Nilgiri Frost Tea, and How Tea Leaves Respond to the Cold

Being frostbitten is generally a negative experience—for you and for many plants. Much research goes into how to best protect tea plants from frost, and in some regions of the world, such as the Caucasus, frost-tolerant genotypes have been developed. These genotypes allow plants to thrive in colder regions, which has two benefits: the plants can better tolerate extreme weather, and there are fewer pests in cold environments. 

But here we have Nilgiri Frost, a tea that capitalizes on having been touched by frost! What happens when a tea plant experiences frost, and when is it good vs when is it bad?

nilgiri frost leaves

Stress and Tea Production

Cold temperatures and frost stress the tea plant—and stress has long been part of tea production.

Shading plants from a few days to several weeks will force the plants to produce more chlorophyll and the amino acid L-theanine. The resulting tea will be brighter green (chlorophyll) and will have more umami due to the higher level of theanine. Gyokuro, kabusecha, and matcha are examples of such teas.

Allowing a certain level of damage by tea green leafhoppers results in the unique Oriental Beauty tea because the stressed plants fend off the insects by releasing specific volatile chemicals. Tea producers harvest these chemically changed leaves when they have just the right amount of damage to maximize the flavor profiles that we most enjoy. (Read more about this fascinating phenomenon at Tony Gebely, Tea Epicure.)

Takatomo Katagi of Katagi Koukaen in Japan plucks frozen tea leaves and manipulates them by hand to produce his unique (and extremely small batch) frozen black tea.

The Nilgiri Hills (Blue Mountain) are located in southern India, and at 3200–8200 feet in elevation, are ideal for growing and harvesting tea—especially oolong and black tea—year-round. For Nilgiri Frost tea, leaves are plucked during winter, at night or very early in the morning, when frost has hit and the leaves are lightly frozen. The leaves thaw as they continue to wither during production.

It’s clear why tea produced from stressed tea plants is costly, only small quantities are available, and the mastery of the producer is critical to the process.

nilgiri frost brewed lvs

How Cold and Frost Impact Tea Leaves

We all know that a tropical plant will droop and generally not recover from prolonged exposure to cold, yet may be fine with a light frost.

Tea growers may protect their plants from the cold, perhaps with fans or water sprinkling, because when a leaf freezes, the water inside that leaf freezes, breaking the cell walls. Of course tea production is about breaking those cell walls to allow oxygenation of the leaf, but in a controlled fashion. When the leaf freezes, its cells break and lose their contents, and the leaf dies.

If the leaf is only exposed to frost and isn’t fully frozen, the frost affects the leaf’s exterior first, which protects the leaf’s contents (and those cell walls).

A 2020 study by L. Samarina et al. looked at how different tea (Camellia sinensis) cultivars—some cold-tolerant and some cold-sensitive—respond to cold temperatures and to frost. 

The researchers, and those of earlier foundational studies, found that:

  • Tea plants respond differently to cold vs to frost.
  • Thousands of genes are involved in the plants’ response; both cultivars showed significant changes in gene expression when exposed to both cold and frost.
  • Both the tolerant and the sensitive cultivars had elevated water-soluble protein levels (3–4x higher) when exposed to cold and frost; this helps the plants acclimate to the environmental change.
  • Both cultivars had higher magnesium, potassium, and calcium levels when exposed to cold and frost; this affects the enzymes and metabolism of cells, helping the plant tolerate frost.
  • When exposed to cold, 6 amino acids increased in levels in the tolerant cultivar, whereas only 2 were increased in the sensitive cultivar. When exposed to frost, 5 increased in the tolerant, but 4 increased in the sensitive. These amino acids are critical to the plant’s response to cold.
  • In the sensitive cultivar, the pH changed from acid to base when exposed to frost, due to osmotic stress.

nilgiri frost brew

Making Tea from Frostbitten Leaves

To intentionally produce tea from leaves hit by frost, the leaves must be plucked while still frost-nipped and then allowed to thaw as part of the production process. (This is similar to ice wine, where the frozen grapes are picked during the night and kept frozen until they are ready to be processed.)

From Samarina et al.’s research, we know that these leaves are different from those that have not been touched by frost or cold. The leaves have made changes as they’ve tried to prevent damage and have compensated for the environmental conditions. There are genetic changes, along with changes in levels of proteins, amino acids, acidity, and minerals. All of these alter the properties of the leaf and subsequently what we taste. Like I quoted Phil Attee previously, it’s art plus science, with the art being “What flavor profile do you want?” and the science “How do you get that?”

For frost tea, producers know what flavor profile they are aiming for, and they use their knowledge of biology and chemistry to attain that.

Nilgari Frost Tea

So is the tea itself worth all the work?

Well, there are many fine teas in the world, and I would put this one among them. Whether it’s worth the price is an individual decision, but it is a lovely tea!

In my sample from TeaHaus (currently available as part of a monthly brew tea sampler), the dry leaves range from oxidized reddish chocolate brown to nearly black, sprinkled with small pieces of lightly oxidized leaves that have retained their light green color. After brewing, you can see how some leaf edges are muted burnt sienna or yellow orange in color, and the leaves are shades of green to yellowish- and brownish-green.

The liquor, which looks light yellow-brown in a shallow cup, has a sweet aroma, with floral and fruity notes.

I love how smooth this tea is. To me, it’s first of all sweet, but with fruity and floral notes. It doesn’t linger very long on the palate, but the finish is soft and pleasant.

A second brew yields a slightly browner cup, and far less of the sweetness of the first brew. With a bit of a sharp note, it’s still pleasant and very enjoyable, though with a slightly astringent finish.

brew and leaves alt

Sources:

–Samarina L. S., et al., “Physiological, biochemical and genetic responses of Caucasian tea . . . genotypes under cold and frost stress,” Plant Biology, 8/28/2020.

–Scott, E., “Oriental Beauty and other bug-bitten teas,” Tony Gebely, Tea Epicure, accessed 8/4/21.

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