A couple months ago, my mom made 화채 (Hwachae), a Korean punch-sorta-thing. Normally, it’s made by putting watermelon, Korean melon, and etc. in 7-up. But apparently the trendy thing in Korea is to put milk in it too. So my mom put together watermelon, Korean melon, peach (or nectarine?), kiwi in 2:1 7-Up/milk solution. When she made it, everything tasted good… but a few hours later, it got REALLY bitter. What the heck? Wondering what could be wrong, I devised this experiment to get to investigate.
1) 7-Up/Milk Solution (control)
2) 7-Up/Milk + Watermelon
3) 7-Up/Milk + Korean melon
4) 7-Up/Milk + Peach
5) 7-Up/Milk + Kiwi
By figuring out which of these samples turn bitter, I would know which fruit was responsible for turning my mom’s 화채 (hwachae) bitter. If it was the mixture of 7-Up and Milk that turns bitter, then all the samples would become bitter. For this I (safely) assumed that milk by itself and 7-Up by itself are not bitter.
After making each sample (about 2:1 7-Up/Milk ratio; fruit mass not standardized due to laziness), I tested each sample. None of the samples tasted bitter immediately after creation.
I covered each sample with saran-wrap (to avoid spillage) and stored in the refrigerator for roughly 24 hours. The exact temperature of the fridge was not recorded because this isn’t exactly supposed to be high-quality science (plus I was lazy). The samples were taste-tested by 4 people (me, Mom, Grandma, and Grandpa).
[Initial Taste] None of the samples were bitter.
[Observation] Within a few minutes (while making other samples) some of the samples developed white yucky substances.
1) 7-UP/Milk (control) – Tasted fine. Developed some white yucky substances though.
2) 7-Up/Milk + Watermelon – Tasted fine. No white yucky substances.
3) 7-Up/Milk + Korean melon – Tasted fine. No white yucky substance.
4) 7-Up/Milk + Nectarine – Tasted fine. Mom thought it tasted slightly bitter, but the rest of the investigators (Grandma, Grandpa, and I) think she cray-cray. Slight white yucky substances development.
5) 7-Up/Milk + Kiwi – Tasted bitter to everyone. Lots of white yucky substances.
The Kiwi sample was the only bitter one after 24 hours, so I conclude that Kiwi was the culprit. It is unclear whether it’s the 7-Up + Milk + Kiwi combination or some Kiwi-containing subcombination that is responsible for the bitter flavor though. Also, it is not impossible that the pervasive white yucky substance is related to the bitterness. However, it is interesting that the 7-Up/Milk-only sample developed some of the white yucky substance whereas the 7-Up/Milk+Watermelon and 7-Up/Milk+Korean melon samples did not develop any. Perhaps something in the melons counteract the 7-Up/Milk reaction? What is this white yucky substance?
Lastly, it may be worth making a 화채 (Hwachae) with all of the above ingredients sans Kiwi, to firmly conclude that the Kiwi was the sole culprit. And are there other fruits that have the same hwachae-bittering effect as Kiwi? What is the chemistry behind this?
I want to thank Mom, Grandma, and Grandpa for helping with the final taste tests. Also Mom deserves credit for cutting the fruits and purchasing some of the ingredients.