Sweet basil in winter: bunches, chilling and the downy mildew problem

Sweet basil is the one herb a kitchen cannot fake. Pesto, a Margherita, a caprese plate: each depends on the aroma of a fresh leaf, and that aroma is lost to cold faster than to time. King Quality Produce runs a winter sweet basil program, December through February, packed 60 bunches to a box, to cover the months when local basil is scarce. Here is what the Genovese type is, where winter basil comes from, how to receive and store it, and what USDA says is in the leaf.

What sweet basil is and what KQP packs

Sweet basil is Ocimum basilicum, and the Genovese type is the large-leaf, cupped-leaf Italian form bred for pesto and pizza. Purdue's 1985 production guide sorted commercial basil into French, American and camphor-scented Egyptian types, and noted that more than 50 Ocimum species and forms exist, which is why seed and flavor vary from lot to lot⁸. What ties sweet basils together is the oil: in a 2017 analysis of basil essential oils, the green O. basilicum variety studied was a linalool-rich chemotype, 68 percent linalool with about 20 percent methyl chavicol⁶, and linalool is the soft, floral note you smell when you tear a leaf.

KQP packs sweet basil in bunches, 60 bunches to a box. A bunch is a handful of stems cut above the lower leaf sets, which is how growers harvest so the plant regrows for the next cutting⁸. We sell sweet basil by the box in winter only; the rest of the year our basil business is opal and lemon basil, which we carry year-round.

Where and when it grows

Basil is a warm-weather crop. It grows best between 45 and 80°F, is killed by frost, and in warm climates gives three to five cuttings a year against about two in cool ones⁵. Commercial U.S. basil is grown mainly in Arizona, California, Florida, New Mexico and North Carolina, and Mexico is a large exporter to the United States; USDA does not track basil separately from the broader herb category⁵.

That geography is the reason for our winter program. From December through February, California field basil is thin or gone, and the basil coming into Los Angeles is from desert and Mexican growers who can keep cutting through the cool months. KQP brings winter basil in daily from growers in Mexico, the Southwest and California.

The other reason supply swings is disease. Basil downy mildew, caused by Peronospora belbahrii, was first confirmed in the United States in 2007 in Florida and was found throughout the Northeast by the following year; it spreads mainly on wind-borne spores and can infect a planting within hours of wet weather, with symptoms showing 5 to 10 days later⁴. Sweet basil is the most susceptible type, which is why breeders have released less-susceptible varieties such as Amazel, Prospera Active and the Rutgers DMR series (Devotion, Obsession, Passion and Thunderstruck)⁴. When a field goes down to mildew, bunches get short and prices move.

How to buy sweet basil: bunches, boxes and receiving

Sweet basil comes 60 bunches to a box, and a box is the unit we quote. Growers harvest before bloom in the cool, dry part of the day, and bunches are kept loose so air can move through them³. On receiving, UC Davis's quality indices for culinary herbs are the checklist: freshness, uniform size, form and color, no yellowed or damaged leaves, no decay, insect damage or wilting, and a strong characteristic aroma². Aroma is the check buyers skip; smell every box.

Two defects are specific to basil. The first is chilling injury, which shows as blackened leaves, stem discoloration and loss of aroma³, or in UC Davis's description as browning of the leaves and growing tip, bronzing of the veins and loss of gloss². If a truck ran at 34°F for the lettuce, the basil on the same pallet will show it quickly. The second is downy mildew, which starts as a yellowing bounded by the leaf veins that looks like a nutrient deficiency, then shows a purple-gray fuzz on the underside of the leaf⁴. Reject either on sight.

• Smell the box before you count it
• Leaves glossy and even green, no black or bronze patches
• Stems firm, not slimy or discolored
• No yellowing bounded by leaf veins, no gray fuzz underneath
• Bunches loose in the box, not packed tight and wet

Storage and shelf life

Almost every herb wants to be cold; basil does not. UC Davis recommends 32°F for most fresh herbs, with about three weeks of life at 32°F and two weeks at 41°F, but states that basil and shiso are chilling sensitive and should be stored above 50°F, at relative humidity above 95 percent². Rutgers puts the optimum at 55°F with 90 to 95 percent humidity, citing UC Davis research in which basil held at 50 to 68°F for ten days kept markedly better visual quality than basil at 32°F³. Expect one to two weeks of shelf life, depending on water loss².

In practice, basil lives in the warmest cooler you have, or in a cool prep room, never in the 34°F walk-in with the greens. Keep bunches loose, stand stems in water or cover them loosely to slow moisture loss, and never let basil touch ice³. Basil is minimally affected by ethylene, so proximity to tomatoes is not the problem it is for parsley or mint; cold is². Chilling also costs flavor: storage at chilling temperatures greatly reduces basil's aroma quality, and aroma declines in storage even when the herb is handled well², so buy what you use in a few days.

Nutrition by the numbers

USDA FoodData Central's entry for fresh basil reports, per 100 g: 23 calories, 92.1 g water, 3.15 g protein, 2.65 g carbohydrate, 1.6 g fiber, 177 mg calcium, 3.17 mg iron, 64 mg magnesium, 295 mg potassium, 1.15 mg manganese, 18 mg vitamin C, 68 µg folate, 264 µg vitamin A (RAE), 3,142 µg beta-carotene, 5,650 µg lutein plus zeaxanthin and 414.8 µg vitamin K¹.

Against FDA's Daily Values of 120 µg for vitamin K, 2.3 mg for manganese, 900 µg RAE for vitamin A and 90 mg for vitamin C⁷, 100 g of fresh basil carries more than three times a day's vitamin K, about half a day's manganese, 29 percent of the vitamin A and 20 percent of the vitamin C. No one eats 100 g of basil at a sitting, but per gram the leaf is rich in vitamin K and carotenoids. Those are measurements, not health claims, and USDA's entry is generic fresh basil rather than a specific cultivar¹.

In the kitchen: how Los Angeles uses sweet basil

Pizzerias and Italian kitchens are the volume buyers: whole leaves on a Margherita after it leaves the oven, torn into caprese, blended into pesto by the quart. Sandwich shops and delis layer it with tomato and mozzarella. Markets sell bunches to home cooks, where the bunch often goes straight into a cold home refrigerator.

Tear rather than chop where you can, add it at the end of cooking, and make pesto in small batches with the surface covered in oil. Wash only what you will use and dry it before it goes back on the rack; wet basil in a cold box blackens fast. On a market floor, keep bunches out of the misted case and off the ice.

Our winter sweet basil runs December through February, and bunch size and count move with the weather in the growing regions. Call the office at (213) 627-7181 or email office@kingqualityproduce.com for this week's counts.