Is There a Difference Between Rolled and Flaked Grains?

Thanks for the great question, Tony! An interesting topic to dive into for sure because there are some real differences among adjunct grains that are invisible to the eye. For starters, the terms “flaked” and “rolled” are indeed used interchangeably. It seems that some writers have learned that repetitive words make for odd-looking sentences and use the term “rolling” as the process of producing “flaked” grains. Here is an example from the interwebs: “To create rolled oats, whole grain groats are first steamed, then rolled flat into flakes.” And here is a headline from a website about using a handheld grain flaker titled “Make Rolled Oats & Flaked Grains.” In this case, one piece of equipment called a grain flaker (attaches to a KitchenAid® stand mixer) functions in a single manner to produce “rolled oats” and “flaked grains” . . . or is that “flaked oats” and “rolled grains”? Suffice to say, the flat things that make for a healthy bowl of oatmeal are known as rolled and/or flaked oats.

Semantics aside, there are very real differences in how grains are treated prior to being squished into flat bits. For the sake of clarity, I will use the terms “rolling” and “rolled” for the remainder of this answer to describe the rolling process and the resultant rolled grain. There are essentially four different preparation methods before the pre-rolled grain meets the roller. The first is to simply clean or screen grains to remove dust, rocks, etc. before rolling. This method works well enough, but the rolled grains can literally look a bit rough around the edges and are not terribly shelf stable because rolling exposes the inside of the grain to oxygen. This is an important issue with oats because oats contain lipids (fats) that turn rancid over time. Other grains, like barley, wheat, and rye, contain much less lipids and are not known for being prone to rancidity. Rolled, unprocessed grains are most common among home rollers of grain.

When raw grains are wetted prior to rolling, the resultant rolled grain is more uniform in appearance and is easier to produce. The most common way to moisten raw grains in a commercial production plant is with steam. Steaming the raw grain has two key advantages from a brewing perspective: 1) Steaming heats and hydrates starch granules and 2) Steam heating denatures enzymes. Immediately following the steam step, the grains are rolled and then cooled. These steam-rolled grains usually have a longer shelf life compared to raw-rolled grains because of enzyme denaturation and the grain starches are also gelatinized in the process.

As a quick aside, none of these methods were developed to help brewers with brewing or to make the preparation of that morning bowl of oatmeal faster to get onto the table. The science of grain rolling and the nuanced differences in the rolled products all came out of research conducted to optimize feed utilization for beef production. For a really interesting review of the history of this topic, search “History of Feed Processing, John K. Matsushima” and check out his review from the 2006 Cattle Grain Processing Symposium.

In the pursuit of more complete gelatinization, scientists continued to pursue refinements to steaming and rolling. This is why there are so many different thicknesses of rolled grains. In about 1970, the process of micronization was developed. So-called micronized grains are heated using a dry, indirect heating source to cause the starch granules to swell and burst. Popcorn is a common example of this basic process, except with micronization infrared energy is used as the heat source.

The term micronization is not a common term outside of the animal feed world and the same process is more commonly known as torrefication. The products of the process are known as “micronized,” “torrefied,” and “puffed.” Name aside, a real difference between micronization and steaming is more complete gelatinization of the starch. This distinction is key in animal nutrition, especially with horses (non-ruminant herbivores), because it significantly affects nutrient uptake and feed utilization, a.k.a. feed cost.

Micronized/torrefied grains can be rolled just like steam-cooked grains. Examples of these products include torrefied wheat (not rolled) and flaked torrefied wheat, oats, rye, barley, rice, and maize (corn).

Toasting is yet another pre-rolling preparation technique. While toasting uses the same sort of process of micronization, the term “toasted” is not used to describe how animal feed stuffs are made and published data quantifying differences among other rolled grains is not readily available. Most toasted and rolled adjuncts are indeed very similar to “flaked torrefied [micronized] grains” but there are whole toasted grain products that do not have a puffed appearance; these toasted grains are more akin to lightly roasted grains. Up until now, things have been fairly clear. Unfortunately, “toasted” does not have a single definition universally used by all processors. For any commercial brewer reading this, the best way to understand what you are dealing with is to request a Hazard Analysis Critical Control Points (HACCP) process flow diagram from your supplier to understand the method(s) being used in the production of your raw materials.

And finally, let’s touch on milling. The advantage of milling rolled grains is increased extract yield. Digging around in spent grains after the kettle is full is a really great way to see how things went in the mash. Whole malt kernels, easier to spot in spent grains than in milled grist, obviously did not yield their extract and represent loss. Likewise, large bits of rolled grains have largely gone unchanged by the mash. A great visualization is to squeeze one of these rolled bits onto a spoon and drop in a bit of iodine. A jet-black result confirms the presence of starch and indicates that goodies are present in the spent grains. Many brewers don’t want to mill rolled grains for fear of sticking the mash. That’s a legitimate concern, but so is adding an ingredient that ends up being discarded after the process.
Hopefully this clears things up a bit on the topic of steamed, puffed, micronized, toasted, and torrefied, rolled or flaked, grain flakes.

What is Gelatinization?

Starch granules are microscopic spheres containing crystalline, tightly packed starch molecules. Nature’s form of a packet of energy stuffed into a ball. Within these granules is a mixture of amylose (straight-chained) and amylopectin (branched) starch molecules. The ratio of these starches varies between and within cereals bred and grown for starch. For example, “normal” maize/corn, contains about 75% amylopectin and 25% amylose, waxy maize is about 99% amylopectin, and high amylose maize starch is about 75% amylose and 25% amylopectin. When starch granules are viewed under a polarized light microscope, they have a distinctive appearance often called a Maltese Cross due to birefringence of polarized light (think Pink Floyd’s Dark Side of the Moon album cover).

When starch granules are hydrated and heated, they swell and eventually burst. From a practical sense, this can be felt when stirring a starch solution over a heat source. Upon gelatinization, the solution thickens, becomes more voluminous, before the viscosity drops when the granules burst. And if you happen to be visualizing this using a polarized light microscope, birefringence is lost and the Maltese Cross disappears. Very cool stuff. This is important to brewers because hydrolytic enzymes from malt can now break down these large molecules into fermentable sugars. It’s as simple as saying no gelatinization, no beer!

One crazy thing about gelatinized starch is that it stales by a process known as retrogradation. When starch retrogrades, it re-crystallizes. This is the primary path of how bread stales. Speaking of stale and moldy bread, those problems seem to have dropped off the radar over the last fifteen years or so. How is that? Well, exogenous alpha and beta amylases are now commonly used by commercial bakeries to alter the starch structure before baking, thereby preventing starch retrogradation. And organic acids, like acetic (vinegar), propionic, isovaleric, and butyric (all naturally found in cheeses) do a great job of inhibiting mold growth. This one-two combo has all but eliminated fuzzy loaves of hard bread.

Although most rolled grains tend to look similar, don’t assume they are all the same. The pre-rolling method has a significant effect on gelatinization rate. This means that some rolled grains can be chucked into an infusion mash where they will dissolve and easily release gelatinized starch into the mash. Other rolled grains are gelatinized to varying degrees and either require cooking or greatly benefit from cooking prior to use. A process known as cereal mashing is one way to gelatinize grains. But that is a whole other topic to cover another day.

Response by Ashton Lewis.