The latest article is here⇒ [Updated 20220906①] Should green coffee beans be washed with water before roasting, or not?

There is often debate in the coffee industry about whether green coffee beans should be washed with water before roasting or not, but the answer can be found through statistical surveys and analysis.

All you have to do is ask your customers to compare coffee made from beans that weren't washed before roasting with coffee made from beans that were washed before roasting, and decide which one they find more delicious.

[Survey and research methods]

Survey subjects:

20 men and women who regularly drink coffee

Coffee beans used in the survey

①Brazil No.2 Washed Medium Roast (no water washing)
②Brazil No.2 Washed Medium Roast (washed)
③Brazil No.2 Washed City Roast (no water washing)
④Brazil No.2 Washed City Roast (washed)

Roasting method

Roaster: Fuji Royal semi-hot air type
Input amount: 250g
Bottom: 100℃
Temperature change inside the kiln: 1°C increase every 6 seconds up to the first crack, then 1°C increase every 12 seconds

<<Flow of research and investigation>>

1. We asked survey participants to try coffee made with beans ① and ②, rate it out of 10, and also ask for their impressions of the taste.
   (1 point: not tasty, won't buy next time - 10 points: tasty, will buy next time)
   
   
2. We asked the survey participants to try coffee made with beans from types ③ and ④, rate it out of 10, and also ask for their impressions of the taste.
   (1 point: not tasty, won't buy next time - 10 points: tasty, will buy next time)
   
   
3. Conduct a paired t-test on 1 and 2, respectively.
   
   

4. An observation will be made based on the results of the t-test (paired) and the impressions of the survey participants.

[Survey and research results]

Null hypothesis

For medium roasts, there is no difference in the score between coffee whose green beans are not washed before roasting and coffee whose green beans are washed before roasting.

The calculated t value is -4.33, which is smaller than -2.861 (t at 1% significance level with 19 degrees of freedom is 2.861), and falls within the rejection region at the 1% significance level. Therefore, the above null hypothesis is rejected.

《Conclusion》

For medium roasts, there is a difference in the evaluation points between coffee whose green beans are not washed before roasting and coffee whose green beans are washed before roasting.

Null hypothesis

In the case of city roast, there is no difference in the evaluation points between coffee whose green beans are not washed before roasting and coffee whose green beans are washed before roasting.

The calculated t value is -5.29, which is smaller than -2.861 (t at 1% significance level is 2.861 with 19 degrees of freedom), and falls within the rejection region at the 1% significance level. Therefore, the above null hypothesis is rejected.

《Conclusion》

In the case of city roast, there is a difference in the evaluation points between coffee whose green beans are not washed before roasting and coffee whose green beans are washed before roasting.

[Considerations and Summary]

For both medium and city roasts, coffee whose green beans were washed with water before roasting had an average evaluation score that was more than one point higher, and a t-test was used to prove that there was a difference in these averages at a 1% significance level (this difference was not due to chance).

In addition, coffee beans that are washed with water before roasting are
・Clear aftertaste ・I would like to buy it again

Coffee that is not washed before roasting
・Leaves an unpleasant bitter taste on the tongue ・Earthy (compared to water-washed coffee)
There were many negative comments such as:

For this survey and research, we used the highest grade, washed beans, which are relatively resistant to stains when washed in water.
If research is conducted on lower grade beans that produce a lot of dirt when washed in water, or beans that are processed naturally, it is expected that the average evaluation score will differ even more.

For these reasons, if you care about the taste, you should wash your green coffee beans with water before roasting. At our shop, we wash all our green coffee beans with water before roasting.

One thing to note is that washing with water takes a lot of time and water. (It also requires about 2 hours of drying time after washing.) Since labor and water costs are quite high, if your main target customers are more interested in quantity and price than taste, it is better not to wash with water.

In the future, I would like to conduct chemical analysis to clarify the differences in the components of coffee whose green beans have been washed before roasting and coffee whose green beans have not been washed before roasting.

[Supplementary image]