A hot pour-over recipe tastes balanced, so you brew it as usual and pour it over a glass of ice. The first sip is refreshing. A few minutes later, the coffee seems thin.

The ice did more than cool the drink. As it melted, it added water that was missing from your recipe calculation.

Flash brewing plans for that dilution from the beginning. The useful starting point is not a particular number of ice cubes, but three weights: dry coffee, hot brewing water, and ice.

Understand what flash brewing changes

Flash-brewed iced coffee is extracted with hot water, then chilled with ice during or immediately after brewing. It differs from cold brew, where the coffee is extracted using cool water over a longer period. This guide focuses on a pour-over brewed directly into a server containing ice.

You use less hot water than in a comparable hot recipe because some of the total water is reserved as ice. That creates two separate jobs: extracting the coffee in the dripper and cooling and diluting the collected brew. Joe Coffee's flash-brew guide describes this planned dilution and adjusts the brewing recipe accordingly. Joe Coffee's explanation of flash brewing

Simply removing hot water without reconsidering the grind or pouring routine may not produce the same extraction. The iced version needs its own baseline.

Count ice in your total water ratio

For the calculations in this guide:

Total recipe water = hot brewing water + recipe ice

With 20 grams of coffee and a 1:16 coffee-to-total-water ratio, your water allowance is 320 grams. One possible division is 200 grams of hot water and 120 grams of ice.

The coffee-to-hot-water ratio is then 1:10, while the coffee-to-total-water ratio remains 1:16. Neither number is wrong; they describe different things. Always check what a published recipe includes in its ratio.

For example, Counter Culture lists approximately 1:11 plus ice. Its actual quantities are 30 grams of coffee, 335 grams of hot water, and 165 grams of ice. Adding those water quantities gives 500 grams, or approximately 1:16.7 overall. Counter Culture's flash-brew recipe

Example with 20 g coffee	Hot water	Recipe ice	Total water	Overall ratio
More water through the grounds	220 g	100 g	320 g	1:16
Starting example in this guide	200 g	120 g	320 g	1:16
Full hot recipe plus extra ice	320 g	120 g	440 g	1:22

These are arithmetic comparisons, not three equally recommended recipes. The first two preserve total water but change the brewing and cooling conditions. The third shows why adding ice on top of a complete hot recipe can dilute the drink much further.

Do not confuse recipe water with drink weight

A 320-gram water allowance does not promise 320 grams of finished coffee. Some liquid remains in the grounds and filter instead of reaching the server. Barista Hustle distinguishes brewing-water input from beverage weight for precisely this reason. Brew water and beverage weight

Do not automatically add water until the finished drink weighs 320 grams. That would change the recipe, not correct a measuring error.

Ice adds another distinction: any cubes still floating in the server have not yet become liquid dilution. The planned total-water ratio describes the ingredients, not the exact concentration of every sip while ice remains. Record whether your tasting sample contains unmelted ice when comparing batches.

Choose a split that suits your setup

There is no single hot-water-to-ice percentage that works identically with every coffee and brewer. Counter Culture's recipe uses roughly one-third ice; Joe Coffee's published Kalita recipe uses 40%. Those are starting points within complete methods, not universal rules.

Our 200-gram hot-water and 120-gram ice example reserves 37.5% of the total water as ice. Treat it as a practical starting recipe to dial in, not a tested guarantee for your equipment.

Moving some ice weight into the hot-water portion gives you more water to pass through the coffee, but less ice for cooling. Moving the other way increases the cooling allowance while reducing brewing water. The temperature and amount of liquid reaching the server, the vessel, and the ice's starting temperature all affect how much ice melts. Frozen ice does not always start at the same temperature. Barista Hustle on managing ice

Keep the split unchanged for your first few comparisons. It is easier to learn what the grind adjustment does when the dilution plan stays the same.

Brew a measured first batch

Use a pour-over brewer and filter suited to a 20-gram dose, a heat-safe server with room for the drink and ice, a grinder, kettle, scale, and timer. Start with 20 grams of coffee, 200 grams of hot water at approximately 94°C, and 120 grams of ice. A slightly finer grind is also used in Blue Bottle's method, although its dose range and ice allowance differ from this example. Blue Bottle's hot-over-ice guide

1. Prepare the filter first. Rinse it and discard the rinse water before adding your measured ice. Otherwise, the rinse can melt ice and introduce uncounted water.
2. Weigh the ice separately from the brewing water. Put 120 grams of ice in the server. Add the dripper, prepared filter, and ground coffee, then tare the complete assembly to zero. Use your normal pour-over grind or a small adjustment finer as a first comparison.
3. Bloom within the water allowance. Start the timer and pour 50 grams of water, wetting the bed evenly. Allow roughly 30–45 seconds. That 50 grams is part of the 200-gram hot-water total, not an additional amount.
4. Finish the hot-water portion. Pour steadily to a cumulative reading of 110 grams, then continue with another pour to 200 grams as the water level falls. Keep below the brewer's capacity and avoid unnecessarily forceful pouring. Do not tare between pours.
5. Drain, mix, and taste. Record the finish time, remove the dripper, and stir the collected coffee and ice gently. Note whether ice remains. Taste before adding any extra serving ice so you can evaluate the recipe you actually measured.

With the whole assembly on the scale, water moving from the dripper into the server does not count as new weight. Ice melting does not add weight either. The cumulative reading tracks hot water added, approximately, provided nothing is removed or spilled.

Adjust one variable at a time

If the cup tastes pleasant but too light, try a little more coffee while keeping the total water and ice split unchanged. If it tastes weak and lacks flavor, a small move finer is another useful experiment. Kurasu makes this distinction between increasing dose for concentration and changing grind to improve extraction with reduced brewing water. Kurasu's iced-coffee adjustment advice

These are tests, not diagnoses from one sip. A sharp taste alone does not prove under-extraction, and a finer setting is not automatically better. If the brew begins stalling or develops unpleasant dryness, compare a slightly coarser setting or less agitation rather than continuing finer.

If you change the split, exchange equal weights: adding 20 grams of hot water means removing 20 grams of recipe ice to preserve the same total-water ratio. Recheck both taste and cooling afterward.

Keep serving ice consistent

Recipe ice and serving ice have different roles in your notes. The first is already included in the calculation; the second adds further dilution as it melts. Kurasu explicitly notes that coffee served over additional ice changes as those cubes melt. Kurasu on ice and concentration

When comparing recipes, use the same glass, a similar amount of serving ice, and a similar waiting time. Otherwise, a good brewing adjustment can disappear behind a different serving setup.

Keep a short record of dose, hot water, ice, grind, pouring sequence, finish time, and taste. Once the coffee is enjoyable, those measurements give you a recipe you can repeat—not just a cold drink you happened to get right once.