• Nishchay Nath

Flash-chilling: Optimal ice-to-water ratio in coffees

Ice is added to drinks to make them cool. But there are 2 challenges here. Adding less ice can lead to a warmer drink than expected, whereas adding more ice can lead to watering down of the drink as the ice melts. To beat this, I looked up a few videos on how much ice is added to flash chill brewed coffee. I came across a lot of opinions on the matter ranging from 30% to 50% ice to water. So I thought of running an experiment on this to get the coolest possible drink, create a standard out of it and subsequently the brewing parameters.


Objective: Find the optimal ice-to-water ratio to cool drinks


Equipment:

  • Glasses

  • Temperature scale

  • Weighing scale

  • Timer


Method: Time vs. temperature study at 30%, 40%, 50% and 60% V/V ice-to-water


Steps:

1. Added 60 gms ice to 140 gms water and start the timer

2. Noted the temperature at 5 second intervals

3. I was constantly stirring to ensure consistent cooling of the entire ice-water mixture

3. Took the readings for up to 150 seconds or until the curve plateaued

4. Repeated the experiment for 40%, 50% and 60% ice-to-water ratios


Results:

The following results were obtained


Before I make my observations, there are certain points to note here specifically the sources of error.

  • Readings may not be accurate because I used a pretty generic temperature gauge which was analog and not digital (need to invest in a better quality one soon!)

  • As per the laws of thermodynamics, all the ice should melt at ~27.3% V/V ice to water and the final temperature of the 0°C. But this is not the case since other forms of loss such as through radiation and conduction are not accounted for plus errors due to the gauge's conductivity itself

  • In a perfect condition i.e. measurements taken ad infinitum, the temperature may have stabilised around a much lower temperature than reported here

  • Coffee will alter the thermal conductivity of water and this exercise has to be taken for an approximation (Starting to question the relevance of this experiment? Fret not! 1°C margin of error will not alter the taste much)

My observations:

  • 30 seconds to 1 minute is a great time to target a drink's temperature. On that basis, I found 40%+ to be a minimum required volumetric ratio

  • In my opinion, there are 2 sets of temperatures i.e. one that is great for a super chilled drink (1°C to 2°C) and other which is best to enjoy the complexity of the coffee (3°C to 6°C)

  • 60% V/V ice-to-water gets chilled pretty fast and may be the ratio to target if you love icy drinks. I target 60% and tweak the brew ratio accordingly on the days I want to enjoy a darker roast in super chilled fashion

  • 40% and 50% V/V ice-to-water gives you temperatures in the 3°C to 6°C bracket, making it ideal for enjoying those flash-chilled pour overs and AeroPresses

  • 50% V/V ice-to-water remain colder for a longer duration in the 3°C to 6°C bracket and should be preferred for iced brews


Important note: As you tweak the ice-to-water ratio, you need to tweak the brew ratio as well. Say you are targeting the Golden ratio of 1:16.67 and a 40% V/V ice-to-water ratio, then the brew ratio changes to 1:10 by shaving the 40% of 16.67 off the brew ratio. So for a 20 gm coffee, you use 200 ml water to brew and then pour the extract over 133 ml of ice.


Final take

I love the 50% V/V ice-to-water. I enjoy a colder flash chilled coffee and this ratio allows me to get the best of flavours as well.


Lastly, this is my personal. You may choose to brew at whatever ratio suits you best. Make it a double shot of espresso on the rocks if that's your jam!


Happy brewing!