Engineering the Ultimate Boba Milk Tea, Part 3: Ice

This series is a deep dive into the details and thought process behind our boba milk tea at Camellia Rd Tea Bar.

Here in Part 3, we're going to talk about ice. Expect to learn how ice affects a boba milk tea drink in terms of its temperature, its taste, and overall enjoyment of a drink.

Drink Temperature

Temperature affects our food and beverage experience psychologically and physically.*

1) Psychologically, iced drinks are more associated with sweets and refreshments (ice cream, "ice cold beer", etc). Hot drinks are more associated with comfort or nourishment (morning cup of hot coffee, soup, etc). These associations aren’t universal, and social norms have a big part to play in this. Here in sunny San Diego, we generally prefer iced cold drinks.

But what is the perfect temperature? It's subjective, but at Camellia Rd Tea Bar we think that the first sip should be cold, but not necessarily ice cold ("brain freeze" isn't fun). The ideal temperature would be “refrigerator” temperature,  ~35°F to 38°F.

2) Physically, colder foods and beverages can actually dampen our experience of flavors. As an example, warmed up and melted ice cream will taste sweeter than ice cream cold and straight out of the freezer. At Camellia Rd Tea Bar, we want our cold drinks to still be full of flavor and craft our recipes accordingly. For example, for our Hong Kong Milk Tea, we add slightly more sugar to our cold version than our hot version to account for this difference in sweetness perception due to temperature.

Thermal equilibrium

Ice is the standard way to keep drinks cold in a convenient and cost-effective way over an extended period of time near the ideal temperature range.

Some quick chemistry on water:

Temperature is a measurement that reflects the average amount of energy in a substance or system. When water gets colder, there is less energy. When energy is low enough, the water molecules stop “moving around so much” (less kinetic energy in the system) and hydrogen bonds form between water molecules as they settle into a repeating, lattice structure. This is what happens when water changes phases from a liquid into a solid.Conversely, ice keeps a drink cold by absorbing energy from the drink liquid and does so via contact with the drink. When ice absorbs energy, the hydrogen bonds break, freeing the water molecules from the structure and results in water changing phases from a solid into a liquid. We want our boba milk tea drinks to be cold and refreshing, but melting ice poses an issue for long term drink quality as melted ice water dilutes a drink over time.

We find that melting ice can, in some cases, add to the drink experience. For example, a Vietnamese-style iced Cà Phê Sữa Đá coffee can be incredibly strong and sweet for those first sips. But as the ice melts, it can mellow out the drink and prevent it from being overwhelming.

At Camellia Rd, our drinks are typically stronger and more tea-forward in flavor, and we also want that first sip to showcase that. We don't like to pour hot or warm tea over ice to rapidly cool it down (we've found it to be less flavorful). Instead, we pre-chill our tea bases and either keep them in a fridge or an insulated dispenser so that the tea is already cold before we prepare a drink. This is a small detail that helps minimize initial dilution.

Ice

In this next section, we’ll talk about ice and how we considered different variables, including the volume (total amount), surface area (a product of size and shape), and quality (purity).

Volume

At Camellia Rd Tea Bar, we use an average of about 3 fl oz of ice for our drinks. We've found this to be a great amount to be able to keep drinks cold over an hour, without over diluting the drink. This volume of ice can vary depending on the specific drink; for a stronger or layered drink, we tend to use more.

We've also found that a lot of other cafes and shops prefer to keep their drinks extra cold over an extended period of time by using a lot more ice. For example, we've seen one boba tea chain use over 12 fl oz of ice in their extra large 32 fl oz cup. However, we feel like this just overwhelmed the drink experience.

Surface area

Certain shapes have a higher surface area than others. Geometrically, if we're given a perfect ice cube and a perfect ice sphere with equal volume, then the ice cube would have larger surface area. Additionally, ice that's broken up, has holes, or smaller will have more surface area then ice that's larger and not broken up.

As we discussed above, more ice surface area -> more contact with drink liquid -> faster rate of ice melting. We want some to occur to keep the drink cold, but not so much that it makes the hurts the drink taste.

As a rough illustration, if we compare the 2-D ice cube on the left to the nine "cut up" ice cubes on the right, the total perimeter of the nine ice cubes on the right is 3x the perimeter of the single large ice cube.

There are also operational limitations to the what we can do at Camellia Rd Tea Bar. For example, a single large Kuramoto ice cube is great for cocktails for its aesthetic and minimal surface area, but it wouldn't be practical for a quick-service boba tea shop in terms of cost and availability.

Ice Quality

The last important variable is with the ice quality itself. Like most cafes, we have an in-house commercial ice machine that's connected to the water line and produces ice constantly. This water is run through water filters, so that the ice that is produced is clear, clean, and doesn't impart unwanted mineral or other flavors into the drink.

Here’s a graphic on commercial ice:

Graphic via webstaurant.com*

Conclusion

At Camellia Rd Tea Bar, we use crescent (half moon) shaped ice. The ice distributes well for layering drinks and easy mixing. It also doesn't melt too quickly and all in all it's a great balance in terms of its size, surface area, and form. We also use a relatively lower volume than most shops; enough to keep a drink cold but not overwhelm the cup.

Thanks for reading! Hope you found this interesting. Part 4 will be on sweeteners.

-Ricky

P.S. Personally, I actually love small, crushed pebble ice for certain drinks - I like how cold it makes the drink and to be able to chew on the ice. However, this is actually one of the fastest melting types of ice and sadly biting on ice isn't a great habit to have.

*Articles on temperature & taste:

https://www.fishersci.com/us/en/scientific-products/publications/online-exclusives/taste-smell-temperature-the-key-ingredients-flavor.html

https://www.ncbi.nlm.nih.gov/books/NBK236241/

**Commercial Ice: https://www.webstaurantstore.com/article/380/types-of-ice.html?srsltid=AfmBOopnopmgR6gre_kietvEcTcBkWOH3-BmMbctAM6VKnlzHSwMe5hw