How We Brew Cold Brew at mumblescafe.com — Expert Guide

Most cafes pour cold brew from a bag. We don’t.

Every batch of cold brew at mumblescafe.com is made in-house, steeped for exactly 18 hours, and served within 48 hours of brewing. Nothing pre-made, nothing from a supplier, nothing sitting in a fridge for a week.

Cold brew is one of the most misunderstood drinks in Melbourne’s cafe scene. People think it is just iced coffee. It is not. The difference in taste, caffeine, and acidity is significant — and once you understand it, you will never go back to iced coffee again.

This guide covers exactly how we make cold brew at mumblescafe.com, why we make it this way, what it does to the flavour, and how you can replicate a version at home.

How does mumblescafe.com brew cold brew coffee?

Cold brew at mumblescafe.com uses coarsely ground single-origin beans steeped in cold filtered water for 18 hours at 4°C. No heat is involved at any stage. The result is a smooth, low-acid concentrate served over ice — black or with oat milk.

• Beans: Ethiopian Yirgacheffe or Colombia Huila — single origin, roasted within the week
• Grind: Coarse — similar to French press grind size
• Water: Filtered cold water at 4°C — refrigerator temperature
• Ratio: 1 part coffee to 8 parts water — produces a concentrate
• Steep time: Exactly 18 hours — not 12, not 24
• Serve: Over ice, black or with oat milk — never diluted before serving

What is Cold Brew and Why Does It Taste Different?

Cold brew is not iced coffee. This is the single most important thing to understand before anything else.

Iced coffee is hot espresso poured over ice — the heat extracts the coffee quickly, the ice melts into it, and you end up with a diluted, often bitter drink. Cold brew uses no heat at all. Cold water extracts the coffee slowly over many hours, producing a completely different flavour profile.

The science behind it is straightforward. Heat extraction pulls compounds from coffee quickly — including acids and bitter-tasting oils. Cold extraction is slower and more selective. It pulls the sweeter, smoother compounds first and leaves behind much of the acidity and bitterness.

The result is a drink that is naturally sweet, smooth, and significantly lower in acid than any hot-brewed coffee. For people with sensitive stomachs who struggle with regular coffee, cold brew is often the answer.

Key difference — cold brew vs iced coffee:

Cold brew is steeped in cold water for 12–24 hours with no heat involved. Iced coffee is hot espresso or filter coffee served over ice. Cold brew has lower acidity, higher caffeine concentration, and a smoother, naturally sweeter flavour. Iced coffee is faster to make but significantly more bitter and acidic by comparison.

How We Make Cold Brew at mumblescafe.com — Step by Step

We developed our cold brew method over two years of testing different ratios, steep times, bean varieties, and grind sizes. What we use today is the result of dozens of batches — not a recipe we found online.

Step 1 — Bean Selection

We only use single-origin beans roasted within the past seven days. Currently our cold brew runs on the Ethiopia Yirgacheffe lot — its natural sweetness and low bitterness respond exceptionally well to cold extraction. When the Colombia Huila seasonal lot is available, we run a side batch for comparison.

Stale beans produce flat, lifeless cold brew. This is why most cafe cold brew disappoints — it is made with commodity beans that have been sitting in a hopper for weeks.

Step 2 — Grind Size

We grind coarse — approximately the same setting as a French press. This matters more than most people realise. Too fine and the cold brew over-extracts even at low temperatures, producing bitterness. Too coarse and you get weak, watery results with no body.

In my testing across different grind settings, a coarse grind at 18 hours produces the cleanest cup. A medium grind at the same time produces noticeable astringency. The grind size is not negotiable.

Step 3 — Water Quality

We use filtered water only. Melbourne tap water is perfectly safe to drink but contains chlorine compounds that affect coffee flavour noticeably — especially in a drink where no heat is used to dissipate them. Filtered water produces a cleaner, brighter cold brew every time.

Temperature at the start of steeping matters too. We begin with water at 4°C straight from the refrigerator. Room temperature water speeds up extraction unpredictably and can produce inconsistent results batch to batch.

Step 4 — The Ratio

Our ratio is 1 part coarsely ground coffee to 8 parts cold filtered water by weight. This produces a concentrate — not a drink-ready brew. When served, we pour it directly over ice without diluting. The melting ice brings it to the right drinking strength naturally.

Some cafes use a 1:4 or 1:5 ratio for a stronger concentrate that they dilute with water before serving. We prefer 1:8 because it gives the customer a truer representation of the bean’s flavour without requiring us to dilute anything ourselves.

Step 5 — 18 Hours Steep

Every batch goes into the refrigerator at 4°C for exactly 18 hours. We have tested 12 hours — the extraction is incomplete, the sweetness is there but the body is thin. We have tested 24 hours — the extraction tips into over-extraction territory, adding unwanted bitterness. Eighteen hours is the sweet spot for our current beans and grind setting.

Our head barista Sarah Lin checks every batch before it goes on service. If the colour is too light or the taste profile is off, it does not go out. This happens rarely — but it has happened, and we throw the batch rather than serve it.

Step 6 — Filtering

After 18 hours, we filter the brew through a fine mesh filter followed by a paper filter. Double filtration removes all sediment and produces a crystal-clear, clean cold brew. Single filtration often leaves fine particles that make the drink cloudy and slightly gritty.

Step 7 — Service Window

We serve cold brew within 48 hours of brewing. After 48 hours, oxidation begins to affect the flavour — particularly the brighter fruit notes from our Ethiopian beans. Any batch not fully served within the window is discarded.

This is why we sometimes run out of cold brew before closing time. We would rather run out than serve a batch that is past its best.

What the 18-Hour Steep Actually Does to Flavour

The steep time is the most important variable in cold brew production. Most people focus on the bean or the ratio — but time is what separates a great cold brew from a mediocre one.

At 12 hours, the extraction is around 60–70% complete. You get the sweetness and some of the fruit notes but the body is underdeveloped. It tastes thin and one-dimensional.

At 18 hours, extraction hits approximately 85–90% of what cold water can pull from the grounds. The sweetness is fully developed, the body is present, and the fruit or floral notes — depending on the bean — are clearly defined.

At 24 hours, extraction continues past the optimal point. Bitter compounds that cold water extracts slowly start to accumulate noticeably. The drink becomes heavier and harder to finish.

Our head barista Sarah describes the difference clearly: “The 18-hour mark is where the bean’s personality shows up fully without the harsh notes that come from pushing too long. With the Yirgacheffe, you get blueberry and dark chocolate at 18 hours. At 24, those notes flatten and a woody bitterness takes over.”

Caffeine in cold brew vs espresso:

A standard 250ml serve of our cold brew contains approximately 150–200mg of caffeine — higher than a double espresso because of the longer contact time between water and grounds. Cold brew is a genuinely high-caffeine drink. If you are sensitive to caffeine, one glass is enough.

Common Cold Brew Mistakes and Myths

Mistake 1 — Using fresh-roasted beans (within 3 days of roast)

Beans need to degas after roasting. Beans roasted within 2–3 days release CO2 that interferes with cold extraction, producing an uneven and often flat brew. We wait at least 5–7 days after roast before using beans for cold brew. Counterintuitively, beans that are too fresh make worse cold brew.

Mistake 2 — Steeping at room temperature

Room temperature cold brew — sometimes called “ambient brew” — extracts faster and less cleanly than refrigerator-temperature brew. The risk of bacterial growth also increases significantly at room temperature during a long steep. Always steep in the refrigerator at 4°C.

Mistake 3 — Using the wrong grind

This is the most common home cold brew mistake. A medium or fine grind at 18 hours will over-extract badly in cold water. Use a coarse grind — if you have a grinder at home, set it to French press or coarser.

Mistake 4 — Thinking cold brew is just strong iced coffee

Cold brew is a different drink entirely. It is not stronger in the sense of being more bitter — it is smoother and sweeter than any hot-brewed coffee. The higher caffeine comes from longer contact time, not from roast level or intensity.

Myth — Cold brew has less caffeine because it uses cold water

False. Cold water extracts caffeine efficiently over time. A 250ml serve of cold brew typically contains more caffeine than a double espresso — roughly 150–200mg compared to 120–160mg. The cold temperature slows extraction but the 18-hour steep compensates fully.

Myth — All cold brew tastes the same

Completely wrong. Bean origin, roast level, grind size, ratio, and steep time all produce dramatically different results. Our Ethiopian Yirgacheffe cold brew tastes nothing like a cold brew made from a dark-roasted commodity bean. Single-origin cold brew showcases the bean — commodity cold brew hides it.

Read More: Espresso vs Long Black — Complete Guide | Mumblescafe.com

FAQs

Q: What is cold brew coffee and how is it made?
Cold brew is made by steeping coarsely ground coffee in cold filtered water for 12–24 hours with no heat involved. The result is a smooth, low-acid concentrate served over ice. mumblescafe.com steeps every batch for exactly 18 hours at 4°C using single-origin Ethiopian beans roasted within the week.

Q: Is cold brew stronger than espresso?
Cold brew contains more total caffeine than a double espresso — approximately 150–200mg per 250ml serve versus 120–160mg for a double shot. However, cold brew tastes smoother and less intense than espresso because it lacks the bitter compounds that heat extraction produces. More caffeine does not mean more bitterness.

Q: How long should cold brew steep?
Between 12 and 24 hours depending on your ratio and grind size. At mumblescafe.com, we steep for exactly 18 hours using a coarse grind and a 1:8 coffee to water ratio. Twelve hours produces thin results. Twenty-four hours risks over-extraction and bitterness. Eighteen hours is the sweet spot for single-origin beans.

Q: Is cold brew less acidic than regular coffee?
Yes — significantly. Cold water extraction pulls far fewer acidic compounds than hot water extraction. Cold brew typically measures pH 6.3 compared to pH 5.0 for hot brewed coffee. This makes cold brew a better option for people with acid reflux, sensitive stomachs, or those who find regular coffee too harsh.

Q: Can I add milk to cold brew?
Yes. At mumblescafe.com we offer cold brew black over ice or with oat milk. Oat milk works particularly well with cold brew because its natural sweetness complements the smooth, low-acid profile without overwhelming the bean’s flavour. Whole milk and almond milk both work too — it comes down to personal preference.

Q: How long does cold brew last in the fridge?
Filtered, properly sealed cold brew lasts up to 10–14 days refrigerated. At mumblescafe.com we serve every batch within 48 hours of brewing for peak flavour. After 48 hours, oxidation begins to flatten the brighter fruit notes — the drink is still safe to consume but noticeably less interesting.

Q: What beans are best for cold brew?
Light to medium roast single-origin beans work best for cold brew. The slow cold extraction amplifies sweetness and fruit notes — qualities that shine in lighter roasts. Dark roasts become flat and bitter in cold brew because their dominant flavour compounds are the first to over-extract. At mumblescafe.com, Ethiopian Yirgacheffe is our cold brew bean of choice.

Conclusion

Cold brew is one of the most rewarding coffee drinks to understand — and one of the most disappointing when it is made badly.

What separates our cold brew at mumblescafe.com from most versions in Melbourne is simple. We use beans roasted within the week. We grind fresh for every batch. We steep for exactly 18 hours at 4°C. We filter twice. And we serve within 48 hours.

None of these steps are shortcuts. All of them show up in the glass.

Next time you visit mumblescafe.com at 123 High Street Fitzroy, order the cold brew black over ice. Ask your barista what the current bean is. Take your first sip without rushing it. You will taste exactly what 18 hours of patient extraction produces.

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