The Complete Guide to Making Cold Brew Coffee at Home

Cold brew coffee has exploded in popularity — and for good reason. It’s smoother, less acidic, and more forgiving than any other brewing method. But most home guides get the details wrong, and you end up with something weak, sour, or gritty.

At Mumbles, we’ve been steeping our signature 18-hour cold brew in-house since day one. Every batch starts with single-origin Ethiopian beans, a deliberate grind size, and filtered water — nothing more. That discipline has taught us what actually matters and what most guides skip entirely.

This article gives you everything: the correct ratio, grind, water temperature, steep time, and straining technique. Follow it once, and you’ll never buy bottled cold brew again.

What Is Cold Brew Coffee — and Why Does It Taste So Different?

Cold brew is not iced coffee. This distinction matters.

Iced coffee is brewed hot and poured over ice. It retains all the bright, sharp acidity of a standard extraction — and when it dilutes, it gets watery fast. Cold brew, on the other hand, never touches heat. You steep coarse-ground coffee in cold or room-temperature water for 12 to 24 hours. No heat. No rush.

The result is chemically different. Hot water extracts more acidic compounds and bitter oils quickly. Cold water is slower and more selective — it pulls out the sweeter, smoother flavour compounds while leaving a lot of the harsher acids behind. Studies from the University of California found cold brew coffee has significantly lower titratable acidity compared to hot brew, which is why people with sensitive stomachs often tolerate it much better.

That lower acidity also changes the flavour profile entirely. You get more chocolate, caramel, and stone fruit notes. The body is heavier. The finish is longer. If you’ve ever wondered why cold brew from a specialty cafe tastes like a different drink entirely — it’s not just marketing. The chemistry is genuinely different.

One more thing worth knowing: cold brew is typically made as a concentrate. You steep at a high coffee-to-water ratio, then dilute before drinking. This concentrate format means it stores beautifully in the fridge for up to two weeks without going stale.

How to Make Cold Brew Coffee at Home (Step-by-Step)

You don’t need special equipment. A large mason jar, a fine-mesh strainer, and a coffee filter are enough to make a batch that rivals anything you’d buy at a cafe. Here’s the exact process we use at Mumbles, adapted for home brewing.

Step 1 — Choose Your Equipment

A 1-litre mason jar works perfectly for a single batch. If you want more volume, use a large pitcher or a French press (which doubles as a great straining tool). You’ll also need cheesecloth, a fine-mesh strainer, or unbleached paper coffee filters for the final strain.

Avoid using a standard drip coffee maker’s carafe — most aren’t airtight and cold brew needs to be covered throughout steeping.

Step 2 — Grind Your Beans (Coarse)

Grind size is the most misunderstood part of cold brew. Go coarser than you think you need to. You’re looking for something resembling rough sea salt — not espresso powder, not drip coffee, and not Turkish grind.

In my testing at Mumbles, a grind that’s too fine produces a bitter, muddy result that’s nearly impossible to filter cleanly. Too coarse and you get a watery, under-extracted brew. The sweet spot is what specialty roasters call “medium-coarse” — roughly a 7 out of 10 on a standard burr grinder scale.

Use whole beans and grind fresh. Pre-ground coffee absorbs moisture and goes stale quickly; in an 18-hour steep, that staleness comes through.

Step 3 — Measure Your Ratio (1:4 for Concentrate)

The standard cold brew concentrate ratio is 1 part coffee to 4 parts water by weight. If you’re brewing 1 litre, that’s 250g of coffee to 1,000ml of water.

If you prefer a ready-to-drink brew (not a concentrate), move to a 1:8 ratio — 125g of coffee per litre of water. This can be drunk straight over ice without diluting.

At Mumbles, we use a 1:5 ratio for our in-house batch. It produces a concentrate that’s strong enough to hold up over ice but not overwhelming on its own. I’d recommend starting here and adjusting to your preference.

Step 4 — Combine and Saturate

Add your ground coffee to your jar. Pour filtered cold water over the grounds slowly, and stir with a long spoon or chopstick until every pocket of dry coffee is saturated. This step matters — dry pockets in the middle of the jar won’t extract, and you’ll get an uneven result.

Filtered water makes a real difference here. Tap water with heavy chlorination or mineral content changes the flavour more than most people expect. Use filtered or spring water if you can.

Once everything is combined and saturated, seal the container tightly.

Step 5 — Steep (12–24 Hours)

Place your jar in the fridge. Steep for a minimum of 12 hours and no more than 24 hours. Here’s how the timing plays out in practice:

• 12 hours — Light, delicate, lower caffeine. Works well with lighter roast beans.
• 16–18 hours — The sweet spot for most specialty coffee. Full flavour, smooth, well-balanced.
• 20–24 hours — Bold, heavy-bodied, strong. Works with medium-dark roasts. Can become slightly bitter past 22 hours.

We steep our Mumbles cold brew for exactly 18 hours. Every batch. That consistency is what makes it taste the same every time you order it.

You can also steep at room temperature (around 20°C) for 12–14 hours. Room temp extracts faster — but the fridge slows extraction and tends to produce a cleaner, less cloudy result.

Step 6 — Strain Twice

This is where most home brewers cut corners, and it shows. A single pass through a mesh strainer leaves sediment and fine particles in your concentrate. That silt creates a gritty mouthfeel and adds bitterness to every glass.

Strain twice:

1. First pass — Pour through a fine-mesh strainer to remove the bulk of the grounds.
2. Second pass — Run the strained liquid through a paper coffee filter or doubled cheesecloth into your storage container.

Go slowly. Don’t squeeze or press the filter — it forces fine particles through.

If you used a French press, press the plunger slowly, then decant immediately. Leaving cold brew in contact with the pressed grounds will over-extract it.

Step 7 — Store and Serve

Transfer your strained cold brew concentrate into a clean, airtight glass container — a swing-top bottle or mason jar both work well. Store in the fridge.

Shelf life: Cold brew concentrate keeps for up to 14 days when stored properly. Ready-to-drink (diluted) cold brew is best within 7 days.

To serve from concentrate, use a 1:1 ratio — equal parts concentrate and cold water, or substitute the water with oat milk for something richer. Pour over ice and drink immediately.

The Right Coffee Bean, Ratio, and Grind — A Specialty Barista’s View

Equipment and process are secondary to what goes in the jar. Here’s what actually determines the quality of your cold brew.

Which Beans Work Best for Cold Brew?

Not all coffee suits cold brew equally. The extended cold-extraction process amplifies the inherent character of the bean — which is good if you start with quality, and unforgiving if you don’t.

Ethiopian single-origin beans (like our Yirgacheffe lot at Mumbles) produce cold brew with bright stone fruit notes, a natural sweetness, and a floral finish. In my experience, Ethiopian beans make some of the most distinctive cold brew you’ll taste — they don’t need sweetener or milk to be interesting.

Colombian beans tend toward caramel and hazelnut. They’re crowd-pleasing and produce a rounder, fuller-bodied concentrate.

Dark roasts are popular for cold brew because the bold flavour holds up well over ice and dilution. But I’d push back on defaulting to dark. Medium and medium-light roasts carry more complexity — and in cold brew’s slow extraction, those nuances actually survive.

Avoid blends designed for espresso machines. They’re often over-roasted for cold brew’s slower extraction and produce a one-dimensional, smoky result.

Roast Freshness Matters More Than You Think

Use beans roasted within the last two to four weeks. Coffee past four weeks starts losing its soluble compounds — and since cold brew relies on a long, patient extraction, stale coffee produces a flat, hollow result regardless of how long you steep it.

At Mumbles, we roast every Monday in small 6kg batches specifically to avoid this problem. If you’re buying from a supermarket, check the roast date on the bag — not the best-before date.

Quick Reference: Ratio Guide

Style	Coffee	Water	Result
Strong Concentrate	1:4	250g per litre	Dilute before drinking
Standard Concentrate	1:5	200g per litre	Best all-rounder (our ratio)
Ready-to-Drink	1:8	125g per litre	Drink straight over ice

Cold Brew Mistakes That Ruin the Batch

These are the most common errors — most of which I see even in cafes that should know better.

Mistake 1 — Using Pre-Ground Coffee

Pre-ground coffee has been exposed to air since it left the grinder. Oxidation breaks down the aromatic compounds you’re trying to extract. In a 12–18 hour steep, stale grounds produce a dull, flat concentrate with none of the sweetness or complexity you’re paying for. Grind fresh, every time.

Mistake 2 — Grinding Too Fine

Fine grounds create two problems: over-extraction (bitterness) and filtering nightmares. The grounds compact during steeping and clog paper filters, forcing you to wait 30+ minutes for even a partial strain. Coarse grind prevents both.

Mistake 3 — Steeping Too Long

Past 24 hours, even at fridge temperature, cold brew starts to over-extract. The pleasant bitterness that gives cold brew its body tips into harsh, astringent territory. Set a timer when you put it in the fridge. Don’t forget about it.

Mistake 4 — Skipping the Second Strain

A single strain leaves fine coffee particles in suspension. You might not notice them immediately, but after 2–3 days in the fridge, that sediment settles and makes the last few glasses taste gritty and stale. Always do the second pass through a paper filter.

Mistake 5 — Using Warm or Uncovered Water

Room temperature is acceptable for cold brew. Warm water is not — it accelerates extraction unpredictably and can produce a sour, under-developed concentrate. Always keep the container sealed during steeping to prevent the coffee from absorbing fridge odours.

Myth: Cold Brew Has More Caffeine Than Espresso

This one won’t die. Cold brew concentrate is high in caffeine — but once you dilute it for serving (which is how it’s always consumed), the caffeine per cup is roughly comparable to drip coffee. A standard 240ml serving of diluted cold brew sits around 150–200mg of caffeine, similar to a large pour-over. Espresso is more concentrated per ml — but you’re drinking much less of it.

Read More: Best Milk for Coffee — Expert Barista Tips from Mumblescafe.com

FAQs — Cold Brew Coffee

How long should I steep cold brew?

The ideal steep time is 16 to 18 hours in the fridge. This produces a well-balanced concentrate with full flavour and no harsh bitterness. Steeping shorter than 12 hours risks under-extraction; longer than 24 hours can make the brew taste astringent. If you’re steeping at room temperature, aim for 12 to 14 hours.

What’s the best coffee-to-water ratio for cold brew?

For a concentrate, use 1 part coffee to 4 or 5 parts water by weight. At Mumbles, we use a 1:5 ratio — 200g of coffee per litre of water. This produces a concentrate you can dilute 1:1 with water or oat milk. If you want to drink it straight without diluting, use a 1:8 ratio instead.

Can I make cold brew without a special cold brew maker?

Absolutely. A large mason jar, a fine-mesh strainer, and a paper coffee filter are all you need. Many specialty cafes use exactly this setup. Dedicated cold brew makers add convenience but don’t improve quality. A French press works especially well — it simplifies straining considerably.

Why does my cold brew taste bitter?

Bitterness in cold brew usually comes from one of three things: a grind that’s too fine, steeping too long (past 24 hours), or using stale beans. Try coarsening your grind by two or three notches, cutting 2 hours off your steep time, and checking that your beans were roasted within the past month.

Can I make cold brew with dark roast coffee?

Yes — dark roast produces a bold, chocolatey cold brew that holds up well over ice and dilution. That said, medium and medium-light roasts often produce more interesting results because cold brew’s slow extraction preserves delicate flavour notes that heat brewing would destroy. Ethiopian or Colombian single-origin beans at a medium roast tend to be exceptional.

Does cold brew have more caffeine than regular coffee?

Cold brew concentrate is high in caffeine per ml. But since you always dilute it before drinking, the caffeine per serving is comparable to drip coffee — roughly 150 to 200mg per 240ml serving. Espresso has more caffeine per ml but is consumed in much smaller volumes.

How long does cold brew last in the fridge?

Cold brew concentrate stored in an airtight glass container keeps for up to 14 days in the fridge. Ready-to-drink (already diluted) cold brew is best within 7 days. Glass is preferable to plastic — it doesn’t absorb odours and doesn’t leach anything into the concentrate over time.

Should I steep cold brew in the fridge or at room temperature?

Either works. Fridge steeping (12–24 hours) is slower and tends to produce a cleaner, less cloudy concentrate. Room temperature steeping (12–14 hours at around 18–22°C) is faster and extracts slightly more efficiently. Many commercial operations steep at room temperature for 12 hours, then chill. At Mumbles, we use the fridge exclusively for consistency.

Start Your First Batch Tonight

Cold brew coffee is one of the most rewarding things you can make at home. The process is almost entirely hands-off, the results are consistently excellent, and a batch made on Sunday keeps you in great coffee all week.

The variables that matter most — in order — are: fresh beans, coarse grind, correct ratio, and full steep time. Get those right and everything else is adjustable to taste.

If you want to experience what cold brew tastes like when you start with truly exceptional single-origin beans, our 18-hour cold brew is on the menu daily at Mumbles — black or with oat milk, over ice. It’s the same process described in this guide, brewed fresh every morning from our Ethiopian Yirgacheffe lot.

Come in and taste the benchmark. Then go home and brew your own.

Check out our Fitzroy cafe’s cosy workspace — built for deep work and great coffee.