Lab 5 Sample Report

Introduction

This experiment examined how grind size, water temperature, and extraction time affect total dissolved solids (TDS) and percent extraction (PE) of brewed coffee. Deionized (DI) water was used for all trials to minimize background dissolved solids. TDS was measured directly and used to compute PE according to

\[ PE = TDS \times \frac{m_{\text{brew}}}{m_{\text{dry grounds}}} \]

where all masses are in grams and TDS is expressed as a decimal fraction.

Methods

Three tests were conducted:

Test 1 — Grind Size (water TDS: 3.94 ppm): Coarse, medium, and fine grinds were brewed at a fixed temperature and extraction time.

Test 2 — Water Temperature (water TDS: 0.44 ppm): Brews were prepared at 70 °C and 99 °C using a medium grind.

Test 3 — Extraction Time (water TDS: 7.68 ppm): Brews were pulled at 1 minute and 10 minutes. For the 10-minute brew, TDS was sampled every minute to track extraction over time.

The mass of the empty carafe (324.37 g) was subtracted from all post-brew mass readings.

Results

Summary Table

Brew	Grounds (g)	Brewed (g)	TDS (%)	PE (%)
Test 1 — Grind Size
Coarse	25.70	376.92	0.027%	0.4%
Medium	25.42	333.93	1.320%	17.3%
Fine	25.97	318.23	1.620%	19.9%
Test 2 — Temperature
70 °C	25.89	345.98	1.300%	17.4%
99 °C	25.62	325.28	1.370%	17.4%
Test 3 — Extraction Time
1 min	24.94	327.10	1.170%	15.3%
10 min	25.88	315.68	1.680%	20.5%

Analysis

Deionized (DI) water was used for all trials, and measured background TDS values ranged from 0.44 to 7.68 ppm. These values are several orders of magnitude lower than brewed coffee concentrations (13,000–16,000 ppm) and therefore negligible in comparison. The dissolved solids measured in each brew can be attributed almost entirely to extracted coffee compounds rather than to mineral contributions from the water itself. The slight variation in measured water TDS likely reflects minor instrument fluctuation rather than meaningful chemical differences.

Turning to the brews, grind size had by far the most pronounced effect on TDS (Figure 1). The fine grind produced the highest TDS at 1.620%, followed by the medium grind at 1.320%, while the coarse grind yielded only 0.0274%. This relationship is physically intuitive: finer grinding increases total surface area and reduces diffusion distance within particles, allowing water to dissolve soluble compounds more efficiently within the fixed contact time. The coarse grind’s extremely low TDS reflects limited surface area and poor mass transfer under the same brewing conditions. By contrast, water temperature had a comparatively modest effect on TDS, with only a 0.070% difference between the 70 °C (1.300%) and 99 °C (1.370%) brews. Within this temperature range, particle size clearly exerted the dominant control over concentration.

The same pattern holds for percent extraction (Figure 2). The coarse grind achieved only ~0.40% extraction, confirming severe under-extraction. The medium grind reached approximately 17.3%, while the fine grind achieved ~19.8%, approaching the commonly cited 20% benchmark. Unlike TDS, which reflects concentration, percent extraction represents total solute yield relative to the mass of dry grounds. The fine grind’s proximity to 20% indicates near-optimal extraction efficiency under the tested conditions, while the medium grind falls just below the ideal range. Temperature again produced only minor differences, increasing extraction from ~17.4% at 70 °C to ~17.9% at 99 °C, a measurable but secondary effect compared to grind size.

Comparing these results (Figure 3) to industry benchmarks of 1.2–1.5% TDS and 18–22% extraction, several brews fall very near although not within the optimal zone. The fine grind and the 10-minute extraction both approach 20% PE, while the medium grind and both temperature trials cluster slightly below but within reasonable range. Only the coarse grind is clearly outside acceptable extraction conditions.

Finally, the per-minute TDS data from the 10-minute extraction (Figure 4) reveal a clear rise-and-fall pattern. TDS increased sharply during the first three minutes, peaking near 3.58%, then gradually declined to 1.68% at ten minutes. This behavior is consistent with diffusion-limited extraction. In the early stage, highly soluble compounds such as organic acids, simple sugars, and light aromatics dissolve rapidly, driving concentration upward. As these compounds become depleted, dissolution slows while additional water accumulates in the vessel, diluting the brew and lowering TDS despite continued extraction. Total extraction (PE) continues to increase over time even as concentration falls, highlighting the distinction between strength and yield. Extrapolating further, extended brewing would likely continue to raise extraction slightly while decreasing concentration and increasing the contribution of less desirable bitter compounds.

Overall, grind size exerted the strongest influence on both concentration and yield, extraction time played a significant secondary role, and temperature had the least impact within the tested range. The results are consistent with mass transfer principles and with established industry extraction standards.

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Appendix: Raw Data

Table A1. Water TDS in ppm measured prior to each test (DI water used).

Test	TDS
Test 1 — Grind Size	3.94
Test 2 — Temperature	0.44
Test 3 — Extraction Time	7.68

Table A2. Brew measurements and calculated values.

Brew	Test	Grounds (g)	Brewed (g)	TDS (%)	PE (%)
Coarse	Grind Size	25.70	376.92	0.027%	0.4%
Medium	Grind Size	25.42	333.93	1.320%	17.3%
Fine	Grind Size	25.97	318.23	1.620%	19.9%
70 °C	Temperature	25.89	345.98	1.300%	17.4%
99 °C	Temperature	25.62	325.28	1.370%	17.4%
1 min	Extraction Time	24.94	327.10	1.170%	15.3%
10 min	Extraction Time	25.88	315.68	1.680%	20.5%

Table A3. Per-minute TDS samples for the 10-minute extraction (Test 3).

Time (min)	TDS (% dissolved)
1	1.8300%
2	2.9800%
3	3.5800%
4	3.4000%
5	3.1800%
6	2.7800%
7	2.5900%
8	2.3200%
9	2.1600%
10	1.6800%