Future-Proofing Healthy Flours

Grain milling is the oldest food manufacturing process in the world. Cereal grains are mostly milled to produce flour, which becomes the main ingredient in bakery, pasta, and various processed food products. The wheat milling process involves mainly two primary operations: grinding and separation. Grinding of various grains is carried out primarily using a roller mill or a stone mill using both shearing and compression forces. Separation is typically handled by a sifter according to particle size differences. Of the two, the traditional process of stone milling holds significant advantages over modern milling methods, including the higher nutritional and functional value of the flour produced and versatility of application in small- to large-sized operations.

How Stone Milling Works

Although an ancient process, stone milling is still used throughout the world today. The process is versatile and can be utilized to grind different grains. Stone mills are primarily used in whole grain flour production. The American Association of Cereal Chemists has suggested that whole grain flours should consist of all the principal anatomical components of a grain–endosperm, germ, and bran–in the same relative proportion (AACC 2000, Frolich and Aman 2010). Nutrients are distributed unevenly in the grain; bran is rich in fiber and minerals, germ stores fat along with protein, and endosperm is mainly composed of starch and proteins.

During whole grain stone milling, all the components of the grain are ground to make flour that retains nutritional components intact, as compared to the roller milling process for production of refined flours in which nutrients are usually removed. Refined flours mainly consist of the starchy endosperm of the grain, since the germ and bran are removed during the roller milling process.

The stone milling unit consists of a grain hopper to hold the cleaned grain, the grinding stones, and a sifter. The grains are fed to the grinding stones in a controlled manner by volumetric auger. The grain feeding rate may vary for different grains depending on their physical properties as well as the desired flour granulation and extraction. The stone mill’s pair of horizontal circular stones, often made of granite, are placed one on top of the other. The upper stone, known as the “runner,” rotates, and the lower stone, called the “bedstone,” is fixed to the body of the mill. The conical center part of the upper stone provides for an easy feeding of the grains in the grinding zone. The runner stone is driven from below by the drive motor. The grinding stone surfaces feature a series of furrows, such as main furrows, side furrows, and grinding furrows. The grinding takes place between the two stones as grains move from center to periphery, which converts the grains into flour. The degree of fineness of the flour is controlled by adjusting the gap between two stones.

The final operation of the unit is the sifter. A sifter consists of sieves that can be selected as per the operation’s requirement of the level of flour granulation. The flour is sifted through various sieves to produce fine flour. Particles that stay over the sieve are collected at the end and mainly contain relatively bigger bran particles. Since the stone mill is typically used to produce whole grain flour, sifting is not required, although it can be used for production of flour with different extraction (for small portion of bran removal), depending on the requirement. The advantages of stone mills are:

• The unit is small and compact.
• The process is versatile and offers the capability of grinding different grains.
• It can be used for grinding flour for domestic use or small bakeries as well as scaled up for industrial use.
• The process results in flour with higher nutritional and functional value.
• The process allows adjustment of the extraction rate of flour.
• By adjusting the stone gap and the sieve size, the flour granulation can be customized and changed according to specifications.

Nutritional Benefits

Consumers are choosing healthier and more flavorful foods, which has brought a renewed popularity of the stone milling process in recent years. As a result, many bakers, food processors, and developers are shifting toward using whole grain flours due to their health benefits. Nutrient-rich stone ground whole grain flours can be considered a healthier choice for development of products such as bread, baked goods, pasta, and cookies. Whole grain flours are nutritionally dense, boasting a diverse array of health-promoting compounds such as vitamins, minerals, dietary fiber, and phytochemicals. They are rich sources of complex carbohydrates, providing sustained energy release and satiety. Additionally, whole grain seeds are replete with essential vitamins, including B vitamins (thiamine, riboflavin, niacin, and folate) and vitamin E, all of which play pivotal roles in energy metabolism, nerve function, and antioxidant defense mechanisms. Furthermore, whole grain flours serve as abundant sources of minerals such as magnesium, zinc, iron, and selenium, contributing to various physiological processes, including bone health, immune function, and antioxidant activity (Dietary Guidelines for Americans 2015-2020).

In addition to their macronutrient and micronutrient content, whole grain flours harbor an array of phytochemicals and bioactive compounds with potent antioxidant and anti-inflammatory properties (Călinoiu and Vodnar 2018). The consumption of whole grains can help improve blood metabolic profiles. They provide protective effects with richer insoluble or viscous fibers, assisting in lowering levels of blood sugar, serum total cholesterol, and low-density lipoprotein cholesterol (Davis 2014). Also, consumption of whole grains in the medium- to long-term could result in a decrease in fasting glucose levels compared to equivalent refined foods. Achieving optimal intervention dosage and accurately selecting target populations could be crucial factors for whole grain intake to effectively regulate glycemic control (Li et al 2022).

Whole grain flour consumption has been associated with numerous health benefits, including reduced risk of cardiovascular disease, type 2 diabetes, obesity, and certain cancers (Benisi-Kohansal et al. 2016). Polyphenols, phytosterols, tocopherols, carotenoids, flavonoids, phenolic acids, and lignans are prominent constituents of whole grain seeds, exerting protective effects against chronic diseases by scavenging free radicals and modulating inflammatory pathways. They contribute to antioxidative and cardioprotective properties, highlighting their potential in mitigating cardiovascular risk factors (Călinoiu and Vodnar 2018). Moreover, the synergistic interactions among phytochemicals and bioactive compounds present in whole grain seeds confer additional health benefits, including anti- inflammatory and anti-cancer effects (Liu 2007).

There are other benefits of stone ground whole flours apart from nutrition. The presence of germ gives stone ground whole grain flour a characteristic nutty flavor and aroma, highly sought sensory attributes for product development. Due to the use of shear and compression forces in the stone mills, heat generated during milling causes the development of damaged starch and aromatic components in flour. The smaller particles of damaged starch hydrates easily during dough preparation and contributes to gas production during fermentation and proofing, which influences the overall product quality (Arya et al. 2015). A reasonable amount of damaged starch enhances water absorption of the dough resulting in softer breads.

Future Forward

Stone milling has come a long way from the small, manual systems to modern-day automated units to produce whole grain flours. With the nutrients intact in the flour, they can be utilized as healthy alternatives. Embracing stone milling helps preserve an age-old technology and keeps cultural heritage alive for future generations. Northern Crops Institute’s (NCI) initiative looking into the feasibility of using stone milling to produce whole grain and other flours suggests that this processing method can be successfully used by smaller enterprises such as bakeries as well as scaled up to accommodate the output needs of larger operations. NCI reported its outcomes in a handbook, which demonstrates the details of a stone mill and the milling parameters of various grains with experimental results, and in courses that facilitate hands-on training and education about stone milling operations, flour quality, and baking (NCI 2023, NCI 2024).ft