Why we don’t dry in the sun

Sun drying is cheaper, it needs no electricity, and it is how most powder sold in India is made. It is also why most of it tastes of very little.

If you have ever bought moringa powder that arrived the colour of dry hay, or amla powder that was grey-brown instead of pale green, you have met a sun-dried batch. The fault is almost never the plant. It is the four or five days the plant spent lying on a tray in the open.
We dry everything in a closed, temperature-controlled chamber instead. It costs more, it needs power, and it is the single decision that most affects what ends up in the pouch. Here is what actually changes.

Chlorophyll breaks down in ultraviolet light. That is not a subtle chemical footnote — it is the reason a green leaf left on a windowsill turns yellow in a week. Spread moringa or mint on an open tray in Indian sun and the same thing happens over three days, unevenly, because the leaves on top shade the ones below.
Beetroot has the same problem with a different pigment. Its red comes from betalain, which is heat-sensitive and light-sensitive both. Sun-dried beetroot powder tends towards a dull brick colour rather than deep red, and once it has gone there is no way back.
Drying in the dark holds the pigment. That matters commercially too, because a powder that keeps its colour is a powder nobody needs to add colour to.

Everything you smell in mint is volatile oil, and volatile means exactly what it sounds like: it evaporates. A tray of pudina in 40°C sun for two days loses most of it into the air. What is left looks like dried mint and smells like paper.
Controlled drying runs cooler and faster. The pouch still smells of mint when you open it, which is the only test that matters and the one most dried mint fails. Same principle for ginger and green chilli, both of which carry their character in compounds that do not survive slow heat.

This one you cannot see, which is why it is the easiest to get away with. Vitamin C degrades with heat, with light and with time. Amla is bought almost entirely for its vitamin C, and amla dried slowly in the open loses a great deal of it before it ever reaches a mill.
The powder still looks like amla. It is still sour, because the acids that make it sour are more robust than the vitamin. A customer has no way of knowing, and that is precisely the problem with the practice.

An open tray is open to everything. Road dust, insects, birds, and whatever is in the air on a given afternoon. In a monsoon month there is a second problem: the tray comes in dry at six in the evening and picks moisture back up overnight, which is how a batch ends up faintly musty or fermented at the edges.
Dates are the worst case, because they are close to two-thirds sugar. Sun-drying a high-sugar fruit in the open is the most hygienically risky thing you can do with it, and it is done routinely.
A closed chamber removes the question. Nothing lands on the product, and the moisture level at the end of the cycle is the moisture level you set.

Sun drying depends on the weather, and the weather is different every week. A batch dried in dry February heat is not the same product as a batch dried in humid July, even from the same field and the same variety. The colour differs, the moisture differs, the taste differs.
For a home cook that is genuinely annoying. You work out that half a teaspoon is right, and then the next pouch needs a full one. Controlled drying means the pouch you buy in March behaves like the one you bought in November — which sounds like a small thing and is, in practice, the whole point of buying a powder instead of the fresh vegetable.

None of this is a secret in the industry. Every producer knows sun drying costs colour, aroma and nutrition; it is chosen because it is cheap and because most customers cannot tell. We would rather charge a little more and have the pouch smell like the thing on the label.
That is the entire argument, and it is testable. Open one and see.