First experiment (Kiannie)

Detail of the first experinment

• Topic

          Observing the effect of coffee grind size on time needed in hand-drip coffee and determine its effect on acidity/taste

•    ingredients

         For 4 trial

         - 80g Coffee bean ( Medium roast, guatemala casi cielo)

         - 1200 ml Hot water 

• equipments

         - Cone filter

         - Cone shape pour over dripper

         - Burr grinder

         - Gram scale ( include timer )

         - Slow pouring kettle

• hypothesis 

              The finer grind, more time is required for dripping while the coarser the grind reduce total time required.

              The longer time required, the higher extraction and less sour and bitter taste is produced, the shorter time required, the lower extraction and more sour taste is produced.

• procedures 

          1. Measure 20g coffee bean into 4 different cups respectively and mark the grinding degree    (1,5,9,13) on the paper cup.

       

            (Finest) 1----------------5----------------9----------->13 (coarsest)

         

            2. Grind the coffee bean according to the degree marked on the cup.

                  

            3. Place filter paper in the dripper and rinsk it with boiled water.

            

            4. Place the ground coffee in the filter and level it.

            5. Start the timer and pour water to wet the coffee bed.

            6. Allows it to rest for 25 seconds.

           7. Pour water continuously in a circular manner.

               (from the middle to periphery and from the periphery back to the middle)
          
               
           8. Stop when 400 ml reached.
             
               
           9. Wait until the filter is completed and stop the time. Record the time used.
          10. Wash all the equipment and repeat from step 3 to 9 with each grind size

Preminary trial result

    For the cooking experiment, grind size set at 4 degree, from finest to coarsest.
Time for dripping of each grind size is measured (include 25 seconds of resting time)

The table below show the experimental result:

Grind size	1	5	9	13
Time	4’07”	3’14”	2’26”	2’10”

    From the experimental results, there is a general trend showing how grind size affects the time required for dripping. The time reduces from finest grind size to coarsest grind size. The experiment fit the hypothesis of which the finer grind, provides a larger contact surface area and slow down the flow of water which increase the total time while the coarser the grind provides a smaller contact surface area and speed up the flow which reduce total time. This can be explained by imagining a glass filled with  sand and another glass filled with larger pebbles. Water will obviously drip faster in the glass filled with pebbles because it has a smaller surface area, water can pass in a quicker rate. 

Why this research important?

    You may think that knowing the dripping time for each grind size is not necessary and important but what if the dripping time also affect the taste and pH of the coffee? As mentioned above, different grind size affect the flow of water. The speed of flow may eventually affect the extraction rate. Different level of extraction has a great impact on the taste and aroma of coffee. Therefore, a further pH test and tasting is used to determine whether higher extraction will result in a more sour taste or more bitter taste. After knowing what taste will be given if the longer time or shorter time is used, you can make a coffee fitting your personal preference by adjusting the coffee grind size.

pH test using teststrips

  Grind size 1                       5                                9                                13

        From the teststrips (bottom test) , it shows a similar result for all grind size which is around pH 5. This shows the pH value doesn't change a lot when different grind size is used. Although the testtrips can't accurately shows the pH value, it provides another information that ascorbic acid (second test) is present in the coffee. The sourness of coffee may contribute by ascorbic acid.

        As the pH value does not change a lot, a further test is used to determine the taste of coffee-- coffee tasting by a barista. There are four steps of coffee tasting, which is smell,slurp,locate and describe. Barista is more likely to identify the difference in taste according to 4 stesps. Thus, the coffee is then taste by a barista in a random manner and allows her to arrange the order according to the bitterness and sourness of coffee which people concern most.

Grind size	1	5	9	13
Bitterness(1 =most bitter )	1	2	3	4
Sourness (1=most sour)	4	3	2	1

      The coffee with finer grind produce a stronger taste,higher bitterness in coffee while the coffee with coarser grind produce the lighter taste with more sourness. This can be explained by the extraction rate of coffee. As more time is required for finer grind, higher extraction will result. Over-extraction may occur which take out too much soluble flavour from the coffee and result in bitterness. Less time is required for coarser grind, lower extraction will result. Under-extraction may occur which haven't take enough flavour from the coffee grind. The coffee become less balanced.

Problems identify and improvement measures

1.  Single data may not be accurate enough

     In final experiment, 3 sample will be made for each grind size. Taking an average will improve the      accuracy of data.

2.  400 ml of water used in not constant for each trial

     Try to pour as slow as possible when 400 ml is reached to ensure the data is more of less the same.   Allow the maximum error in around +- 1ml. If the trial exceed 401 ml, the trial should not be used and repeat once.

3.  Coffee Tasting by single barista is not fair enough
 
        In final experinment, the coffee should be taste by more than 5 barista to ensure the fairness. Avereage data should be taken. For barista who are required to taste the coffee should not knowing which coffee is created by which grind size. Coffee should be given in a random manner. Barista should rinsk their mouth with water before tasting another cup of coffee to ensure the accuracy.

4.  The taste of coffee will change along time, fair comparison is difficult as there is a time gap among each trial.

     Use the last trial of each grind size. After dripping the coffee, stores coffee in an airtight thermos to reduce the chance of oxidfation of coffee. Do each trial as fast as possible and taste the coffee as soon as possible to minimise the error.

Yiu Cheuk Laam (UID:3035564756)