First Experiment (Chloe)
Details of first experiment
Topic
Investigating the level to which water chemistry affects the pH value of cold brewed and hot brewed coffee.
Hypothesis
The addition of magnesium concentrate and buffer concentrate will have a significant effect on the hot brewed coffee but not on the cold brewed coffee.
- Equipment used
1 electric scale
pH test paper strips
(For the concentrate)
1 300ml glass jar
1 small measuring spoon
(For the cold brew)
2 700ml glass jars
1 cheesecloth
2 mesh strainers
1 measuring jug
1 funnel
1 large bowl
(For the hot brew)
1 kettle
1 measuring jug
1 coffee funnel
filter paper
- Ingredients used
(For the concentrate)
10g epsom salt
3.4 g baking soda
200 ml distilled water
(For the cold brew: 2 batches)
74g espresso beans with a medium-coarse grind
996ml distilled water
100ml hot distilled water
2g magnesium-and-buffer concentrate
(For the hot brew: 2 cups)
32g espresso bean with a medium grind
1g magnesium-and-buffer concentrate
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Experimental procedures
(Making the concentrate)
1. Measure out 10g epsom salt and 3.4g baking soda. Add them into the jar.
2. Put jar on electric scale before adding water until total reaches 200ml.
3. Stir to make sure everything is dissolved. Store in fridge.
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(Making the cold brew)
1. Pour 37g freshly grinded beans into each jar.
2. Pour some of the hot distilled water over the grounds just until all the grounds are moistened, allowing for hot bloom. There is no need to use up the 100ml of hot water.
3. Add 498ml unheated distilled water to each jar. In one jar add additional 2g from the magnesium-and-buffer concentrate.
4. Let sit in refrigerator for 18 hours.
5. Strain the liquid through both cheesecloth and strainers, washing in between the two batches, and store in fridge.
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(Making the hot brew)
1. The two coffees will be made sequentially. The 'control' cup, brewed with pure distilled water, will be made first. Boil 300ml distilled water.
2. Position the mug and the coffee funnel on the electric scale. pour 15ml hot water on the filter to wet the paper. Discard the water collected in the cup.
3. Add coffee grounds and shake to level.
4. Pour 16-25g hot water on the grounds in a circular motion and allow the grounds to bloom, around 30 seconds.
5. Pour around 37ml hot water on the grounds in a circular motion every 20 seconds until it reaches 250ml.
6. When the coffee funnel stops dripping, remove and wash. Let coffee cool.
7. After washing all apparatus used, add 1g magnesium-and-buffer concentrate to the distilled water in the pot and boil. Repeat steps 2 to 6.
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Preminary trial results
In the kitchen experiment, the importance of water quality on the final outcome of a coffee is being investigated. Both the hot brew and the cold brew have a 'control' batch which is brewed with pure distilled water. pH paper strips are used to see if there are any significant changes in the pH levels.
Between cold brew (distilled water on the left, remineralized water on the right):
Both pH paper tests register as a pH level of 5.
Between hot brew (distilled water on the left, remineralized water on the right):
Both pH paper tests register as a pH level of 4.
It is clear that between each method, both coffees brewed with distilled water or brewing with remineralized water reach a similar pH level. However, hot brewed coffee was shown to be slightly more acidic, having a pH level of 4 while cold brew have a pH level of 5. This is likely due to the fundamental extraction method cold brew utilizes, which is a slow immersion extraction in low temperature. This way the more acidic oils are not released fully and the resulting brew is less acidic, unlike with quick, high temperature extraction methods like pour over coffee.
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Identifying problems and ways of improvement
1 pH tester papers are not a very reliable source for measuring specific levels of pH, and can come across as quite vague and unhelpful since it only offers a general category but not the degree, especially since the pH levels of the tested subjects are very similar. The use of pH meters would be more helpful in identifying the actual acidity of the drink.
2 There should be a tasting panel to experiment if the subjects would eventually start to taste the difference between coffee brewed from distilled and remineralized water. At the moment I had focused on more objective measurements like pH levels, but everyone has different preferences for coffee and the effect of minerals in the brew water may interfere with other aspects of the taste of coffee, so asking people to comment should be a needed addition.
3 Since I am making the hot brew coffee one at a time, the time the first cup has to cool down may affect its taste due to its exposure to light and air, and the oils in the coffee turning rancid. Thermo jars may be used to store the finished coffee while the second cup is brewed so I can minimize the risk of environmental factors. Another process which may also have altered the time in which the coffee grounds were exposed to the air and oxidation allowed to happen before brewing, since I had ground coffee beans for both cups before starting to brew. To minimize the effect this may have on the outcome of the final experiment, coffee beans should be ground immediately prior to each cup, instead of pre-ground in a larger batch.
4 The current ratios do not create a large enough difference between coffee brewed with distilled and remineralized water. A larger amount of the magnesium-buffer concentrate could be added to the brew water to see how much is needed for a noticeable difference in both pH levels and taste.
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By: Pang Ching I (3035696511)
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