Stone milling or cylinder milling, what are the differences and what impact on the quality of flours, as well as the resulting products? The scientific review of the University of Florence, published in Trends in Food Science & Technology. ‘Stone milling versus roller milling: A systematic review of the effects on wheat flour quality, dough rheology, and bread characteristics‘.
‘Stone-ground. Historical courses and recourses
Stone grinding of grain is illustrated in some ancient Egyptian stelae, dated around 2600 BC (Walker & Eustace, 2016). And it continued until 1900 AD through stone mills, which were then gradually replaced with cylinder mills.
Certain agronomic and food processing practices have since come back into vogue as the new millennium dawned. With the goal of rediscovering the symbiosis between nature and food, respecting ecosystems and biodiversity. Tradition, agroecology and solidarity, health. Not in words but in deeds, with initiatives whose results have been the subject of numerous scientific studies.
The rediscovery of ancient grains and the development of sustainable practices has even made it possible to achieve a negative, i.e., pro-environmental,carbon and ecologicalfootprint in the pasta production chain.
‘Stone-ground’ is a claim that is beginning to emerge, as is already the use of ancient grains, on a growing number of labels for flour, pasta, and baked goods. Thanks to the recovery of old mills and new investments in state-of-the-art stone mills. Investments that seem naïve to believe are motivated by marketing needs alone, given their impact on operating costs and production logic itself.
Milling techniques and properties of flours
The choice of milling method is a key aspect of the production process, as the physicochemical and functional properties of wheat flour and derived products, especially pasta and bread, are significantly affected (Doblado-Maldonado et al., 2012; Li, Dhital and Hasjim, 2014).
The first and foremost factor influencing milling technique is obviously the type of wheat used. From the hard grains, semolina is obtained and is used mainly for making pasta; from the soft grains, flour is obtained and used to make bread and baked goods.
Numerous studies have shown how the milling system used–for wheat, rice, sorghum, barley, and rye–affects color, particle size, surface appearance, bulk density, and starch quality. In addition to the structure and functional properties of the flour, and related physicochemical properties (Albergamo et al., 2018; Cubadda et al., 2009; Ficco et al., 2016; Kihlberg, Johansson, Kohler, & Risvik, 2004; Liu et al., 2018; Palpacelli et al., 2007; Yu et al., 2018).
Dough rheology and breadmaking
The rheology of the dough (viscosity and elasticity) and the baking process obviously depend on a number of factors. Not only the milling but also the type of flour, water dosage, temperature and duration of mixing, type of kneading machine, use of soil conditioners, operator discretion, and type of yeast used are just some of the factors that influence the final result.
The milling technique nonetheless-both in the face of the variety of factors mentioned above-it turns out to be a determinant on flour quality, dough rheology, and bread characteristics (Albergamo et al., 2018; Cappelli, Guerrini, Parenti, Palladino, & Cini, 2020; Cubadda et al., 2009; Ficco et al., 2016; Kihlberg et al., 2004; Liu et al., 2018; Palpacelli et al., 2007; Yu et al., 2018).
Nutraceuticals and nutritional profiles
The main advantage of stone milling, in whole-wheat flour, is the preservation of endosperm, bran and germ in their natural proportions. In a symbiosis that is actually perceived as ‘natural’ by the consumer. And it expresses, not surprisingly, a better endowment of all the most important nutritional/nutraceutical compounds contained in the germ and outer bran layer (Di Silvestro et al., 2014).
Protein and crude fat contents are significantly higher in stone-milled flours compared with those from cylinder milling:
– protein, 11.4% vs. 7.3%,
– fat, 2.1% vs. 0.9%.
Conversely, the total starch content is higher in cylinder milling flour (77% vs. 70%. Liu et al., 2018).
Micronutrients
The mineral content-in stone-milled semolina and flour-is unaltered in trace elements (manganese, iron, copper, zinc, and selenium). And minimally reduced in macroelements (sodium, magnesium, potassium, calcium and phosphorus). To the point of considering, in this respect, that flour and semolina obtained from stone mills have a high nutritional value (Albergamo et al., 2018).
In contrast, the decrease in minerals in cylinder-milled flours and semolina appears marked (Cubadda et al., 2009). With significant reductions on selenium (77-85%), calcium (54-60%), copper (49-53%), potassium and phosphorus (42-47%), iron (36-38%), and magnesium and zinc (32-36%).
Sensory qualities
In turn, the sensory qualities of whole-wheat flour products are found to be significantly influenced by milling technique (Kihlberg et al., 2004). Whole-wheat flours obtained by stone milling show lower water absorption than cylinder milled samples (while the opposite trend was observed for wheat milling and subsequent blasting).
Whole-wheat bread made with flour from stone milling is characterized by a crisp crust, a more pronounced flavor profile, and greater sensitivity to crumbling. The starch that formed the bread crust, at the same time, appears to have suffered less damage. While the crispness can be attributed to the heat produced during flour milling.
Cylinder grinding. Effects on flour, dough and bread
Wheat flour from cylinder milling is found to have a higher amount of damaged starch than the product derived from stone milling (Kihlberg et al., 2004).
Wheat germ is found to be subject to more pronounced oxidation and rancidity (Boukid, Folloni, Ranieri and Vittadini, 2018). As for the rheological properties of the dough, the bread has a higher consistency, higher water absorption, superior stability (Kihlberg et al., 2004).
Finally, particle sizes in cylinder milling flours are less homogeneous. With a wider particle size distribution, particularly in the ranges > 1120 μ and ≤250 μ (Kihlberg et al., 2004; Liu et al., 2018).
Traditional and modern stone mills
The traditional watermill, described by Aristotle in 400 B.C., uses the current of water powering a gear mechanism (Walker & Eustace, 2016). Flours obtained from traditional mills (at temperatures of about 30°C) differ from those from modern stone mills (at about 60°C) in several respects:
– Higher starch content (68.1 percent vs. 61.6 percent),
– Lower amount of insoluble fiber,
– plus polyphenols and flavonoids (Di Silvestro et al. 2014).
Cylinder mills, the good points
The scientific literature confirms how the evolution of grinding techniques has enabled cylinder mills to achieve greater efficiency and especially flexibility than stone mills. A very important factor because it allows the mill to be calibrated differently in relation to the type of grain to be ground, an operation that is impossible for stone mills (Doblado-Maldonado et al., 2012).
The shelf-life of the resulting flour is superior due to the separation of the germ from the rest of the caryopsis. In fact, the germ contains most of the lipids in the grain, and its removal causes inhibition of lipase activity. As a result, the shelf life of flours is extended, without affecting their functional properties (Doblado-Maldonado et al., 2012).
Interim conclusions
Mill you go, flour you find. Both types of milling have advantages and disadvantages, depending on the different objectives:
– stone milling is favored to make products with more pronounced nutritional and nutraceutical qualities, also in a logic of short supply chain that considers the links between traditions and territories,
– cylinder milling, on the other hand, makes it possible to meet demands for high quantities of flour and semolina suitable especially for industrial processing. To combine the different needs, several modern mills are equipping themselves with both systems.
It is worth noting the coexistence of other factors that determine the quality characteristics of flour products. The soils cultivated and the wheat varieties chosen, even in mixtures, processing techniques, grain moisture, etc.
Paolo Caruso and Dario Dongo
Bibliography
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Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
Agronomist, collaborates with the Department of Agriculture, Food and Environment of the University of Catania, Agronomy and Herbaceous Crops section. Researcher on ancient Sicilian grains.
