sometimes bitter, sometimes sweet?

@Betty, Thank you for bringing up the question. This is one fact that a lot of people, even some professional tasters, don’t notice. We rely on the papillae on our tongues to physically receive taste materials. Not only do the conditions of these little protrusions change throughout the day and affected by the different things that have passed through them, but also our very own health. The appearance of the tongue is actually one important indicator for TCM doctors during diagnosis. That is why when I don’t feel well, I don’t do tasting at all; the result won’t be true. I am posting an ancient drawing in a TCM book for your reference. There are modern photographic versions with very detail differences and variations, but they are too explicit to be posted here. 

That’s okay when your tongue is white. It helps only very slightly, though and not at all in other conditions. I do not like brushing the tongue coz the endings on the papillae are extremely delicate and can be destroyed. When I brush my tongue at all, I’d do it very very lightly and using a very soft brush. It is, afterall, one’s own health that determines on how effective the taste buds work. On that note, overdose of wine and spicy food adversely affects your senses in tasting very fine tastes such as that of tea. Smoking and strong liquor are the worst enemies in taste. If you notice, those people or even chefs who drink and smoke a lot prefer food with much stronger tastes.