Jiangzhuangnai, little ginger milk puddings

Jiangzhuang Nai. When I picked up a small bowl of “white pudding,” possibly at one of those lavish breakfast buffets in Beijing the time I went to do a training for Schlumberger–or perhaps it was Hong Kong for that mixed class?–but either way, I had no idea what I was about to taste, nor that this gingery little milk pudding is called Jiangzhuangnai or Jiangzhinai, nor that it’s an old snack of the Pearl River Delta–“Guangzhou’s Shawan town of Panyu district, a town flowing with milk and honey“–its origins in southern China. Cool, with a warming ginger spice kick and only very lightly sweetened as most Chinese sweet things are, this was an unusually pleasant surprise. I lost no time in asking about it, and finding that it was made by simply combining warmed, sweetened milk with ginger juice in a specific manner. The curdle would be immediate, the jiangzhinai ready in moments, or chilled and served some hours later. A chef’s easiest dessert. A restaurant owner’s cash cow (& god-help-me, a welcome alternative to those ubiquitous, boring crème caramels). The very thing to satisfy all those non-sweet-toothers. Not vegan, but eggless & downright delicious.

I read around a little, and made it. The milk needs to be sweetened to taste first and brought to curd-setting temperature, warm to the touch but not hot. Grating and squeezing the ginger juice takes the longest, because you get barely drops for grating inches. But you don’t need much for each pudding, so there’s a consolation. The ginger juice gets distributed among the bowls in which the jiangzhinai is to set, just about a 1/4 teaspoon or 5-6 drops in each or the ginger taste gets too sharp. The pour needs to be from a decent height so that the ginger juice mixes naturally with the warm milk, like a waterfall churning the soil at the point of its fall. No further stirring. This is essential or the pudding gets ruined before it’s made. Leave it out for 15, leave it in a fridge for 30, and the puddings are ready. Can it get any easier?

If your brain works even a little bit like mine, you’re thinking already of jiangzhinai as a great little dessert to make for a crowd –or, even better, with kids, a way to teach them of the kitchen as a lab testing space and a bit about everyday culinary chemistry. Why does the ginger juice need to be freshly squeezed? Why does the temperature of the milk need to be just-so? Why the tall pour–and what happens really that the milk becomes this we pudding in barely moments? Could we add some other juice and achieve some similar effects?

The science of the jiangzhinai

Turns out, what’s happening with jiangzhinai is milk coagulation. Milk proteins are hydrophillic, structurally with “tails” that suspend them in the milk. When ginger juice gets added at an optimally warm temperature, the ginger proteases, or enzymes naturally occurring in ginger, snip the “tails” of these milk proteins and cause them to cluster–a process we know and see as coagulation, but what is scientifically proteolysis, the denaturing of the the main milk phosphoprotein, casein. The result is a clump of milk proteins and the associated whey–the water they can no longer be dissolved in, separated to one degree or another. The specific protease responsible: zingibain, which was first reported as a new source of protease in 1973, by Japanese researchers. And in this case the whey separation is not so pronounced as it might be with the addition of an acid like lime juice (as in paneer or fresh cheese making), so the result is a relatively soft pudding cup which releases whey as you come at it with a spoon.

There’s a difference between fermenting milk and coagulating, worth noting for the record, since they sometimes work in tandem. The work of bacteria acting on the lactose in milk is fermentation; among the bacteria we prefer are Lactobacillus, Lactococcus lactis, Leuconostoc, Streptococcus thermophilus–the kinds that produce yogurts or clabbers raw milk & gets us sour creams, or what the South Africans call maas or amasi. Fresh, raw milk is naturally rich in these bacteria and will never, it’s commonly said spoil, but only will ferment. Of course, the fattiness of the milk, the combinations of natural bacteria present, the ambient temperatures all can affect outcomes. But, free of other contaminants, clean, fresh milk should only sour, not spoil. Factory processed pasteurized milks, by contrast, are deliberately stripped of their natural flora and remain bare to the action of the bacteria that work on milk proteins instead–producing odors, ruining taste, and effectively “spoiling” milk.

Enzymatic action is different though it acts on those very proteins. Very technically, however, enzymatic coagulation produces cheese, so jiangzhinai is very properly a soft cheese though its character is more that of a “sweet pudding.” Ginger as a source of zingibain is the choice for jiangzhinai, but milk can be coagulated with the juices of (or rather, enzymes present in) kiwi juice, pineapple, and even papaya–though you’ll have to test and see what produces the most suitably pleasant tastes.

Chinese Royal cheese or gua-nai, an old dairy product now popular in China, is made from milk coagulated with glutinous rice wine–but the rice wine itself is produced via methods of fermentation: “Traditionally, glutinous rice wine is made through fermentation by inoculating steamed glutinous rice with commercial starter (chiu-yao) or fungal cultures, and the filtrate liquid of glutinous rice wine, in which the rice is thrown away, has been used as both milk-clotting agents and flavoring agents to produce Gua-nai.” Other research has shown that “that the milk-clotting of glutinous rice wine was a special process of chemical catalysts by rennet-like protease, an acid protease produced by molds of rice starter during glutinous rice fermentation. Therefore, the coagulation of Chinese Royal cheese is a kind of enzymatic coagulation.” [Source]

These traditional coagulation and cheese-making practices have gained interest, largely because of the increasing price of rennet–a set of enzymes produced in the stomachs of ruminant mammals–its accessibility and ethical concerns over its production and use. As with rice wine, so with ginger, which has been widely evaluated as a possible rennet substitute and coagulant in the cheese making industry [see this article, for instance].

Proteases are worthy of a whole set of other investigations since they’re critical to the efficacy of the so-called “probiotic” cleaning agents that everyone and their sister is trying to manufacture out of citrus, papaya peels and such. What we produce by fermenting citrus peels might be vinegar, but is not necessarily either enzymatic or “probiotic” (whatever that means, in a cleaning context) at all. More on that in a subsequent post, possibly.

In the meantime, it’s of interest also to note that the market in proteases, ginger proteases included, is tremendous, with applications in the detergent, leather, silver recovery, dairy, baking, beverages/breweries and pharmaceutical industries. Plus, if you’ve ever used raw papaya to tenderize lamb or found that a meat marinated with ginger-garlic paste is so much more tender than one done without — then you’ve used proteases to hydrolyze muscle and tissue proteins yourself, and you know something of their home and commercial value.

Back to jiangzhinai. To design an experiment, consider its variables:

• Protease source: ginger, but also pineapple, kiwi, papaya, and even rice wine, each with its own protease variant. Change these around, see what works? You could also play with fresh/new ginger vs. old ginger and see what produces better results. Which produces a harder set? Which tastes better?
• Milk protein content: Milk with lower protein content produces a softer curd, milk with higher protein produces a “harder” curd.” The ginger proteases snip more tails, produce more clumping.
• Milk temperature: The warmer the temperature, the harder the set, but there is an optimal range. Below 40°C, there’s no coagulation or the coagulation happens much too slowly and incompletely for a pudding to set. Too much higher than 70°C, the protease itself gets denatured and unable to act. This is also why you want to boil ginger with water first while making ginger tea, adding milk later. Add milk too soon, and it’ll merely “break,” destroying your chai.
• Milk clotting is affected by other factors, too: pH, ionic strength, enzyme concentration, and metal ions. But the protease source, protein content, and milk temperature should be good enough and plenty to work with for a household science project with your little ones.

So then, pick one variable, and play with it.

• Keep the milk temperature stable and add new and old ginger juices, papaya juice, kiwi juice, and pineapple juice (all fresh!) & see what happens with each.
• Use skimmed milk and whole fat milk and just ginger juice
• Use hot milk, warm milk, and cool milk for a Goldilocks test.
• and so on…

Document your findings, take a picture and share with me if you try!