Distillation methods and operating techniques
Batch distillation: double distillation
When malt whiskey is double distilled in a pot still, the most common method is to put it simply: the fermented juice is distilled in a pot still to obtain a low-alcohol liquor, and is mixed with the double-distilled head and tail. , and then distill it in a spirit still to obtain new wine.
wine distillation
Although the temperature of the fermented wine juice exceeds 30°C, if it is placed directly into the distiller for heating, it is easy to cause a large temperature gap between the distillate and the copper wall due to the better thermal conductivity of the copper wall, resulting in residual protein and very little in the wine. The sugar is charred due to thermal cracking when it contacts the copper wall, which is called the Maillard reaction. In order to avoid this phenomenon, it must be preheated before loading. Generally, a plate heat exchanger is used to heat a batch of distilled high-temperature wine residues to about 60°C, and then temporarily stored in the loading tank, and then pumped Send it to the still.
When starting to load, you must first close the unloading valve and open the ventilation valve, and then fill to the bottom of the cleaning inlet cover. Then close the loading valve and the cleaning inlet cover. Check whether the safety valve on the swan neck is operating normally before starting. Heating, if foam occurs, you can use the observation window on the swan neck to pay attention to the growth and decline of the foam. If necessary, add defoaming agent (anti-foam) or lower the heating temperature to prevent the foam from rushing out of the Lynn arm and causing abnormal distillation ( foul distillation). The defoaming agent is a food-grade surfactant, and the amount added is small. For Brady's distiller of about 17,000 liters, only 150 ml is enough, and it is not necessarily necessary to use it. If the temperature can be lowered to lower the foam position, Then just maintain this temperature to allow the low-alcohol wine to condense and flow out stably.
The distillation of the wine juice continues until the alcohol content reaches 1%. At this time, almost all the alcohol contained in the wine juice has been distilled out. Therefore, the amount of low-alcohol wine can be simply calculated based on the alcohol content as follows: Assume that the alcohol content of the wine juice is 8 %, the average alcohol content of low-alcohol wine is 24%, then the low-alcohol wine is about one-third of the loading. When the distillation is completed, open the unloading valve to avoid negative pressure in the still. The remaining solid dregs can be separated and heat exchanged with the next batch of wine juice. The solid material still contains protein and has been used as animal feed since ancient times. However, the liquid is useless and should be discharged after environmental protection treatment. The above-mentioned time required from loading to unloading is about 5 to 8 hours, of which the time required from loading to unloading is about 0.5 to 1 hour. It is observed that the distillation time varies among distilleries due to different preheating temperatures and heating rates. .
Heating rate is an important consideration because intense heating can produce massive surging. If the wine juice is full of fine particles and is relatively turbid, if the still is filled relatively full or is long and tall, in order to allow the heat from the bottom to be conducted to the top, the input heat must be increased, and this high temperature will cause the distillation to be in contact with the bottom of the tank (direct fire) or The liquid in (indirect) contact with the steam pipe evaporates immediately, causing the steam to surge upward in waves, causing the low-alcohol wine flowing into the safe to also erupt in waves. There is no risk, but if the flow rate cannot be reached for a long time, it will be very difficult to control and the collector in the safe may be destroyed. In addition, if the indirectly heated steam pipe is blocked and the input heat is unstable, this phenomenon will also occur, even in spirit distillers. Therefore, regular cleaning of the steam pipe is very important for distillery management.
During the primary distillation and condensation, the young Wolfburn Distillery adjusts the amount of condensation water so that the water temperature in the condenser is slightly higher than 20°C to retain more malt flavor. When observing the operation, the safe lid must be opened , use your sense of smell to judge the appropriate temperature, or you can record it at a certain height of the condenser, feel the temperature with your hand, and adjust the size of the valve accordingly to control the amount of water flowing into the condenser. This ancient technique is called run hot. Distillery manager Shane Fraser used this method in his early years at the Royal Bluehorn Distillery, but it seems to have been forgotten by the industry because even whiskey master Charles Maclean is not aware of this method.
2. Spirit distillation
The loading, heating and unloading process of the spirits distiller is not much different from that of wine distillation, including the loading capacity and opening and closing of pipe valves and other precautions. However, due to the high alcohol content of the distillate, preheating is generally not required. To avoid the loss of alcohol through evaporation, some wineries still consider cost-effectiveness and still pre-heat in sealed containers to reduce the heat input required during distillation.
The spirits distiller will produce three parts: foreshots head, middle cut heart and feints tail. The head is the earliest part to be released, and the alcohol content can reach up to about 85%. And it is rich in highly volatile compounds such as ethyl methanol, etc., which is not suitable for drinking: when the alcohol content gradually decreases to less than about 75% (different from each winery), the (Demisting test) proves that the wine is relatively clear After that, you can start to collect the heart of the wine that is suitable for drinking. When the alcohol content continues to decrease and the content of heavier polymer substances such as fatty acids and fusel oil gradually increases, you can turn to the tail of the wine. At this time, the alcohol content is about 62 % (varies for each winery) and collected all the way down to 1%.
The spirits of each batch are now stored in the Intermediate Spirit Receiver (ISR), and then input into the Spirit Warehouse Receiver Vessel (SWRV). After adding water, they are diluted to the barrel alcohol content set by the distillery. After that, it can be poured into oak barrels to begin maturation. As for the head and tail of the wine, it is mixed with the next batch of low-alcohol wine before the next batch of spirits is distilled.
Not all wineries have ISR, and the new wine produced by some wineries is sent directly to SWRV and then diluted into barrels. The advantage of ISR is that if there is a problem with the distillation of a certain batch, for example, if the heart of the wine is cut at the wrong point, then only one batch of wine will be wasted, and the entire week's work will not be wasted (if the SWRV capacity can be filled with 1 production volume per week), and it is also easier for ISR to calculate the new wine output of each batch.
In the new distilled wine, different compounds have different boiling points and different flavors. The compounds contained in the wine head include low-boiling acetone, acetaldehyde, methanol, ethyl formate and highly volatile sulfides, as well as some dissolved in high-temperature alcohol. Alcoholic fatty acids, etc. not only smell bad, but are also harmful to the human body. The closer to the end of the wine, the more the flavor tends towards the flavors of leather, tobacco, ashes or cheese. The phenols and smoke present in peated whiskey are also at the end of the extraction of the heart of the wine. If you take too much of the heart of the wine, various flavors may appear. A mellow smell, such as the famous soapy smell that a certain winery talked about in the 1980s, is most likely caused by cutting too much. Therefore, we must be very careful when switching from the head of the wine to the heart of the wine, and from the heart of the wine to the tail of the wine. If the extraction range of the wine core is narrow, it will consume a lot of energy and cost, and if the range is too wide, the flavor will be mixed.
The alcohol content of the low-alcohol wine produced by the distillation of wine juice is about 24%. After being mixed with the head and tail of the previous batch, the alcohol content may be higher than 30%.
Since molecular substances such as heavy oil esters are insoluble in water but soluble in alcohol, if the alcohol content of the distillate is less than 30%, the heavy oil esters will separate and float on the top, and only a few will dissolve in the lower layer. Once the alcohol is too high, , then the content of heavy oil esters dissolved in the distillate is high. During distillation, not only may it be impossible to obtain a clear result (defogging test), but the obtained wine may also be filled with an unpleasant tail flavor.
However, even if the alcohol content of the distillate is reduced to less than 30%, the heavy oil esters floating in the upper layer may still mislead the results (defogging test) after distillation. In order to solve this problem, first, after mixing low-alcohol alcohol into the head and tail of the liquor, water must be added to dilute it to reduce the alcohol content to less than 30%, and then the heavy oil esters are removed by adsorption to prevent these substances from entering the spirit distillation. device.
(Demisting experiment) The traditional method is used, and the method has been decided to start extracting the heart of the wine. Because the alcohol content of the wine head is high, more oils and fats can be dissolved. Therefore, during operation, add water to the liquor in the safe to dilute it to 45.7%. Oils and esters that are insoluble in water will emerge and make the diluted liquid appear turbid and mist-like. This kind of experiment needs to be carried out several times, but experienced distillers can easily judge that when the diluted head is added and the wine becomes clear, it is time to switch to extracting the heart of the wine.
But even if it is traditional, there is a problem in how to add water to dilute it to 45.7% alcohol content. Regarding this question, Doug Mclvor, head of the spirits department of Berry Bros. (BBR), said that from memory, water should be added slowly. It is speculated that the distillery can, based on experience, take a certain amount after starting distillation for a period of time. Add a certain amount of water to the wine head, only for quality control testing.
Interestingly, Strathearn, currently the smallest distillery in Scotland, determines the cut-off point purely by dipping your fingers into the wine to test the wine, which is definitely the oldest method. Of course, relying on artificial methods (defogging experiments) or relying on sensory judgment will inevitably lead to different quality. Most wineries no longer use it. Instead, they use machines to record the temperature, alcohol content, etc. of the new distilled wine, or directly use computers to manage the extraction of wine. Taking careful time can minimize human errors. Some distilleries are somewhere in between, such as Glen Grant. Each distillation batch is still measured by a dedicated person for alcohol content, and then compared with computer numbers.
Generally, the time required for spirits distillation from loading to unloading is about 5 to 8 hours, which is roughly the same as primary distillation. However, each distillery varies greatly. It may take more than 12 or 13 hours, or it may only take 5 or 6 hours. Adjust the time required for other processes, including saccharification and fermentation, so that the operation of the winery can form an effective rhythm. But no matter what the shape of the still is, the heating rate - that is, the heat input per unit time, has a decisive influence. The rate is fast, and the alcohol vapor pressure generated is high, which can easily break through the multiple reflux traps and condense, and the action time on copper is naturally shortened. The speed is slow, the alcohol vapor pressure is low, and it is not easy to return to the tank through the reflux device for re-distillation, and the action time on copper is naturally lengthened. Fast or slow, shorter than longer is not good or bad, it all depends on the style required by the winery. However, wineries generally do not tell consumers the operating information, especially these technical details.
Take Glenfiddich and The Macallan, which are both located in Speyside and also use direct fire heating, as examples. The size of the distillers between the two is not much different.
Some of the Macallan data are not clear, but simply looking at the extraction time of the head, heart and total distillation time, it is obvious that Glenfiddich's distillation time rate is much slower, thus producing a clean, light body. , the style is very different from the imaginary direct fire heating. The Macallan not only heats up quickly, but its still has a short and fat shape, and the Lynn arm is 30 degrees downward. This is all to create a heavy-bodied wine. It is more suitable for direct fire heating.
In addition, comparing the relevant data of Ardbeg and Lagavulin, the distillers of these two distilleries are much larger than Glenfiddich. Of course, the time taken to extract the heart of the wine is also longer, but they use steam for indirect heating. The speed is obviously faster, and the firepower is increased when switching to the end of the wine, so that the overall time is not much longer than that of Glenfiddich. Obviously, even though Glenfiddich uses direct fire heating, the firepower is not strong, no wonder The wine produced is more light-bodied than powerful.
The knowledge of distillation is huge, and angels and devils are hidden in the details. For example, the extraction range of the heart of the wine will also have an impact. Although it is generally about 72% to 65%, each distillery is different due to its insistence on style. Take the two wineries mentioned above as an example. The heart of Glenfiddich takes 75% to 65%, while the head, heart and tail each account for 5%, 15% and 40%, and the remaining 14% is discarded. . The above ratio refers to the ratio to the loading, but strictly speaking, assuming that the alcohol content of low-alcohol wine is 30% after mixing the head and tail of the previous batch, then 1000 liters of pure alcohol will be 300 liters. . If 15% refers to the withdrawal of 150 liters of new wine, the real withdrawal rate is 105/300=35%.
Based on this calculation, the extraction rates of most distilleries are similar, but the time and cost of extraction are significantly different. Of course, they are also faithfully reflected in the head of the new wine. If consumers can deeply explore the details and think about various possibilities, , we can naturally dig out the truth behind the marketing rhetoric.
Comparison of differences in wine center cut points:
Each distillery has its own switching points between the head and tail of the wine. When the young and experimental Nantou Distillery makes peated whiskey, it has done a lot of cutting points in order to gain a deeper understanding of the differences that may result from the production process. Research. Both versions are distilled on the same day, placed in bourbon barrels, and then taken out on the same day. The only difference is the switching point between the heart and the tail. The extraction ranges are 74%~64% and 74%~62 respectively. %, after the trial drinking, the flavor performance was obviously different, which also confirmed the importance of the cut point.
