Sake is Biotechnology

Sake is an alcoholic beverage of Japanese origin that is made from fermented rice. It may also be spelled saké. In the Japanese language, the word sake refers to any alcoholic beverage, while the beverage called sake in English is termed nihonshu (日本酒, "Japanese liquor"). Sake is sometimes referred to in English-speaking countries as rice wine. However, unlike wine, in which alcohol is produced by fermenting sugar that is naturally present in grapes and other fruits, sake is produced by means of a brewing process more like that of beer. To make beer or sake, the sugar needed to produce alcohol must first be converted from starch.
The brewing process for sake differs from the process for beer, in that for beer, the conversion from starch to sugar and from sugar to alcohol occurs in two discrete steps. But when sake is brewed, these conversions occur simultaneously. Furthermore, the alcohol content differs between sake, wine, and beer. Wine generally contains 9%–16% ABV, while most beer contains 3%–9%, and undiluted sake contains 18%–20% (although this is often lowered to about 15% by diluting with water prior to bottling).
Production
First step, the rice used for brewing sake is called shuzō kōtekimai (sake rice). The grain is larger, stronger, and contains less protein and lipid than the ordinary rice eaten by the Japanese. The rice has a starch component called shinpaku in the center of the grains. Since sake made from rice containing only starch has a superior taste, the rice is polished to remove the bran. If a grain is small or weak, it will break in the process of polishing. This rice is used only for making sake, because it is unpalatable for eating. There are at least 80 types of sake rice in Japan. Among these, Yamadanishiki, Gohyakumangoku, Miyamanishiki and Omachi rice are very popular.
Second step, water is one of the important ingredients for making sake. It is involved in almost every major process of sake brewing from washing the rice to dilution of the final product before bottling. Mineral content can play a large role in the final product. Iron will bond with an amino acid produced by the koji to produce off flavors and a yellowish color. Manganese, when exposed to ultraviolet light, will also contribute to discoloration. Conversely potassium, magnesium, and phosphoric acid serve as nutrients for yeast during fermentation and are considered desirable. Yeast will use those nutrients to work faster and multiply resulting in more sugar being converted into alcohol. And so hard water, with a higher nutrient content for yeast, is known for producing a drier-style sake, while soft water will typically yield sweeter sake. The first region known for having great water was the Nada-Gogō in Hyogo Prefecture. A particular water source called "Miyamizu" was found to produce high quality sake and attracted many producers to the region. To this day Hyogo has the most sake brewers of any prefecture. Typically breweries source their water from wells, though lakes and rivers can be used as well. Also breweries may use tap water and filter and adjust components as they see fit.

Brewing
Sake is produced by the multiple parallel fermentation of rice. The rice is first polished to remove the protein and oils from the exterior of the rice grains, leaving behind starch. Thorough milling leads to fewer congeners and generally a more desirable product. Newly polished rice is allowed to "rest" until it has absorbed enough moisture from the air so that it will not crack when immersed in water. After this resting period, the rice is washed clean of the rice powder produced during milling and then steeped in water. The length of time depends on the degree to which the rice was polished, ranging from several hours or even overnight for an ordinary milling to just minutes for highly polished rice. After soaking, the rice is steamed on a conveyor belt. The degree of cooking must be carefully controlled; overcooked rice will ferment too quickly for flavors to develop well and undercooked rice will only ferment on the outside. The steamed rice is then cooled and divided into portions for different uses. The microorganism Aspergillus oryzae (a mold) is sprinkled onto the steamed rice and allowed to ferment for 5–7 days (Uno et al., 2009). After this initial fermentation period, water and the yeast culture Saccharomyces cerevisiae are added to the koji (rice and mold mixture) and allowed to incubate at 4 degree Celsius for about 7 days. Over the next four days, pre-incubated mixture of steamed rice (90 kg), fermentated rice (90 kg) and water (440L) are added to the fermented mixture in three series. This staggered approach allows time for the yeast to keep up with the increased volume. The mixture is now known as the main mash, or moromi (醪, also written 諸味).
The main mash then ferments, at approximately 15-20 degree Celsius for 2–3 weeks. With high-grade sake, fermentation is deliberately slowed by lowering the temperature to 10 °C (50 °F) or less. Unlike malt for beer, rice for sake does not contain the amylase necessary for converting starch to sugar and so it must undergo a process of multiple fermentation. The addition of A. oryzae provides the necessary amylases, glucoamylases, and proteases to hydrolyze the nutrients of the rice to support the growth of the yeast(S.cerevisiae). In sake production these two processes take place at the same time rather than in separate steps, so sake is said to be made by multiple parallel fermentation. After fermentation, sake is extracted from the solid mixtures through a filtration process. For some types of sake, a small amount of distilled alcohol, called brewer's alcohol (醸造アルコール), is added before pressing in order to extract flavors and aromas that would otherwise remain behind in the solids. In cheap sake, a large amount of brewer’s alcohol might be added to increase the volume of sake produced. Next, the remaining lees (a fine sediment) are removed, and the sake is carbon filtered and pasteurized. The sake is allowed to rest and mature and then usually diluted with water to lower the alcohol content from around 20% to 15% or so, before finally being bottled.
Maturing
The process during which the sake grows into a quality product during storage is called maturing. Mature sake has reached its ideal point of growth. New sake is not liked because of its rough taste, whereas mature sake is mild, smooth and rich. However, if it is too mature, it also develops a rough taste. Nine to twelve months are required for sake to mature. Aging is caused by physical and chemical factors such as oxygen supply, the broad application of external heat, nitrogen oxides, aldehydes and amino acids, among other unknown factors. It is said that Saussureae radix from the Japan cedar material of a barrel containing maturing sake comes to be valued, so the barrel is considered indispensable. Special-designation sake, there are two basic types of sake: Futsū-shu (普通酒?, Ordinary sake) and Tokutei meishō-shu (特定名称酒?, special-designation sake). Futsū-shu is the equivalent of table wine and accounts for the majority of sake produced. Tokutei meishō-shu refers to premium sakes distinguished by the degree to which the rice has been polished and the added percentage of brewer's alcohol or the absence of such additives. There are eight varieties of special-designation sake.
Three ways to make the starter mash
    Kimoto (生酛) is the traditional orthodox method for preparing the starter mash, which includes the laborious process of grinding it into a paste. This method was the standard for 300 years, but it is rare today.
    Yamahai (山廃) is a simplified version of the kimoto method, introduced in the early 1900s. Yamahai skips the step of making a paste out of the starter mash. That step of the kimoto method is known as yama-oroshi, and the full name for yamahai is “yama-oroshi haishi” (山卸廃止), meaning “discontinuation of yama-oroshi.” While the yamahai method was originally developed to speed production time, it is slower than the modern method and is now used only in specialty brews for the earthy flavors it produces.
    Sokujō (速醸), "quick fermentation", is the modern method of preparing the starter mash. Lactic acid, produced naturally in the two slower traditional methods, is added to the starter to inhibit unwanted bacteria. Sokujō sake tends to have a lighter flavor than kimoto or yamahai.
Different handling after fermentation
    Namazake (生酒) is sake that has not been pasteurized. It requires refrigerated storage and has a shorter shelf-life than pasteurized sake.
    Genshu (原酒) is undiluted sake. Most sake is diluted with water after brewing to lower the alcohol content from 18-20% down to 14-16%, but genshu is not.
    Muroka (無濾過) means unfiltered. It refers to sake that has not been carbon filtered, but which has been pressed and separated from the lees, and thus is clear, not cloudy. Carbon filtration can remove desirable flavors and odors as well as bad ones, thus muroka sake has stronger flavors than filtered varieties.
    Nigorizake (濁り酒) is cloudy sake. The sake is passed through a loose mesh to separate it from the mash. It is not filtered thereafter and there is much rice sediment in the bottle. Before serving, the bottle is shaken to mix the sediment and turn the sake white or cloudy.
    Seishu (清酒), "clear/clean sake", is the Japanese legal definition of sake and refers to sake in which the solids have been strained out, leaving clear liquid. Thus nigorizake and doburoku (see below) are not seishu and therefore are not actually sake under Japanese law. However, nigorizake can receive the seishu status by being strained clear and having the lees put back in afterward.
    Koshu (古酒) is "aged sake". Most sake does not age well, but this specially made type can age for decades, turning yellow and acquiring a honeyed flavor.
    Taruzake (樽酒) is sake aged in wooden barrels or bottled in wooden casks. The wood used is Cryptomeria (杉, sugi), which is also inaccurately known as Japanese cedar. Sake casks are often tapped ceremonially for the opening of buildings, businesses, parties, etc. Because the wood imparts a strong flavor, premium sake is rarely used for this type.
    Shiboritate (搾立て), "freshly pressed", refers to sake that has been shipped without the traditional six-month aging/maturation period. The result is usually a more acidic, "greener" sake.
    Fukurozuri (袋吊り) is a method of separating sake from the lees without external pressure by hanging the mash in bags and allowing the liquid to drip out under its own weight. Sake produced this way is sometimes called shizukazake (雫酒), meaning "drip sake".
    Tobingakoi (斗瓶囲い) is sake pressed into 18-liter bottles ("tobin") with the brewer selecting the best sake of the batch for shipping.
    Amazake (甘酒) is a traditional sweet, low-alcoholic Japanese drink made from fermented rice.
    Doburoku (濁酒) is the classic home-brew style of sake (although home brewing is illegal in Japan). It is created by simply adding kōji mold to steamed rice and water and letting the mixture ferment. The resulting sake is somewhat like a chunkier version of nigorizake.
    Jizake (地酒) is locally brewed sake, the equivalent of microbrewing beer.
    Kuroshu (黒酒) is sake made from unpolished rice (i.e., brown rice), and is more like Chinese rice wine.
    Teiseihaku-shu (低精白酒) is sake with a deliberately high rice-polishing ratio. It is generally held that the lower the rice polishing ratio (the percent weight after polishing), the better the potential of the sake. However, beginning around 2005, teiseihaku-shu has been produced as a specialty sake made with high rice-polishing ratios, usually around 80%, to produce sake with the characteristic flavor of rice itself.