There have been a few times when Front Street recommended Mandheling after consulting the customer who didn't like sour coffee, but the guest said that he had drunk Mandheling, and it was a sour ......Generally, the flavor expression of Mandheling is herbaceous, nutty, chocolate, caramel, and there will be no sour taste. So is it possible that Mandheling has a sour taste? Yes, and it's simple, just don't roast the beans so deep when roasting them. 
In our impression, the coffee beans of Ethiopia and Kenya are sour, and the coffee beans of Blue Mountain and Mandheling are bitter. But in fact, the acidity and bitterness of coffee do not have much to do with the region, but mainly with the degree of roasting.
In coffee roasting, the development period after the first burst point is called the development period, which will determine the final flavor trend of the coffee, the shorter the development period, the shallower the roasting degree, and the more sour the coffee flavor trend; Conversely, the longer the development period, the longer the caramelization reaction, the deeper the roast and the more bitter the flavor tends to be.
Sour and bitter are only the main notes of coffee flavor, but if the coffee only has a sour taste or only bitterness, it is not pleasant, and the most important thing is to highlight the sweetness and aroma.
For example, Kenyan coffee beans are as well known in the consumer market for light roasting as they are for dark roasting, and lightly roasted Kenyan coffee exhibits a bright acidity like plums and cherry tomatoes; The dark roast Kenyan coffee is clean, rich, bittersweet and sweet like dark chocolate. 
Some friends may wonder why Mandheling and Blue Mountain coffees still insist on dark roasting in the era of the outbreak of light roasted coffee, coupled with some remarks such as "roasting coffee beans deep to cover up the flawed taste", making everyone wonder if the quality of these dark roasted coffee beans is not as good as that of light roasted coffee beans.
It is undeniable that whether it is high-quality coffee beans or low-quality coffee beans, if they are roasted to the extent that they are close to charcoal, the taste that comes out is highly consistent, and it is bitter to doubt life. But it's clear that the taste of these dark roast coffees is not simply bitter, but bitter and sweet, whether it's Blue Mountain or Mandheling. If there are beans of poor quality in them, then the feedback on the taste will make it impossible to hide. 
The beans of Blue Mountain and Mandheling were already famous before the rise of light roast coffee, and the labels of these coffees were mellow, balanced, and full-bodied, and even Blue Mountain was considered the standard "coffee flavor". In this case, maintaining the same flavor quality is exactly what these beans are all about! Of course, under the wave of "specialty coffee", you can still drink light roasted Blue Mountain and Mandheling coffee with a fruity sour taste in some shops.
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