Not long ago I was surprised and pleased to find myself, my new book (The Rye Baker) and this blog mentioned in a Washington Post food article titled “Why are some rye breads scalded?” By way of defining a scald, the author posted a link to the British blog Virtuous Bread that describes the how-tos of scalding and concludes – rightly so – that the technique produces a “gorgeous bread” with a crumb that’s “soft and chewy as if there was a lot of fat in it.”
From my point of view, the article was a very good start, but only part of a more complex and nuanced story.
As a physical process, scalding is nothing more than soaking milled grain in near-boiling water and letting it stand for a period of time in either a heated or unheated environment. Time and temperature bring about a series of physical and chemical changes that depend on whether the flour is refined or wholegrain and which influence the taste and/or texture of the finished loaf.
Scalding milled whole grains – the method I use most frequently – influences the chemistry of dough fermentation and the flavor profile of my breads. In a nutshell, three elements influence dough chemistry: the amylase enzymes that convert starches to sugars, the yeast that convert those sugars into alcohol and CO2 and the lactobacilli (LAB) that convert sugars into the lactic and acetic acids that give sourdough breads their characteristic tang.
Each of those three elements has a different temperature/activity curve. Yeast is most active at around 82°F/28°C and LAB at about 90°F/32°C. Both yeast and LAB are living organisms that can’t survive at temperatures above 140°F/60°C. Amylase enzyme activity, on the other hand, peaks in the range of 140-170°F/60-77°C and grinds to a halt above 175°F/80°C. Many of the scalded breads I bake call for keeping the scald at a “sweet spot” of 160°F/70°C for anywhere from three to 18 hours; others allow the scald to return gradually to room temperature.
What this means in practical terms is that scalding milled whole grain, which is rich in natural amylase, effectively kills both the yeast and LAB present in the grain and creates an ideal environment for the conversion of starches to sugars. The sugar-rich scald both provides a nutritional boost to both the yeast and LAB that ferment the final dough and also produce the subtle play of sweet and sour typical of Russian and Baltic rye breads.
I’ve already written about several rye breads that use scalds to control enzyme and fermentation activity, specifically Deconstructed Saison Rye, Black Rye Bread and Moscow Rye, and over time will almost certainly post lots more.
The second type of scald the one that Virtuous Bread describes – is tangzhong (湯種) — which translates as “boiled roux” — a Chinese technique for scalding refined flours that has become common throughout Asia, most notably as a major component of Hokkaido Milk Bread, and is now being widely adopted by Western bakers.
Simply stated, making a tangzhong entails combining about a third of a bread’s total flour with five times its weight in liquid, typically water or milk, and heating the mixture to a temperature of 150°F/65°C. The tangzhong is then allowed to cool to room temperature before being incorporated into the final dough. Note that even though the hydration of a tangzhong dough using the above proportions is about 160%, the flour absorbs a large amount of the liquid — far more, in fact, than it would absorb in a standard, non-scalded dough.
Tangzhong is less a chemical than a physical process. Heating the dough-water slurry pre-cooks the starches in the flour, transforming them into a wet gel. It also hardens the proteins, making them incapable of forming the gluten that gives bread both its structure and chewiness. With increased moisture and diminished gluten-forming capacity, doughs made with tangzhong bake into the tender, close-crumbed, almost cake-like loaves of Hokkaido Milk Bread that line the bakery shelves of the Asian markets that have proliferated throughout Southern California (where I live) and elsewhere.
That said, scalding is a highly flexible technique that I think more bakers ought to explore and incorporate into their breads. The combination of milled grain and hot water enhances the ability to control the fermentation behavior of my doughs and widens the range of flavors and textures I can coax out of my finished loaves.