1. Introduction

Wheat is one of the three most important cereals worldwide in terms of production and consumption. According to FAOSTAT [1], the estimated annual production in 2014 was 728 million tons, which provided daily 178 g per capita to the average human being. Wheat is considered among the oldest crops and is grown in more than 120 countries around the globe [2] and is the

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main cereal in the human diet worldwide due to its agronomic adaptability, storability, nutritional value and diversity of products produced from it [3]. Wheat is unique among grains because its protein mixed with water and mechanical work yields a viscoelastic dough or batter capable of trapping gases produced by yeast or baking powders producing and array of leavened products such as breads, cakes and cookies.

Cereals grains are biological materials that differ in features due to many factors such as cultivar or genotype, soil fertility, growing conditions and agronomic practices [4]. The classification and grading play an important and critical role in the market because assures quality control guidelines. Furthermore, the standardization of grain quality allows a better marketing and grain processing to produce different products. Selected grain types for specific uses relate to their physical properties because they affect chemical composition, functionality and optimum industrial end use. The standardization of grain quality allows process a grain's lot with similar grade or quality [5].

Different methods for the classification of wheat grains are based on growth habit, end use and physical characteristics. The use of these methods can be referred to as technological classification [6]. Wheat-based products require different classes of the grain for their processing. Industrial quality is characterized by physical, chemical and rheological analysis related with roller milled refined flour, used especially in the manufacture of yeast-leavened breads (hard wheat) or chemically leavened cookies and cakes (soft wheat) or to produce semolina to elaborate long and short pasta products (durum wheat).

Physical evaluation of the wheat kernels offers a first and interesting quality control for selection as raw materials because the kernel physical features are related with design of equipment, handling, aeration and storage as well as to end use. Increasingly, analyses are implemented to assess the inherent characteristics of the grain to better know their attributes. The study of wheat kernel characteristics is necessary because new cultivars (with new and different properties) are constantly being bred and produced [7].

This chapter reviews the principal physical properties of wheat kernels in three sections. The first covers aspects related to appearance and damage, the second addresses shape and size features and the third grain volume, weight and density.
