Nursery in Watsonville, California implores its customers to take thorough precautions in their public service announcement:
“There are a few really nasty diseases out there, and one of them has by now just about completely eradicated the famous Florida citrus industry. Therefore: you will ALWAYS clean all the gum, resin and crud off your clippers using water and a nice chunk of pumice or perlite, then sterilize with 2% bleach or its approximate equivalent (Clorox Cleanup, etc.) for at least 2 seconds before you cut any citrus tree (or banana, or actually any other plant that you really value, including hardy fruit trees). You WILL learn what Asian Citrus Psyllid looks like, and also the symptoms of Huanglongbing (HLB). You WILL contact your county ag inspector if you find them.
I now command you to say "YES MASTER! I HEAR AND OBEY!"”
Monterey Bay Nursery’s concern is spot on. A growing worry for citrus researchers is how humans increase the risk of spreading HLB. For now, natural barriers including cooler weather in Central California help confine the disease to Southern California. HLB can hack those barriers without much effort though. All it needs is human help to transport infected fruit, leaves, or tools from the quarantined areas and it will wreak chaos in disease-free zones.
But why would we help spread this terrible disease? We wouldn’t do it on purpose. We’d provide assistance without meaning to. If our cravings or homesickness drive a strong desire for a forbidden fruit (or leaves), it’s not impossible for that item to find its way into the United States—according to a CIA-esque database of smuggled produce, makrut limes have made it on the illegal import list (to my surprise, the most smuggled citrus is the Colombian sweet lime when it’s out of season in the United States). Even with tight domestic controls, perhaps we will be a little careless and half-ass equipment sterilization or have no knowledge of what the symptoms look like and move a diseased fruit, branch, or leaf anyway. Whichever way, if HLB ends up in Central and Northern California, human assistance will be the likely reason. Unless we figure out a cure first.
From sniffing dogs, to AI, traps, and drones, researchers are working hard to fight against HLB. Scientists are also leveraging nature to find a cure and with genes immune to HLB disease, Australian finger limes may be able to offer the secret weapon we need. To figure out whether Australian finger lime immunity works with other citrus, several field trials need to take place in Florida. But it’s not safe for humans to conduct those tests at the moment. As we deal with our own human epidemic, those tests will have to wait until we reduce the spread of COVID-19 or build up enough immunity with effective vaccines.
while supplies last
For the time being, citrus quarantines and regulations will have different impacts on makrut lime leaf availability. In the Bay Area, supply remains somewhat reliable and if you’re in the mood for cooking Thai or Ottolenghi-inspired dishes, you should be able to. This Temple of Thai tom yam soup is not super elaborate to make if you can get your hands on all the ingredients (the recipe in my Gap’s cookbook didn’t call for tamarind paste and the soup tasted great anyway). Green curry is another classic dish that calls for fresh makrut leaves, though it is a bit more elaborate—especially if you make the green curry paste from scratch with makrut lime zest. Yotam Ottolenghi incorporates makrut leaves in many of his recipes and I was lucky enough to taste his hasselback beet with makrut leaf butter when my husband’s cousin made it for us. It is fantastic. After all that cooking, if you have leftover lemongrass and makrut leaves, a simple herbal tea made with both is delicious after lunch or dinner. And if you still have makrut leaves left after that, freeze them! They keep well frozen.
The hyper-connected food system we’ve designed enables us to get anything we want whenever we want it: we fly in fresh makrut leaves from 8,217 miles away or grow tropical makrut lime trees in our Bay Area backyards. This hyperconnectivity is impressive and beautiful: we can find soothing tastes of home almost anywhere we land—and share that joy with others. As Thai and other Southeast Asian dishes conquer the American palate, we continue to drive demand for the powerful fragrant makrut lime oils that delight our tastebuds. Unfortunately, the beautiful intricacy of our food system can turn into a vector for destruction in the blink of an eye. When store shelves and online carts lack the indispensable makrut leaf all of a sudden, temptation will kick in to ship leaves during quarantine or bring them in from other countries—intentionally or unintentionally. With or without intent, moving potentially infected plants during a citrus epidemic in our interconnected food system not only stands in the way of the Thainess of Thai cuisine in America, it also poses grave risks to the millions of citrus fruit we work so hard to grow. It is up to us to take every precaution to ensure we do not wipe out our citrus groves.
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Andrea Castillo is a food nerd who always wants to know the what’s, how’s, when’s, and why’s of the food she eats.