If you'd like to just enjoy a hot cup of herbal infusion, then the standard brewing guidelines work fine. However, depending on what specific compounds you wish to extract from our herbal infusions (be it electrolytes or antioxidants/phytochemicals), different brewing temperatures will apply.
To both extract and preserve the phytochemicals present within the herbs, a lower temperature of brewing and for longer is recommended. Phytochemicals change upon the application of heat and may result in two opposite phenomena: the thermal degradation reducing their concentration, and the matrix softening effect which increases phytochemical extractability resulting in a higher concentration respect to the herb (i.e. enabling the leaching of soluble compounds in water). The final effect of applying heat on phytochemical concentration depends on the structure of the herb matrix and the chemical nature of the specific compound (anthocyanins vs carotenoids).
Different vitamins will be affected to different extents in terms of temperature and the addition of water. As a general rule degradation of vitamins starts to occur when exposed to temperatures of greater than 48 °C. In particular, vitamin C begins to denature at temperatures as low as 30 °C, according to a study in the International Journal of Scientific and Technology Research. The negative effects of heat increase significantly at 60 and even more at 70 °C.
It is important to note that your hot water will be losing heat rapidly and will not remain at the temperature you had brewed at for very long, especially if you are pouring it into a brewing vessel/teapot which is at room temperature. As a rule of thumb, for every minute left, the water decreases in temperature by 10°C. So even if you add water which may be a little too hot, you'll still be extracting some of the phytochemicals, vitamins and compounds as they do not degrade instantaneously.
For grain tisanes and dry berry infusions, a higher temperature is naturally recommended, as more heat over a longer duration is required to penetrate the tougher outer layers.
We've added our recommended variations to the temperatures and brewing times for each of our infusions to be able to balance extraction with degradation of the active compounds, noted as the Health Brewing Guidelines below.