If you travel to rural areas of China, where Chinese people have a strong knowledge of traditional medicine, you will realise they speak in terms of « hot » and « cold », and as you may guess, it has nothing to do with if the food is hot or not to the tongue. « Hot » for them means that it brings energy to the body, but in excess it can harm the body and get you sick. « Cold » means that it cleans the body but in excess you loose strength and by consequence will also get sick.
Hot food should be taken in the morning and for lunch, as it adds energy (« qi » 气) to your body to help you be active during day time. Cold food should come later on, in the afternoon or eve, to prepare your body for a nice sleep.
To give you a few examples, meat or fish are usually hot, green veggies cold. A good average of fruits are cold, but you have some hot ones too, like durian, lichee, and some are in the middle, half hot half cold, like the apple. As a result, it is said not to eat fruits in the morning in China. This classification of food may seem strange and goes against western diet standards, so welcome to the cultural shock when you travel to China!
Many sayings in modern China make reference to that knowledge of hot (yang) and cold (ying), but I wont say more, this was just a short introduction…
Ok, only one then, about ginger :
« Eating ginger in the morning is better than taking ginseng soup, but eating it at night equals to taking poison. » 早上吃姜，胜过吃参汤；晚上吃姜，等于吃砒霜
Western people will just explain it that way : ginger is a tonic, and you won’t sleep well if you take some in the eve, a bit like coffee.
Some random sources of information:
Chinese Food Therapy (wikipedia)