Over-extraction & Under-extraction¶

Extraction Concepts Extraction yield: Percentage of coffee mass dissolved into brew. Target: 18-22% for optimal balance. Under-extraction: <18%. Over-extraction: >22%. Both create unbalanced, unpleasant cups. Avoid extremes for quality. Under-Extraction (<18%) Flavor Characteristics Sour, tart, acidic (harsh, not bright). Salty taste possible. Grassy, vegetal, green flavors. Cereal, grainy notes. Thin body, watery. Lack of sweetness. Short aftertaste. Unbalanced, incomplete. Causes Grind too coarse (low surface area). Brew time too short. Water temperature too low. Insufficient agitation. Coffee dose too low. Improper brewing technique. Visual Indicators Espresso: Very fast shot (<20 seconds). Blonde, thin crema. Pour-over: Very fast drawdown (<2 minutes). French press: Short steep (<2 minutes). Light color in cup. How It Tastes Sharp acids dominate. No sweetness to balance. Feels incomplete. Unpleasant tartness. One-dimensional. Sour aftertaste. "Green" or "raw" impression. Underdeveloped character. Fixing Under-Extraction Grind finer (primary solution). Increase brew time. Raise water temperature. Increase agitation (if appropriate). Increase dose (sometimes). Check technique. Over-Extraction (>22%) Flavor Characteristics Bitter (harsh, not pleasant). Astringent, drying mouthfeel. Hollow, empty flavor. Flat, dull, lifeless. Burnt, ashy notes (extreme cases). Harsh aftertaste. Unpleasant lingering. One-dimensional bitterness. Causes Grind too fine (excessive surface area). Brew time too long. Water temperature too high. Excessive agitation. Coffee dose too high (sometimes). Over-doing technique. Visual Indicators Espresso: Very slow shot (>35 seconds). Dark, thin stream. Pour-over: Very slow drawdown (>5 minutes). French press: Extended steep (>6 minutes). Dark color in cup. How It Tastes Bitterness dominates palate. Astringency dries mouth. No sweetness or brightness. Harsh, unpleasant. "Burnt" or "ashy" impression. Lingering bad aftertaste. Exhausted coffee character. Fixing Over-Extraction Grind coarser (primary solution). Reduce brew time. Lower water temperature. Reduce agitation. Reduce dose (sometimes). Check technique. The Target Zone (18-22%) Optimal Extraction Sweet, balanced flavor. Acidity bright, not sour. Complexity and clarity. Body appropriate. Clean aftertaste. Pleasant lingering. Desire for another sip. Quality expression. Why This Range Early extraction (0-18%): Acids, salts, sugars, lighter compounds. Sweet spot (18-22%): Complex flavors, sweetness, balance. Late extraction (22%+): Bitter compounds, astringency, harshness. Target includes good, excludes bad. Variability Light roasts: May prefer 19-21% (avoid harsh). Medium roasts: 18.5-22% full range. Dark roasts: 18-20% (avoid bitter). Origin variation. Personal preference. But range holds generally. Measuring Extraction Refractometer measures TDS. Formula: Extraction Yield % = (Brew Weight × TDS%) / Coffee Dose × 100. Precise measurement. Gold standard. Covered in TDS & Extraction Yield section. Extraction & Brewing Variables Grind Size (Primary Variable) Finer grind: Higher extraction (more surface area). Coarser grind: Lower extraction (less surface area). Most powerful extraction control. First adjustment always. Contact Time Longer time: Higher extraction. Shorter time: Lower extraction. But diminishing returns. First 30 seconds extract 15-18%. Next 3 minutes extract 2-4% more. Time-extraction not linear. Water Temperature Higher temp: Higher extraction rate. Hotter water dissolves more. Chemical reaction speed increases. 3-5°C change noticeable. But grind size more powerful. Agitation More turbulence: Higher extraction. Fresh water contact accelerates. Pour-over technique. Immersion stirring. Pressure (espresso). Moderation important. Coffee-to-Water Ratio Does NOT directly control extraction yield. Controls strength (TDS). Can affect extraction indirectly. More coffee can buffer over-extraction. But extraction vs. strength different. Simultaneous Under & Over-Extraction Uneven Extraction Channeling in espresso. Some grounds over-extract (bitter). Other grounds under-extract (sour). Average extraction may measure fine. But cup quality poor. Why averages mislead. Tasting Clues Sour AND bitter simultaneously. Confusing flavor. Muddy, unbalanced. Technique problem likely. Distribution, channeling, uneven flow. Fix preparation, not just extraction target. Solving Address unevenness: Better distribution (WDT). Level tamping. Consistent grind. Appropriate basket. Even saturation. Technique before numbers. Method-Specific Extraction Espresso Target: 18-22% typical (some prefer 18-20%). Time: 25-30 seconds. Pressure amplifies extraction. Small changes dramatic impact. Ratio affects strength, grind affects extraction. Pour-Over Target: 18-22%. Time: 3-4 minutes. Gentler extraction than espresso. More forgiving. Visible indicators (fast = under, slow = over). Technique affects evenness. French Press Target: 18-22%. Time: 4 minutes standard. Immersion provides even extraction. Coarse grind important. Extended time over-extracts. Simple method. Cold Brew Target: Usually lower (15-20%). Long time compensates for cold. Room temp faster than refrigerated. Over 24 hours: Over-extraction risk. Different extraction chemistry. Extraction Troubleshooting Sour but Not Under-Extracted Light roast underdeveloped in roasting. Problem not brewing. Or water too cool. Or coffee too fresh (excessive CO2). Check roasting and freshness first. Bitter but Not Over-Extracted Dark roast inherently bitter. Stale coffee (quinic acid). Dirty equipment (rancid oils). Or actually over-extracted (measure). Multiple causes possible. Measuring to Confirm Don't rely solely on taste. Measure TDS and calculate extraction. Taste can mislead. "Sour" from stale coffee, not under-extraction. Numbers provide objectivity. Refractometer valuable tool. Extraction & Quality High quality coffee more forgiving. Broad extraction window tastes good. Lower quality coffee narrow window. High altitude dense coffee forgiving. Defective coffee: No extraction fixes defects. Start with quality beans.

Related Notes: - Coffee Terminology MoC