Follow-up Experiment (Brian)

This week, I conducted a follow-up experiment based on the first experiment. (Click the link if you have not yet checked my last post!). Since the first experiment showed that baking soda is very effective in lowering coffee acidity, but 5g of baking soda is too many to make a nice coffee. So, I would like to find out the effect of changing the amount of baking soda on pH and coffee aroma.

Compare the effect of changing the amount of baking soda on pH and coffee aroma

Hypothesis

The increasing amount of baking soda increases the pH of coffee while decreases coffee aroma

Independent variables

Amount of baking soda added: 0g (control) 1g, 2g, 3g, 4g, 5g

From left to right: 1g, 2g, 3g, 4g, 5g baking soda is added

Experimental procedure

It is similar to the first experiment excepted that I tried to adopt some improvements suggested from the last post like pre-mixing the coffee powder and baking soda as well as measuring the pH when the coffee is cooled down to room temperature

Mixing coffee powder and baking soda 

pH measurement under room temperature 

Result analysis and discussion 

A table showing the change of pH and coffee flavor when adding different amount of baking soda 

Baking soda (g)	Coffee pH	Coffee aroma	Taste
0	5.17	Weak, intensity decreases with an increasing amount of baking soda	Bitter, intensity increases with an increasing amount of baking soda
1	8.16
2	8.38
3	8.67
4	8.56
5	8.70

About the pH...

The effect of baking soda on lowering the coffee acidity is strong even though a very small amount of baking soda is added (1g), but the pH difference is tiny between 1g to 5g. Although pH increases slighting when an increasing amount of baking soda is added, there is still fluctuation in general. The sudden drop in pH from 3g to 4g is out of my expectation. I believed that this may be mainly due to the human errors which I have discussed in the first experiment.

The coffee aroma becomes flat, what happened?

Compared with the first experiment, I found that coffee tastes flatter even in the control. On the contrary, the unpleasant taste of baking soda is strong. I thought that the increasing bitterness of coffee is mainly from baking soda, not coffee. But why....?

Coffee auto-oxidation

When I open the vacuum package of coffee powder, air come contacts with coffee powder. Since air contains around 21% of oxygen, they oxidize and break down many flavor compounds in coffee easily. Although I tried to cover the opening of the package with binder clips after the first experiment, air leakage is still unavoidable.  

My storage method of coffee powder

Storage recommendation# 

National Coffee Association of U.S.A. suggests using a glass container which should be opaque and air-tight to store the coffee powder. A metallic container is fine but makes sure that those metals are inert such as stainless steel.

Conclusion

The experiment supported my hypothesis. Using baking soda to lower coffee acidity is cheap and convenient but it is too hard to avoid the unpleasant taste of baking soda even though they are added carefully. So, we can look for other factors such as the type of coffee beans, degree of roasting and cooking techniques to achieve a better result.  

Date of experiment: 29^th March 2020

By TSE Chun Hei

UID: 3035470955

Reference

# National Coffee Association. (n.d.). How to Store Coffee. Retrieved March 30, 2020, from http://www.ncausa.org/about-coffee/how-to-store-coffee