Ngọt như đường cát, mát như đường phèn.
Sweet as sand sugar (refined sugar), cool as rock sugar.
– old folk saying
Known in English as rock sugar or even rock candy, đường phèn can be white or golden. The second time I returned to Canada from Việt Nam, my mother-in-law packed a big bag of đường phèn for me to take along. She told me to use it to make chè (sweet soupy desserts) with the fresh lotus seeds that she’d already stuffed into my baggage. It’s also one of the secret ingredients for making a phở broth beyond the ordinary. My husband’s gradmother, whom we call Mệ, likes to nibble on chunks of rock sugar while sipping strong green tea. This sugar is a specialty of Quảng Ngãi province, a major sugar cane-growing region. Rock sugar is traditionally a popular gift for close friends or family, especially if they are setting out on a trip.
I insisted I didn’t need it, because I didn’t know what else to use it for, and I was going to return to Việt Nam in a few months. She said she’d bought it just for me, and so, despite all the extra weight it added to my bags, I accepted her gift. It took me a while to learn how to appreciate rock sugar. The first time I pounded some with a pestle to break it into powder, I saw sugarcane fibers threaded amongst the crystals and thought they were impurities from the bags they’d been packaged in for bringing to the market. My mother-in-law snickered when she saw me trying to pick them out. “No, no! Those are cane fibers. They won’t hurt you.”
She usually buys regular, white refined sugar, or đường cát trắng. The crystals are a little larger than we are used to in the West, so it doesn’t dissolve quite as readily, but the taste is almost the same. Because it’s refined, it has no (or few) impurities and it’s what you’ll get with your iced black coffee and what most Vietnamese cooks use at home. My mother-in-law says the rock sugar is special and she rarely buys it, but she remembers that when she was small, refined sugar was expensive and cherished, while rock sugar was looked down upon.
Rock sugar still has the delicate, smoky flavour from the cane, which is why it’s so good in phở. It’s not a flavour you can pin down; just a mysterious “something”. It works for Huế Beef Noodle soup and for other soups too.
I use đường phèn whenever I need caramelized sugar for a dish. It melts and caramelizes quickly, whereas refined sugar seems to take forever. I’ve even had it refuse to caramelize at all. Đường phèn comes through for me every time. And then there’s that wonderful flavour. I take the sugar off the heat while it’s still golden and it continues to darken a little more, but not so much as to lose that flavour.I use the caramelized sugar most often for making “kho” dishes; foods that are finished in a fish sauce and caramel mixture. Once in a while, I use it for flans (crème caramel).
If using Vietnamese rock sugar to make chè, the sugar can be dissolved and filtered first, to remove the cane fibers. For “kho” dishes and for soups, this isn’t necessary. In the West, rock sugar can be purchased from most Asian markets. Don’t confuse it with the brown or golden discs of palm sugar. (These are made from Toddy Palms, and have a different flavour.) The sugar I get from the market in Huế comes in jagged chunks roughly the size of golfballs, but I’ve seen it sold as smooth grape-sized pieces in Montreal’s Chinatown. This sugar appears to be harder, drier and almost transparent compared to the one I’ve been using. I’ve never tried it though, as I’ve never run out of what I bring back from Việt Nam.