To have a full appreciation of grains, it is vital that you begin to appreciate their value to society. We use grains to make food, drinks, fuel and much more. The value in grain is in its stored energy, in the form of starches. Starches are an excellent energy storage molecule, taking sugars produced via photosynthesis and connecting them to form a more stable and storable form of energy.
Sugars are carbohydrates, meaning that they are made of carbon, hydrogen and oxygen. In most situations, sugars exist as ring shaped molecules. Long chain polysaccharides (starches, xylans, etc.) are formed when sugars join together in a reaction called dehydration synthesis, as one sugar loses a hydrogen atom, and another loses a hydrogen and oxygen bonded group, which together combine to form water. This usually occurs in a multi-step process in plants, combining many single or two sugar molecules to form a long chain polysaccharide.
Starches specifically refer to polysaccharides made of the monosaccharide glucose. Starches usually have tens of thousands of individual glucose molecules in them. There are many different starches, found in different plants with different lengths, degrees of branching and other characteristics.
Two types of starches are Amylose and Amylopectin, with Amylose being a relatively straight chain linkage of glucose units, and amylopectin being a straight chain with side chains coming off of it. Different plants produce amylopectin and amylose in different ratios, leading to different properties of their grains.
The difference between sticky rice and basmati rice is due primarily due to the types of starches that the two rices produce, with sticky rice having a higher ratio of amylopectin to amylose and basmati rice having a lower ratio. The reason for the difference between the rices (pictured below) is that the high degree of branching in the sticky rice allows for molecules to more easily get stuck together, creating a single mass. In Basmati rice, with less branching, the grains are firmer and stick to each other less, even when significantly overcooked.
Besides the difference in physical qualities, amylose and amylopectin have different chemical properties as well. Many enzymes that break down starches into smaller units of a few glucose molecules, which is necessary to use the energy stored in the starch, only act on the end of a chain, with some enzymes breaking starches into large units of tens to hundreds of glucoses, and others cutting off two glucoses at a time. In a starch with more branching, there are more ends that can be clipped by these enzymes, so the energy in the starches can be accessed more rapidly, whereas an amylose molecule only has two sites to cut the chain. In animals, a closely related molecule called glycogen is produced and stored in the liver, muscle cells and around the body. It serves as a fast-acting energy storage. Glycogen is a highly branched, starch like molecule with many sites for the body to break it down into simple sugars, providing immediate energy.
To access starches, cell walls made of fibrous material must be broken, gelatinizing the starch and allowing for it to be accessible to be broken down by enzymes. The strength of these walls varies based on the type of grain; hence mashing must be done at different temperatures for the different types of grain in a mash. In malted barley for instance, the cell walls have been partially broken by the malting process, so they can be gelatinized at low temperatures. Corn on the other hand has a very high gelatinization temperature, necessitating bringing corn mashes up to 200 F.
In addition to gelatinization, the different types of starches in a grain lead to different procedures for mashing. Corn is a difficult grain to mash, as not only is it’s gelatinization temperature high, but corn’s amylose is very long chained, so after gelatinizing at 200 F is complete, the corn starches are accessible, but as the temperature of the mash decreases, the amylose coils can get meshed together, making it difficult for enzymes to work on breaking them down. Therefore, the starches must be broken down at temperature for efficient mashing. It is for this reason that historically, distillers would add malted barley during the heating of the corn, and slowly gelatinize corn at lower temperatures, in hopes of maintaining enzymatic power of the barley while keeping the amylose untangled. Today, many distillers use high temperature resistant enzymes in their mashes to break down the corn amylose into smaller polysaccharides.
As always, feel free to comment with any questions, comments or concerns!
Leave a ReplyCancel reply