SMEG KLF04BLEU | Electric kettle with temperature control 50's Style | 1.7L | Colour: black

Why brewing temperature matters — the science of tea and coffee extraction at different temperatures

The temperature of water used for brewing tea or coffee is one of the most significant variables determining the taste of the final beverage — the difference between water at 70°C and water at 100°C in the same cup of green tea produces dramatically different results, and understanding why is the core rationale for the KLF04BLEU's temperature control feature. Tea leaves contain three primary classes of flavour compounds: catechins (polyphenols that produce bitterness and astringency), amino acids (primarily L-theanine, producing umami and sweetness), and volatile aromatic compounds (producing the characteristic floral, grassy, or fruity notes of different tea varieties). These compounds have different solubility profiles — they dissolve from the leaf matrix into water at different rates depending on temperature. At high water temperatures (90–100°C), catechins dissolve rapidly and in large quantities — producing a strongly bitter, astringent cup. L-theanine and delicate aromatics are also extracted rapidly but may be overwhelmed by the catechin bitterness. At moderate temperatures (70–80°C for green tea), catechin extraction is slower and more controlled — the resulting cup has lower bitterness, higher perceived sweetness (because L-theanine is now proportionally more dominant), and more delicate floral or vegetal aromatics that would be volatilised or masked at higher temperatures. This is why high-grade Japanese green teas (Gyokuro, ceremonial matcha) are brewed at 60–70°C: these teas are specifically shade-grown and high in L-theanine, and brewing at 100°C would make them unpleasantly bitter; the lower temperature produces a sweet, umami-forward cup that showcases the intended flavour profile. For coffee: coffee extraction follows similar principles. The Specialty Coffee Association recommends a brewing temperature of 90–96°C for most filter coffee — at this range, desirable acids (malic, citric, tartaric) and aromatic compounds extract optimally. Below 85°C, coffee tends to be under-extracted (sour, thin). Above 96°C, bitter chlorogenic acid degradation products extract more readily, producing harshness. The difference between brewing at 85°C vs 100°C is detectable in the cup — particularly for single-origin pour-over coffee, where flavour clarity is the primary objective. For Indian brewing contexts: standard masala chai is always prepared at 100°C (the spices and robust black tea require full boiling extraction); but Darjeeling first flush, which is prized for its delicate muscatel flavour, should be brewed at 85–90°C to preserve those aromatics. The KLF04BLEU's 7 temperature presets provide precise control at the key extraction inflection points for each tea and coffee type — not just the convenience of not boiling then waiting for the water to cool.