Many people are only familiar with the charcoal briquettes found at the local grocery store. These briquettes are far from being pure charcoal. The manufacturers begin with charcoal which is then ground and combined with fillers and binders to make the charcoal "go further". It also has non-wood substances such as petroleum coal added to each briquettes. Just because you have a "light coat of gray ash" covering each briquette does not solve the problem. The truth of the matter is that impurities burn all the way through the briquettes and you continue to burn these impurities while cooking your meat.
One way to avoid this is to use lump charcoal as it is very pure and clean. There are no foreign substances and all the impurities found in natural wood have been eliminated during the process of turning it into charcoal. It burns much hotter and faster than the regular charcoal briquettes. If you're doing some grilling you will not find a better heat source. If you're barbecuing will find that you need to add smaller quantities more often in order to control the heat. If you have a chance to use lump charcoal by a bag and began to have some fun.