Sugared coffee or tea are less sweet if we drink them after tasting some sweet because,
When we eat sweets a lot ,our taste is used to taste that amount of sweetness. When we eat sweets again, it doesn’t feel sweet because it is relatively not sweet enough .Our senses are calibrated to a continuous condition.
And after this, it only senses relatively .If a chocolate is taken before having tea or coffee, the tea tastes less sweet relatively. However , when we eat more sweeter, we will taste sweetness again. Taste buds are receptors that lock into the molecules that give us a sensation of sweetness. After having something sweet, taste receptors are saturated with molecules. This can be attributed to the relative way in which our brain processes the sense of taste. which our brain becomes familiar to a constant signal , it tends to ignore it and focuses on looking for major changes. So, if our brain is constantly tasting sweet things become the normal and our brain does not notice them much. However, doing something drastic like eating citrous fruits & our brain will signal our brain that as ‘Extremely extra sour’. It is due to sudden change. So, not just our taste , but all of our senses get used to an environment if they are exposed to it long enough.