The question of whether green coffee beans should be washed before roasting is often debated in the coffee industry, but a statistical survey and analysis can provide an answer.

Customers should be asked to compare coffee made from unwashed green beans and coffee made from washed green beans before roasting, and to determine which they found more delicious.

【Survey Methodology】

《Survey Dates》

May 2021 - June 2021

《Survey Participants》

20 men and women who regularly drink coffee

《Coffee Beans Used in Survey》

① Brazil No.2 Natural Medium Roast (unwashed)
② Brazil No.2 Natural Medium Roast (washed)
③ Brazil No.2 Natural City Roast (unwashed)
④ Brazil No.2 Natural City Roast (washed)
*Green beans were washed with tap water as if rinsing rice, then thoroughly dried with a fan.

《Roasting Method》

Roaster: Fuji Royal semi-hot blast type
Batch size: 250g
Bottom temperature: 100℃
Drum temperature change: 1℃ rise every 6 seconds until first crack, then 1℃ rise every 12 seconds

《Survey Procedure》

1. Participants drank coffee made from beans ① and ② that had been roasted one week prior (participants were not told which coffee had washed green beans). They rated the coffee on a scale of 1 to 10 points and provided comments on the taste.
   (1 point: Not delicious, would not buy again ~ 10 points: Delicious, would buy again)
   
   
2. Participants drank coffee made from beans ③ and ④ that had been roasted one week prior (participants were not told which coffee had washed green beans). They rated the coffee on a scale of 1 to 10 points and provided comments on the taste.
   (1 point: Not delicious, would not buy again ~ 10 points: Delicious, would buy again)
   
   
3. A paired t-test was conducted for steps 1 and 2 respectively.
   
   

4. Discussion was conducted based on the results of the paired t-test and participants' comments.

 【Survey Results】

《Null Hypothesis》

For medium roast, there is no difference in evaluation scores between coffee made from unwashed green beans and coffee made from washed green beans before roasting.

The calculated t-values were -4.33 and -2.861, which are smaller than the t-value of 2.861 at a 1% significance level with 19 degrees of freedom. Therefore, they fall within the rejection region at a 1% significance level, and the null hypothesis is rejected.

《Conclusion》

For medium roast, there is a difference in evaluation scores between coffee made from unwashed green beans and coffee made from washed green beans before roasting.

《Null Hypothesis》

For city roast, there is no difference in evaluation scores between coffee made from unwashed green beans and coffee made from washed green beans before roasting.

The calculated t-values were -5.29 and -2.861, which are smaller than the t-value of 2.861 at a 1% significance level with 19 degrees of freedom. Therefore, they fall within the rejection region at a 1% significance level, and the null hypothesis is rejected.

《Conclusion》

For city roast, there is a difference in evaluation scores between coffee made from unwashed green beans and coffee made from washed green beans before roasting.

【Discussion and Summary】

For both medium and city roasts, coffee made from green beans washed before roasting received an average evaluation score of at least 1 point higher. The t-test also proved that this average difference was significant at a 1% level (not a random difference).

Furthermore, coffee made from green beans washed before roasting received many positive comments such as:
・Clean aftertaste
・Would buy again

While coffee made from unwashed green beans before roasting received many negative comments such as:
・Unpleasant bitterness remaining on the tongue
・Earthy (compared to washed coffee)

In this survey, the coffee made from washed green beans ultimately received higher taste evaluations, but

・Our roasting profile may have been suitable for washed green beans.
・Brazil No.2 Natural green beans may have been suitable for washing.

Given various possibilities such as these, it cannot be unequivocally stated that washing green beans improves the taste.

However, for roasters selling expensive specialty-grade coffee beans, it is important to repeatedly conduct such surveys to understand whether their main customers prefer coffee made from washed green beans or unwashed green beans.

【Supplementary Images】