One packet says sand-roasted; the one beside it says far-infrared. It is tempting to ask which way each tea was roasted, but the two are not necessarily different methods. Some sand roasting runs on far-infrared heat from warmed stones.
What follows unpicks the names into three layers, then looks at the work of the machines: warm stones, a turning drum, air blown upward.
Words on three layers
In the roasting room the machines turn with a low hum. Sand roasting, direct fire and far-infrared heat are not words on the same layer.
In a kitchen, the shape of a pan and the burner under it are thought of separately. A roaster's description likewise mixes the vessel that holds the tea, the way heat is delivered, and the contact with the flame. A rotating drum names the vessel and its motion, far-infrared names the delivery of heat, and direct fire names contact with the flame. So they are not three options to pick one from, and some machines use more than one.
The name alone does not settle the taste. The record supports only a way to unpick the words. After the layers comes sand roasting, which passes heat from warmed stones.
The soft heat of warmed stones
In the roasting pan, warmed stones give a faint rattle. Sand roasting is a way of passing heat through stone.
One tea shop presents sand roasting as a traditional method using far-infrared heat from warmed stones. Its aim is to fire the tea evenly and bring out sweetness without scorching. Another shop, firing blended tea again at a higher heat, uses both a sand roaster and an infrared firing machine. One shop does not always mean one method.
Every account quoted is one the maker published itself. Their temperatures and times are not set out on common terms, and the same method name yields different finishes from shop to shop. That is as far as the record goes. After the stones comes the inside of a turning drum.