Since demand is growing slowly you can increase supply also. In my GB campaign I was able to keep prices of ivory and spices at 25 to 26. With other commodities this is very difficult since you do not control the supply. At the end of my campaign coffee became scarce and the price went up to 21 gold. If I capture parts of South America I always look at the trade screen to watch the prices. If the price of sugar is very low I try if I can build a cotton or a coffee plantation over there.

In 1795 I destroyed the UP. They had a two huge trade fleets, one in the East Indies and one on the ivory at Madagascar. Since these were destroyed, the supply went down and prices of spices went up to 34 and of ivory went up to over 30.