Dialling In Espresso: The Art of the Perfect Grind

Espresso is the most technically demanding coffee brewing method, and nowhere is this more apparent than in grinding. While pour-over and French press brewing are forgiving of minor grind inconsistencies, espresso magnifies every variable. A shift of just a few microns in particle size can transform a balanced, sweet shot into something sour or bitter. For many home baristas, learning to dial in espresso grind is the steepest part of the learning curve—but also one of the most rewarding to master.

Understanding Espresso Extraction

Before we can dial in, we need to understand what we're adjusting for. Espresso brewing forces hot water through a compact bed of finely ground coffee at high pressure, typically 9 bars. This pressurised extraction happens rapidly—a well-made shot takes 25-35 seconds from the first drip to completion.

During this brief window, water dissolves and emulsifies compounds from the coffee. We're after the sweet, complex, aromatic compounds while trying to avoid extracting harsh, bitter, or astringent elements. The grind size primarily controls the rate of extraction by affecting how quickly water flows through the coffee bed.

Signs of Incorrect Extraction

Under-Extraction

When grind is too coarse (or other variables like dose are wrong), water flows through too quickly and doesn't extract enough from the coffee. Under-extracted espresso tastes sour, acidic, and thin. It often looks pale and watery, lacking the rich golden-brown colour and crema of good espresso. The shot may run very fast—sometimes just 10-15 seconds.

Over-Extraction

When grind is too fine, water struggles to pass through the coffee bed. Too many compounds are extracted, including unpleasant bitter and astringent ones. Over-extracted espresso tastes harsh, bitter, and sometimes ashy. The shot runs slowly—40+ seconds—and may even choke completely, with only drops coming out despite the pump running.

The Sweet Spot

Properly extracted espresso is sweet, balanced, and complex. It has a rich body, visible crema, and showcases the positive flavour characteristics of the coffee—whether that's fruity acidity in a light roast or chocolatey depth in a darker roast. The shot runs in approximately 25-35 seconds (this varies by coffee and preference) and the flow appears smooth and steady.

The Dialling-In Process

Here's a systematic approach to dialling in espresso grind:

Step 1: Establish Your Baseline

Start with a known recipe. For most setups, 18g of coffee in a standard double basket, yielding approximately 36g of espresso, is a good starting point. Use a scale to measure both your dose and yield accurately—eyeballing doesn't work for espresso.

Set your grinder to a middle-fine setting and pull a shot. Time from when you start the pump to when you stop it. Observe the flow—does it start almost immediately, or is there a significant delay? Is the flow steady or spurting? Note the colour of the espresso as it pours.

Step 2: Adjust Based on Time

If your shot runs too fast (under 20 seconds), adjust finer. If it runs too slow (over 40 seconds) or chokes, adjust coarser. Most grinder adjustments should be small—1-2 notches on a stepped grinder, or a small movement on a stepless grinder.

After each adjustment, purge a small amount of coffee through the grinder to clear any grounds from the previous setting. Then dose fresh, pull a shot, and time again.

Step 3: Taste and Refine

Once you're in the right time range, taste becomes your guide. If the shot is sour and thin, try grinding slightly finer to increase extraction. If it's bitter and harsh, try grinding slightly coarser. Small adjustments matter at this stage—you're fine-tuning, not making major corrections.

Keep notes on your adjustments and results. Over time, you'll develop intuition for how much to adjust based on taste observations.

Common Dialling-In Challenges

Channeling

Channeling occurs when water finds paths of least resistance through the coffee bed, over-extracting those areas while under-extracting others. Signs include uneven flow from the portafilter (spurting or one side running faster), spritzing during extraction, and inconsistent flavour shot to shot.

Channeling is often a distribution or tamping problem rather than a grind problem. Ensure your coffee is evenly distributed in the basket before tamping. Tools like WDT (Weiss Distribution Technique—using a thin needle or wire to stir and distribute grounds) can help. Tamp evenly with consistent pressure.

Stale Coffee

Coffee that's too fresh (less than 5-7 days off roast) or too old (more than 4-6 weeks) can be difficult to dial in. Very fresh coffee releases excessive CO2 during extraction, causing unstable flow. Old coffee, having lost volatile compounds, may extract differently than fresh. Dial in with coffee in the optimal window (1-4 weeks off roast for most espresso roasts) for most consistent results.

Environmental Factors

Humidity affects coffee grinding and extraction. On humid days, coffee absorbs moisture and may require coarser grinding. On dry days, you may need to grind finer. Temperature changes also affect extraction—if your grinder or espresso machine is cold, your first shots may not reflect your dialled-in settings.

Grinder Retention

Many grinders retain ground coffee in the chamber and chute. When you adjust grind size, the retained coffee is from the previous setting. Always purge a small amount after adjusting to clear old grounds. Single-dose grinders are designed to minimise retention for exactly this reason.

Beyond Grind: Other Variables

While grind size is the primary dial-in variable, other factors interact with it:

Dose

The amount of coffee in your basket affects extraction. Higher doses (more coffee) generally require coarser grinding; lower doses require finer grinding. Most home baristas keep dose constant and adjust grind, but some recipes call for dose adjustment as well.

Yield

How much espresso you produce affects flavour. Shorter shots (ristrettos) are more concentrated but may be under-extracted. Longer shots (lungos) are more dilute but extract more from the coffee. Adjusting yield is another tool for fine-tuning flavour.

Temperature

Water temperature affects extraction rate. Lower temperatures extract less; higher temperatures extract more. Some espresso machines allow temperature adjustment. If your grind and recipe are correct but shots taste under- or over-extracted, temperature may be a factor.

Developing Your Palate

Dialling in improves as your palate develops. Taste shots critically—not just for general pleasantness, but for specific characteristics. Is there excessive sourness? That suggests under-extraction. Harsh bitterness or dryness? Over-extraction. The more you taste and correlate with your adjustments, the better you'll become at achieving your target profile.

Consider keeping a simple espresso journal: date, coffee, grind setting, dose, yield, time, and tasting notes. Over time, patterns emerge that inform your dialling-in process.

Dialling in espresso can be frustrating initially, but it's also the path to exceptional home espresso. Each challenging shot teaches you something about extraction. With practice, you'll dial in new coffees quickly and consistently produce shots that rival your favourite cafe.