Understanding the Boil By: Tom Ayers

The Boil

 

Boiling your wort is an extremely important step no matter what level of brewer you are.  If you are an extract brewer this is where you and the all grain brewer join paths.  As an extract brewer the extract manufacturer has done the mashing and concentrated the wort down for you.  As an all grain brewer you have just wrapped up your sparge.  Either way you should have a kettle full of wort that is ready to be boiled down to the target original gravity. 

 Đun sôi dịch nha bạn là một bước vô cùng quan trọng không có vấn đề gì cấp của nhà sản xuất bia bạn đang có. Nếu bạn là một nhà sản xuất bia chiết xuất này là nơi bạn và các nhà sản xuất bia tất cả các hạt tham gia đường dẫn. Là một nhà sản xuất bia chiết xuất các nhà sản xuất chiết xuất đã làm việc nghiền và tập trung các wort xuống cho bạn. Là một nhà sản xuất bia các hạt ngũ cốc bạn vừa quấn lên tiết kiệm của bạn. Dù bằng cách nào, bạn nên có một ấm nước đầy wort rằng đã sẵn sàng để được đun sôi xuống đích lực hấp dẫn ban đầu.

Typically the boil should last at least 60 minutes, however depending on ingredients and the target beer it can last in excess of 120 minutes.  Boil time is critical to the end beer and it is important to understand how long you plan to boil so you can plan the starting volume.  For example, if you are targeting a post boil volume of 5 gallons and you average an evaporation rate of 9% per hour (which my system does) you should have around 5.49 gallons pre boil for a 60 minute boil but 5.78 gallons for a 90 minute boil.  Knowing the pre-boil volume is critical to sparging and boiling, but you must first learn your system and its evaporation rate. Programs such as Beer Smith give you starting points depending on your kettle. 

 Thông thường khi sôi nên kéo dài ít nhất 60 phút, tuy nhiên tùy thuộc vào thành phần và bia mục tiêu đó có thể kéo dài vượt quá 120 phút. Thời gian đun sôi là quan trọng đối với bia cuối và điều quan trọng là phải hiểu bạn có kế hoạch bao lâu để đun sôi để bạn có thể lập kế hoạch khối lượng bắt đầu. Ví dụ, nếu bạn đang nhắm mục tiêu một khối lượng bài đun sôi 5 gallon và bạn trung bình một tốc độ bay hơi của 9% mỗi giờ (trong đó hệ thống của tôi không), bạn nên có khoảng 5,49 lít đun sôi trước khi cho đun sôi 60 phút nhưng 5.78 gallon cho một 90 đun sôi phút. Biết khối lượng pre-đun sôi là rất quan trọng để sparging và đun sôi, nhưng trước tiên bạn phải tìm hiểu hệ thống của bạn và tốc độ bay hơi của nó. Các chương trình như Bia Smith cung cấp cho bạn bắt đầu từ điểm tùy thuộc vào ấm đun nước của bạn.

Of course the primary purpose of boiling and the reason it has been done for so many years is to kill wild yeast and bacteria.  This is, as all brewers know, critical to creating a clean and delicious beer.  If you don’t have clean wort going into the fermentor you will not have a clean beer coming out.  Additionally, if you did not do a mash out heating the wort towards boiling will stop all enzyme activity.

 Tất nhiên mục đích chính của sôi và lý do nó đã được thực hiện trong nhiều năm là để diệt nấm men tự nhiên và vi khuẩn. Đây là, tất cả các nhà sản xuất bia là biết, rất quan trọng để tạo ra một loại bia sạch và ngon. Nếu bạn không có wort sạch đi vào bình lên men bạn sẽ không có một bia sạch sắp ra. Ngoài ra, nếu bạn không làm một mash ra nóng wort hướng sôi sẽ ngừng tất cả các hoạt động của enzyme.

Of course as with everything in brewing there is more to the story.  The boil provides many additional benefits besides killing most anything in the wort.  The other critical thing the boil does is isomerize the alpha acids in the hops.  Alpha acids are the compounds in the hops that create bitterness (see hops article).  The longer the hops are boiled, the more IBU’s are contributed to the wort. 

 Tất nhiên là với tất cả mọi thứ trong sản xuất bia có nhiều câu chuyện. Đun sôi cung cấp nhiều lợi ích bổ sung bên cạnh việc tiêu diệt hầu hết bất cứ điều gì trong dịch nha. Điều quan trọng khác khi sôi thì là isomerize các axit alpha trong các bước nhảy. Axit Alpha là các hợp chất trong cây hoa bia tạo ra vị đắng (xem bài viết của hoa bia). Còn các hoa bia được đun sôi, càng Ibu của đang đóng góp vào dịch nha.

Hot break is typically what most brewers experience when they have a boil over for the first time.  As the boil begins the proteins in the wort begin to coagulate and build into a nice fluffy head and too often boil over the kettle.  As the boil continues the proteins will precipitate back into the wort and the head will dissipate.  It is important to have a good strong hot break to coagulate the proteins as it will assist in reducing haze.  

 Nghỉ nóng là điển hình mà hầu hết các nhà sản xuất bia kinh nghiệm khi họ có một luộc qua cho lần đầu tiên. Khi đun sôi bắt đầu các protein trong dịch nha bắt đầu đông lại và xây dựng thành một đầu lông đẹp và quá thường xuyên đun sôi trong ấm đun nước. Khi đun sôi tiếp tục các protein sẽ kết tủa trở lại vào wort và người đứng đầu sẽ tiêu tan. Điều quan trọng là phải có một break tốt mạnh mẽ nóng để đông lại các protein vì nó sẽ giúp làm giảm bớt khói mù.

Lastly, the boil is a great time to correct you gravity if you are off plan due to any variety of reasons including lower or higher efficiency than expected, lower or higher evaporation rates than expected, or any other reason that may cause your gravity to be off.  You can correct your gravity at any time, but the best time to do so is before the boil with after the boil a close second. 

  Cuối cùng, đun sôi là một thời gian tuyệt vời để chính xác bạn hấp dẫn nếu bạn đang tắt kế hoạch vì bất cứ lý do khác nhau bao gồm cả hiệu quả thấp hơn hoặc cao hơn so với dự kiến, tỷ lệ bốc hơi cao hơn hoặc thấp hơn so với dự kiến, hoặc bất kỳ lý do nào khác mà có thể gây ra lực hấp dẫn của bạn sẽ được tắt. Bạn có thể sửa trọng lực của bạn bất cứ lúc nào, nhưng thời gian tốt nhất để làm điều đó là trước khi đun sôi với sau khi đun sôi một đóng thứ hai.

Pre-boil Gravity Correction

Pre-đun sôi Trọng lực Correction

 At this point typically your efficiency is off from what was calculated in your recipe.  If you had poor efficiency your pre-boil gravity is lower than expected.  To correct this you can add DME (Dry Malt Extract) to the wort which will boost the gravity points or you can boil for longer than planned which will concentrate the wort further but result in less post boil wort than planned.  If you adjust your boil time, be sure to correct you hop additions to result in the same targeted IBU’s.  The reason gravity is so critical is recipes are often written with a target balance between IBU’s and gravity in mind. 

  Tại thời điểm này thường hiệu quả của bạn là tắt từ những gì đã được tính toán trong công thức của bạn. Nếu bạn đã có hiệu quả kém hấp dẫn trước luộc của bạn thấp hơn so với dự kiến. Để khắc phục điều này bạn có thể thêm DME (Extract Malt khô) để dịch nha sẽ tăng cường các điểm trọng lực hoặc bạn có thể đun sôi lâu hơn so với kế hoạch mà sẽ tập trung vào dịch nha thêm nhưng kết quả ít bài đun sôi wort so với kế hoạch. Nếu bạn điều chỉnh thời gian đun sôi của bạn, hãy chắc chắn để sửa bạn nhảy bổ sung vào kết quả trong cùng một mục tiêu của Ibu. Lý do lực hấp dẫn là rất quan trọng được công thức nấu ăn thường được viết với một sự cân bằng giữa mục tiêu của Ibu và lực hấp dẫn trong tâm trí.

Post-boil Gravity Correction

 Post-đun sôi Trọng lực Correction

If you have boiled and taken a gravity reading that is either too high or too low there are still way to correct for this.  It has most likely happened because your evaporation rate assumption was off.  If you have a gravity that is too high, you can add some water to dilute the wort to the gravity you are targeting.  Of course if it is too low you can add DME to boost the gravity or continue the boil.  I recommend taking a reading before you place your aroma addition in the boil.  The reason for this is if you need to continue the boil you should hold off on placing the aroma hop addition into the kettle until you are almost done with the boil.  If you do not and you continue to boil the aroma addition you will likely end up with a beer lacking any hop aroma because the boil will have boiled off the volatile essential hop oils.

 Nếu bạn đã luộc và lấy một bài đọc hấp dẫn đó là quá cao hoặc quá thấp vẫn có cách để sửa chữa cho điều này. Nó đã rất có thể xảy ra bởi vì giả định tốc độ bay hơi của bạn đã được tắt. Nếu bạn có một lực hấp dẫn đó là quá cao, bạn có thể thêm một ít nước để làm loãng dịch nha để lực hấp dẫn mà bạn đang nhắm mục tiêu. Tất nhiên nếu nó quá thấp, bạn có thể thêm DME để thúc đẩy sự hấp dẫn hoặc tiếp tục đun sôi. Tôi khuyên bạn nên dùng một đọc trước khi bạn đặt Ngoài ra hương thơm của bạn vào đun sôi. Lý do cho điều này là nếu bạn cần phải tiếp tục đun sôi, bạn nên giữ tắt về cách đặt các hương thơm hop Ngoài ra trong ấm đun cho đến khi bạn gần như được thực hiện với sự sôi. Nếu bạn không và bạn tiếp tục đun sôi thêm hương vị bạn có thể sẽ kết thúc với một bia thiếu bất kỳ hương thơm hop vì đun sôi sẽ bốc hơi các loại dầu thiết yếu hop dễ bay hơi.

One of the great things about brewing often with a consistent system is fully understanding your efficiency and evaporation rate. Once you hone in on these assumptions you will be able to hit

your targeted gravities throughout your process and hopefully have a nice smooth brew day with no adjustments required.

Một trong những điều tuyệt vời về sản xuất bia thường với một hệ thống nhất quán được đầy đủ sự hiểu biết của bạn hiệu quả và tốc độ bay hơi. Một khi bạn trau dồi tại trên những giả định bạn sẽ có thể đạt trọng lực nhắm mục tiêu của bạn trong suốt quá trình của bạn và hy vọng có một ngày brew đẹp mịn màng không có những điều chỉnh cần thiết.

Boiling: Advanced Brewing

Your bubbling boil doesn't have to cause trouble or toil. We'll show you how to get the most from this most basic of brewing procedures.

“Double, double toil and trouble; fire burn, and caldron bubble.” 

One aspect of the brewing process shared by nearly all brewers is boiling the wort. In fact, the symbol for brewing has long been the kettle used for boiling, easily the most recognizable feature of any brewery. In short, boiling is nearly universal and also important. It affects many of the qualities — gravity, color, bittering, flavor, purity and clarity, to name only the major factors — of the beer we brew. It’s worth investigating in some detail.

Boiling by the numbers

During the boil, some of the water evaporates, thereby concentrating the wort. The amount of evaporation varies with the size and geometry of the kettle, the surface area exposed to the air, the intensity of the heat source and to a lesser extent other variables such as the ambient temperature, humidity, air pressure and any movement of air surrounding the kettle.

For homebrew-size batches (5–15 gallons/19–57 L), the evaporation rate is normally measured in gallons (or liters) per hour, with typical values of 1 to 1.5 gallons (3.8 to 5.7 L) per hour. It’s worth experimenting to determine the average value for your brewing system. This requires a means of accurately measuring the kettle volume. You can scribe marks on the side of the kettle or make a “dipstick” by marking a tall spoon, rod or a dowel. Gradually fill the kettle with measured volumes of water and make the appropriate marks. Measure the volume both at the beginning and end of the boil and calculate the difference. Divide by the boiling time in hours to determine the evaporation rate.

For example, if the beginning volume is 7.5 gallons (28 L), the ending volume is 5.5 gallons (21L) and the boiling time is 90 minutes, the evaporation rate is 1.33 gallons (5.0 L) per hour:(7.5 gallons - 5.5 gallons) / 1.5 hours = 1.33 gallons/hour

Assuming the same kettle and burner are used, and that they are capable of maintaining an adequate boil, the boiling losses are largely independent of the batch size because the major factor is the surface area.

It should be remembered that the boiling point decreases with the altitude above sea level. At sea level and standard barometric pressure, water boils at 212 °F (100 °C). Although the formula is not truly linear, a reasonable rule of thumb for the altitudes at which most people live is to decrease the boiling point by one degree Fahrenheit for every 500 feet above sea level (one degree Celsius for every 300 meters). For example, in Denver, Colorado, at an altitude of 5,280 feet (1,609 meters), the estimated approximate boiling point is 201 °F (95 °C). [The more accurate calculated value, using the more complex formula, is

201.8 °F (94.3 °C).]

Hitting the target

If you know your boiling losses and the pre-boil specific gravity, you can estimate the post-boil original specific gravity (OG) of your beer with reasonable accuracy. The formula for calculating the approximate post-boil OG is:

Post-boil gravity points = (Pre-boil volume * pre-boil gravity points) / Post-boil volume

Specific gravity “points” (or GP) are the portion of the specific gravity reading to the right of the decimal point multiplied by 1000. For example, a specific gravity of 1.050 is 50 points.

Using the pre-boil and post-boil volumes from the example above, with a pre-boil specific gravity of 1.036, the projected post-boil OG would be 1.049.

(7.5 gallons * 36 GP) / 5.5 gallons = 49 GP (equivalent to SG 1.049)

Calculating the post-boil OG at the beginning of the boil is valuable because this is the easiest point to make adjustments. If the calculated OG differs appreciably from the target for the recipe, additional extract or water can be added. This subject is covered in detail in the July-August 2005 and January-February 2007 issues of Brew Your Own, but the following general rules may be of use to more relaxed brewers:

To increase the gravity of a 5-gallon (19 L) batch by approximately 1 GP at the end of the boil, add 2.5 oz. (72 g) — roughly one-half cup/118 mL — light dried malt extract, or approximately three-quarters cup (177 mL) liquid extract. To decrease the gravity of the same batch by approximately 1 GP, add 24 fl. oz. (710 mL) water prior to boiling. You can also manipulate the OG by changing the boiling time. In the above examples, a 9-minute increase in the boiling time will raise the OG by approximately 1 gravity point, while

decreasing it by 9 minutes will lower it by approximately 1 point. The approximate change in the post-boil volume per 9 minutes will be 22 fl. oz. (640 mL).

The bitter truth

Among the most important roles of boiling is to produce bittering in beer. While the heat dissolves hop resins, the alpha acids in hops are not initially in a form that is soluble in wort or bitter. They must first be isomerized, which roughly means re-arranged. Isomerization requires the heat and physical agitation of boiling over a period of time.

Of the total amount of alpha acids in a charge of hops, only a certain percentage is isomerized; the “hop utilization” depends on many factors but in almost no case exceeds 40 percent. For homebrewers, the net figure is typically in the mid-20 percent range for hops that are boiled 60 minutes. (This figure accounts for bitterness lost due to alpha acids adhering to foam during the boil or absorbed by yeast during fermentation.)

What you don’t want

Nearly as important as what is transformed and retained during the boil is what is evaporated and driven off. Pale malts especially contain sulfur compounds that can be transformed during fermentation into dimethyl sulfide or DMS, which has a noticeable vegetal aroma and flavor variously described as being like cooked corn, cauliflower or parsnips. DMS is undesirable in nearly all beer styles. Fortunately, DMS is volatile, and a vigorous boil evaporates it and drives it off into the air with the steam. (Heat also converts the DMS’s pre-cursor, S-methylmethionine or SMM, into DMS.) For this reason it’s important to leave the kettle mostly uncovered during the boil so the steam does not condense and return to the wort. If you do not have a burner with sufficient heat capacity for a rolling boil with the kettle totally uncovered, at least ensure that a significant open area exists in order for the steam to escape.

For all-grain brewers, boiling stops the enzyme activity that results in the conversion of malt starches to sugars. While the alpha-amylase enzymes that are the major factor in this process begin to be deactivated at 158 °F (70 °C), some conversion continues even to the beginning of the boil. Were the enzymes not destroyed completely, the additional conversion would result in a thin beer lacking in residual unfermentable sugars.

Moreover, boiling plays a major role in wort sanitation. In addition to any potentially harmful bacteria, boiling also kills wild yeast and other microorganisms that result in souring and undesirable flavors. Wort boiled for more than ten minutes can be considered sanitary. Further ensuring the safety of beer is the fact that alcohol produced by fermentation, as well as the acidity, also inhibits contamination. No known human pathogens (harmful microorganisms) can survive in beer.

Eat your protein

Homebrewers know that clarity is often a desirable quality, and also that any number of factors can cause the beer to be otherwise. Boiling is part of the solution to this problem. Malt contains proteins and compounds known as polyphenols are present in both the grain husks and hops. Some of these are necessary because they contribute to beer foam and an attractive head on the glass, but in excessive amounts they are a major cause of haze. Many of us have seen the chill haze that can develop when beer is refrigerated and the proteins flocculate (coagulate and become visible). Some of the same occurs when wort is boiled.

During the boil, the heat and agitation — both are necessary — causes the larger proteins and polyphenols to separate from attached water molecules and collect together. The phenomenon is clearly (pun intended) noticeable, and results in the hot break material that appears soon after the beginning of the boil. In worts with significant amounts of protein, such as those containing wheat, the appearance is pronounced, something like that of Chinese egg drop soup (which is caused by denatured egg proteins). Rather quickly (generally within 10–15 minutes) the wort, which has become cloudy as the boil begins, clears considerably, with large particles of hot break floating throughout.

To further assist in the coagulation of proteins and polyphenols, Irish moss is typically added during the last 15 minutes of the boil. Made from a type of seaweed that contains a polymer called carageenan, the moss has a negative electrical charge that is attracted and bound to the positively charged protein molecules.

Unless it is strained, much of the coagulated proteins, break material and Irish moss remain in the wort when it is chilled and transferred to the fermenter, but they are ultimately left behind when the beer is packaged, thus promoting the desired clarity. There is also some indication they provide necessary nutrients for healthy yeast reproduction.

Too much of a good thing

Almost every brewer has experienced the dreaded boilover. Seemingly within a matter of seconds, foam begins to collect on the surface of the hot wort, and the next thing you know it is climbing up and out of the kettle and onto the burner, sticking and burning and creating a mess to be cleaned up afterward. Another potential time for boilovers is during the addition of pellet hops. The tiny particles can provide nucleation sites for bubbles that cause foaming.

Learn to recognize the changes in the appearance of the wort as it comes to a boil. Keep a close watch on the kettle, leaving it uncovered at this point and turning down the heat somewhat at the first signs of agitation. Some brewers skim and discard the early foam, but all that is required is to gently stir the foam into the wort rather than allowing it to build up on the surface. Once a proper rolling but not excessive boil is achieved and the hot break material begins to flocculate, the situation becomes much less critical. Briefly

turning down the heat and stirring the wort well immediately after hop additions eliminates problems at those times.

Professional brewers control boilovers with a hose. Spraying water onto the surface of the wort as it begins to come to a boil helps to disperse the foam. Homebrewers can imitate this procedure with a clean garden hose sprayer or spray bottle filled with cold water.

How long?

Boiling times vary with the recipe and the beer style. Extract brewers are generally told to boil the beer for 60 minutes. Coagulation of the proteins in malt extract should occur within about ten minutes. However, the hop alpha acid isomerization necessary for bittering takes considerably longer; at 60 minutes more than 90 percent of this will have taken place. Boiling darkens the wort and the beer; reducing the boiling time will result in a lighter color. A far more important factor in determining color is the wort gravity, another reason to boil the full wort volume if possible, rather than boiling concentrated wort and diluting it with water in the fermenter.

Traditional brewing texts recommend that all-grain beers be boiled for 90 minutes, but my personal experience is that 60 minutes can be sufficient, especially for lower gravity and lighter colored beers. Reasons for a longer boil include the desire for higher wort gravity due to the greater evaporation, and also for flavor changes that occur and are desirable in some styles. Rich beers with complex flavors are often boiled longer.

When subjected to the temperature and agitation of boiling, complex reactions occur between sugars and amino acids, producing substances known as melanoidins. These are usually considered pleasant, resulting in flavors typically associated with the browning of meats and bread. Longer boiling times result in increased melanoidin production and are a major cause of wort darkening. It should be noted this is not quite the same thing as sugar caramelization, which requires higher temperatures and less water than what is present during boiling. Caramelization is part of the process that occurs during the production of crystal and other colored malts.

Sometimes the most reasonable way to produce high gravity wort for a strong beer is by means of a long boiling time. Using the formulas in the previous section on hitting the target gravity, you can adjust the time and calculate the gravity and volume accordingly. For example, if the evaporation rate is 1.33 gallons (5.0 L) per hour, a 120-minute boil of 7.5 gallons (28 L) will increase the pre-boil gravity from 1.070 to 1.108 and reduce the wort volume to 4.83 gallons (18 L).

Additional indications for a longer boiling time include brewing at high altitude where the temperature is lower (the undesirable volatile fractions take longer to evaporate), and situations where the boil is less vigorous than otherwise would be optimal.

What it all boils down to

Boiling is a very straightforward — but essential — brewing procedure. With a little knowledge and understanding of all the particulars and the procedures, you can be the master of your kettle and ensure that your beer is everything you want and more.

How to figure out your Evaporation Rate By: Kay Witkiewicz

Perhaps the most important aspect of your boil is knowing the evaporation rate of your brewing set-up in order to accurately match your pre-boil volume to your expected post-boil volume at the requisite specific gravity. While programs such as BeerSmith may give you an idea of your evaporation rate, nothing beats personal experience, and the only way to truly know your evaporation rate is to measure it in the act under your own brewing circumstances. Here’s how I figured out my evaporation rate, and it all starts with making a measuring device:

1.     Procure a dowel, a food-grade plastic spoon, or even a very long chop stick to serve as your measuring device. The three most important characteristics of the measuring device of your choosing are that it is the same height as or higher than your brewing kettle; it is an untreated piece of equipment, meaning the dowel isn’t lacquered, the spoon isn’t your usual sweet tea stirrer, and you didn’t eat take-out with the oversized chop stick last night; it can be carved into to mark certain volumes in your kettle.

2.     Take your brew kettle and a sizable container with a known volume (I use a one-gallon plastic container, but a very large measuring cup will also do) and head for your sink. Bring along a pocket knife and your measuring device as well.

3.     Fill up your container of known volume with water and pour its contents into your brew kettle. Repeat as many times as you need to in order to attain the beginning volume you want to mark on your measuring device.

4.     Place your measuring device into the same spot of your brew kettle (preferably the center) at volume increments of your choosing and carve a mark at each water line. For example, I know my brew kettle will never contain less than 3 gallons of wort pre- or post-boil, so the first mark on my measuring device is at 3 gallons with subsequent carvings at each additional gallon up to my brew kettle’s maximum volume of 7 gallons.

5.     Once you’re done marking all the volume increments that are convenient for you, you can either boil the water in your brew kettle for a set period of time and get an idea of your evaporation rate that way or you can just dump the water, wait until brew day, and figure it out as you’re boiling wort.

 

Notes: Carving is a precarious procedure, especially since your hands as well as your blade are likely to get wet during this exercise. However, I recommend carefully carving your measuring

device as it is a permanent means of marking with no potential impact on the flavor of your wort, whereas other means of marking, such as masking tape or Sharpie carry the risk of leaking unpleasant compounds into your wort when in contact with the hot liquid. The use of temperate tap water rather than steaming wort is another aspect to consider when making your own evaporation rate measuring device. Water obviously has a lower gravity than wort; moreover, liquid expands as it heats up. Therefore, when you immerse your measuring device in hot, or even boiling, wort, you will receive an upwardly skewed volume reading. While carving your measuring device relative to known volumes of hot wort would alleviate this inaccuracy, the splashing of wort is ultimately more detrimental to your beer than a slightly off volume reading.

 

Now that you have made your own evaporation rate measuring device, it’s time to put it to work. Useful in more ways than one, this handy stick tells me the volume of the first runnings of my mash and it allows me to gauge the amount of water I need to sparge with in order to hit my target pre-boil volume. Regardless of your brewing method, use it to measure your pre-boil volume of wort, then start your boil and temporarily measure the amount of liquid left in your brew kettle in order to judge the length of your boil necessary to meet your intended post-boil volume, gravity, and timing of your hop additions. If you’ve been brewing beer, but you haven’t actually measured your evaporation rate, chances are you have developed a good feel for it and the measuring device will only improve your brewing practices. If you’ve never paid attention to your evaporation rate, estimating your volumes, timing your boil, and figuring out when to add your hops can be daunting, but buck up and pay careful attention to how your brewing system reacts during your trial batch so you’ll have an intimate understanding of what you need to adjust for subsequent batches. Believe me, after collecting and fermenting more than a gallon more wort than I planned on for an American brown ale that also started 25 gravity points lower than expected, I knew that how much wort you’re boiling and how long you’re boiling it matters a great deal in executing your recipe, even though the beer turned out really delicious. Volumes and evaporation rate are neither as artisanally charming as grist composition nor as amazingly creative as hop additions, but they are fundamental to consistently brewing good beer.

Effect of Running Parameters on Flow Boiling Instabilities in Microchannels.

Flow boiling instability (FBI) in microchannels is undesirable because they can induce the mechanical vibrations and disturb the heat transfer characteristics. In this study, the synchronous optical visualization experimental system was set up. The pure acetone liquid was used as the working fluid, and the parallel triangle silicon microchannel heat sink was designed as the experimental section. With the heat flux ranging from 0-450 kW/m2 the microchannel demand average pressure drop-heater length (Δp(ave)L) curve for constant low mass flux, and the demand pressure drop-mass flux (Δp(ave)G) curve for constant length on main heater surface were obtained and studied. The effect of heat flux (q = 188.28, 256.00, and 299.87 kW/m2), length of main heater surface (L = 4.5, 6.25, and 8.00 mm), and mass flux (G =

188.97, 283.45, and 377.94 kg/m2s) on pressure drops (Ap) and temperatures at the central point of the main heater surface (Twc) were experimentally studied. The results showed that, heat flux, length of the main heater surface, and mass flux were identified as the important parameters to the boiling instability process. The boiling incipience (TBI) and critical heat flux (CHF) were early induced for the lower mass flux or the main heater surface with longer length. With heat flux increasing, the pressure drops were linearly and slightly decreased in the single liquid region but increased sharply in the two phase flow region, in which the flow boiling instabilities with apparent amplitude and long period were more easily triggered at high heat flux. Moreover, the system pressure was increased with the increase of the heat flux.

Dimethyl Sulfides (DMS) in Home Brewed Beer

Dimethyl Sulfide (DMS) is a sulfur compound produced during fermentation of beer that has the aroma of cooked or creamed corn. As part of my ongoing series on flavors in beer (including the earlier articles Esters in Home Brewed Beer and Judging Beer), we’re going to go into detail this week on DMS.

DMS in Home Brewed Beer

DMS (Dimethyl Sulfide) is a byproduct of mashing and fermentation, so it is present to some degree in all beers. It has the aroma of cooked or creamed corn. Because people can perceive DMS even at very low flavor thresholds (of 10-150 parts per billion) it can have a significant impact on the flavor of finished beer.

DMS is primarily found in lagers for a variety of reasons we will discuss shortly. DMS is actually desirable at low levels in many lagers, but excessive levels of DMS will create a strong cooked corn aroma and flavor. German lagers contain the highest DMS concentrations (50-175 parts per billion). American lagers generally contain less than 100 ppb, and British ales contain the lowest concentrations at 10-20 ppb. (Ref: Wikipedia).

Where DMS comes from:

All malt has in it a chemical called S-Methyl Methionine (SMM) which is responsible for DMS. SMM is an amino acid formed during germination and kilning of barley as part of the malting process. The maltster can reduce SMM by slightly under-modifying the malt, and adjusting the kilning temperatures, but this is largely outside the control of homebrewers. However, two row pale malts have significantly lower SMM levels than six row pale malts, so you can reduce your DMS levels by choosing a two row pale malt base. Also very pale lager malts (such as pilsner malt) tend to have slightly higher SMM levels due to the very low temperatures used in kilning.

Heating the SMM present in pale malt will always produce some DMS. During the mashing process (and even the boil), some SMM is broken down into both DMS and a variant of DMS called Dimethyl Sulfoxide (DMSO) which is basically DMS with an oxygen atom attached. So

after the mashing process we have wort that contains both DMS and DMSO (as well as some residual SMM).

The good news is that DMS itself is very volatile and a lot of it will boil off rapidly when we boil or wort during the brewing process. However DMSO is more stable, and some of it can be converted to DMS during fermenation. Vigorous ale fermentations generally produce less DMS.

Finally, infection can produce a DMS like flavor and aroma, though it will generally be an aroma closer to cabbage than corn. If you have a strong cabbage aroma or flavor you may have an infection in your finished beer.

DMS in the Beer Brewing Process

DMS is created whenever wort is heated, so some DMS is present in any beer. DMS is created in the mash, however most DMS is evaporated during the boil, so the boil is the primary place to focus if you have a DMS problem.

The half-life for DMS is 40 minutes, so half of the DMS will be boiled off in a 40 minute vigorous boil. So if we do the math, a 60 minute boil gets rid of 64.7% of the DMS and a 90 minute boil rids us of 79% of the DMS. That is why most experienced brewers recommend a 90 minute or longer vigorous boil.

Since DMS needs to evaporate off during the boil, it is important not to cover your pot. Covering a brew kettle during the boil will prevent the DMS from evaporating and create a beer with much higher levels of DMS.

Rapidly cooling your wort after boiling is also important. The SMM to DMS conversion continues at temperatures well below boiling, so DMS is produced even while the wort is cooling after the boil. However, unlike the mash, DMS produced while cooling cannot be boiled off. This conversion continues even if the hot wort is vented. For every hour you have hot wort sitting around, you will produce approximately a 30% increase in DMS.

During fermentation, CO2 bubbles actually help remove from DMS from the beer. More vigorous ale yeasts tend to produce lower DMS levels. Also different strains of yeast do tend to produce DMS during fermentation primarily by converting DMSO (which does not boil off) to DMS. Lager yeasts and yeasts fermented at lower temperatures tend to have higher DMS production. Certain wild yeasts and bacteria can create high levels of DMS as well.

DMS aromas (including some sulfur or rotten-egg aroma) during fermentation (particularly lagers) are not unusual, so you don’t need to toss your beer out just because you have a DMS aroma during fermentation. Some of this will fade naturally during the lagering process.

Finally, beers with robust flavor profiles (dark beers, strong ales, etc) tend to mask the DMS cooked corn flavor with other flavors such as roast, chocolate or caramel malts. Because of this, high DMS levels are most perceivable in lightly flavored beers such as low-adjunct pilsners,

many German lagers, continental lagers and extremely light ales. DMS is rarely a problem in beers that are Amber colored or darker, and also rarely an issue with most robust beer styles.

Controlling DMS – Summary

High DMS levels are most often perceived as a problem in light lagers such as Pilsner and many German lagers

Choose a 2 row pale malt (over 6 row) as a base malt to minimize SMM (a DMS precursor) Very pale base malts (such as pilsner malt) tend to have higher SMM levels which drives

higher DMS production Avoid using corn as an adjunct with these beers, as it can enhance the creamed corn

perception Boil your wort for 90 minutes or longer with a vigorous rolling boil Don’t cover your boil pot – leave it open so the DMS can evaporate during the boil Minimize hot wort standing time by rapidly cooling your wort after the boil Select a yeast and correct fermentation temperature to minimize DMS production For many lagers, DMS aroma is normal during fermentation, but it should fade with time as

you lager and age the beer

If you brew a beer with high DMS levels (creamed corn aroma) take a close look at the suggestions above, and focus on your boil, as that is where DMS can be most easily controlled. Thanks for joining me on the BeerSmith blog. Check out my podcast   or email list for more great brewing material!

Brewing Science: Controlling Diacetyl

Yeast is an amazing organism. It is responsible for producing bread, wine, distilled beverages, and beer. When yeast ferments beer, it produces more than 500 different compounds. Many of these compounds give beer its characteristic flavor and aroma. One of these compounds — one that is usually considered undesirable — is diacetyl.

Diacetyl gives a buttery, butterscotch-like flavor to beer. The flavor threshold of diacetyl — the level at which it can be perceived — is 0.1 parts per million (ppm) in “light” beer (such as Budweiser and Miller). Homebrewed beer can have levels from 0.05 to greater than 1 ppm.

Factors that influence the diacetyl level in beer are fermentation temperature, aeration level, bacterial contamination, and the yeast strain. Diacetyl levels vary during the course of fermentation and maturation. (See Typical Diacetyl Time Line, left.)

Fermentation ControlDiacetyl is a small organic compound belonging to the chemical group called ketones.

After yeast is pitched into beer, the yeast undergo a lag phase, followed by a phase of very rapid growth called the exponential growth phase. During both the lag and exponential phase, yeast build amino acids, proteins, and other cell components.

One of the amino acids produced by yeast is valine. An intermediate compound in valine production is called acetolactate. Not all of the acetolactate produced eventually becomes valine; some will leak out of the cell and into the beer. This acetolactate is then chemically converted to diacetyl in the beer. The chemical reaction is an oxidation, and high fermentation temperatures favor this reaction. The higher the temperature, the more acetolactate is converted into diacetyl.

Another factor that increases diacetyl production in this phase is insufficient nutrients. Valine is one yeast nutrient. Valine levels vary by type of malt. If there is not enough valine (or other yeast nutrient), the yeast will produce its own. But the more valine yeast produce, the more acetolactate intermediate is required, and hence the more diacetyl made. There is a strain-specific phenomenon here, because given the same conditions, different strains produce different levels of diacetyl.

The Stationary PhaseAs yeast slow down in fermentation, they enter what is known as the stationary phase. This phase is when beer undergoes a maturation process to develop the correct balance of flavors. One of the key elements of maturation is diacetyl reduction. Not only do yeast produce the precursor to diacetyl, they also consume the diacetyl that is produced and enzymatically reduce it. Yeast reabsorb diacetyl and convert it to acetoin and subsequently to 2,3-butanediol.

Acetoin and 2,3-butanediol have high flavor thresholds (they aredifficult to detect), and so neither contributes much in terms of flavor.

Give It a RestIt is important to provide sufficient maturation time for diacetyl reduction. This step is commonly known as a “diacetyl rest.” Diacetyl reduction is slower at coldertemperatures, so it is essential to incorporate the diacetyl rest when making cold-fermented lagers.

The process is simply to raise the fermentation temperature from lager temperatures (50° to 55° F) to 65° to 68° F for a two-day period near the close of the fermentation. Usually the diacetyl rest is begun when the beer is two to five specific gravity points away from the target terminal gravity. The temperature is then lowered to conditioning temperature following diacetyl reduction.

For ale production, the fermentation temperature is usually 65° to 70° F, so temperature modification is not necessary. But the fermentation should still be “rested” at this temperature for two days to ensure proper diacetyl reduction. Many brewers make the mistake of quickly crashing the fermentation temperature following terminal gravity. Why not? The beer is done, people are thirsty, and there is no taste of diacetyl in the beer.

Even though the diacetyl can’t be tasted, however, the beer might contain high levels of the precursor, acetolactate, which can be converted to diacetyl. Once the yeast is removed, there is no way to get rid of the diacetyl.

Caused by Contamination There is another way to get the buttery, diacetyl flavor in beer. This is the diacetyl contribution that brewers would rather not talk about: contamination.

Lactic acid bacteria, Pediococcus and Lactobacillus, produce diacetyl. These bacteria have historically been notorious contaminators of beer and are called beer spoilers. They are anaerobic and tolerant to alcohol and heat. This makes them happy to live in beer. The diacetyl produced by bacteria is far from pleasant and can taste like sour butter.

Small breweries and homebrewers have a difficult time bottling beer in a manner that eliminates lactic acid bacteria. This is one reason great-tasting beer can be bottled, only to develop pressure, sourness, and diacetyl flavors in as little as two months. What can be done? Sanitize well, bottle carefully, and leave some yeast in suspension. This yeast won’t kill bacteria, but it will reduce any diacetyl produced from oxidation of acetolactate in the bottle.

Inviting Diacetyl?Most brewers do not like the presence of diacetyl in their beer because it is a hint of a possible fermentation or contamination problem. But some brewers desire their beer to contain diacetyl in the final product. For example Redhook ESB has a characteristic diacetyl taste. This is most likely produced from the yeast strain used or from the fermentation profile employed.

Some yeast strains, particularly flocculent English ale strains, are known to be heavy diacetyl producers. Alternatively, the fermentation temperature can be crashed following terminal gravity, which would prevent the diacetyl rest from taking place. Low levels of diacetyl produced in this manner can be pleasant, and many classic beer styles such as Scotch ales and bitters allow for low levels of diacetyl to be tasted in the beer.

Diacetyl Formation Facts

Some yeast strains produce a lot of diacetyl, while others produce less. Choose yeast that produces less, unless you are brewing a style that allows for the presence of diacetyl.

High fermentation temperatures promote diacetyl production. Low aeration levels when yeast is pitched will produce less healthy yeast, which are

prone to higher diacetyl production. Ale fermentations produce more diacetyl because ales are fermented warmer than lagers,

but the reduction happens much quicker. Lager fermentations need to be given a “diacetyl rest” by increasing the fermentation

temperature just before completing fermentation. A hydrometer should be used to measure the specific gravity to calculate when to start

the diacetyl rest. Begin when the beer reaches two to five points of final gravity. The fermentation should never be rushed. Give the beer ample time for maturation.

Sanitize well, particularly when bottling, to limit the effect of diacetyl from bacterial contamination.

My beer sometimes has a corn-like sulfury smell. What can I do about it?

A corn-like smell is usually due to a specific chemical compound called dimethylsulfide, or DMS for short. DMS forms in the malting process and in the boiling process while brewing any beer. It is the result of a thermal degradation of sulfur-containing amino acid in the grain called s-methylmethionine. This amino acid is present in all malts. Hence, all beers have some amount of DMS.

DMS is a highly volatile compound. This makes it an easily detectable compound in aroma, even in trace quantities. Fortunately, the volatility makes it fairly easy to scrub out of your beer.

The amount of DMS in your finished beer depends on a number of factors. First of all is the amount of s-methylmethionine in the grain. High protein malts such as six-row have higher amounts, hence more DMS. Some of the DMS is driven off by heat in the kilning process. Hence, the paler malts kilned at lower temperature have more. These two factors combined contribute to the fact that pale lagers (made from pale six-row malt), often have high levels of DMS. Not surprisingly, corn also contains a lot of s-methylmethionine. These characteristics are a hallmark of lager beers. A lager without DMS tastes rather bland.

The second factor that affects the amount of DMS is how much is removed from the wort during the boil. Every bubble of steam that comes out of the kettle will carry some DMS with it. Hence, longer boiling times and a more vigorous boil tend to reduce DMS levels. For best results, you want to keep the boil rolling for the whole time. Don't simmer your beer.

The third factor that affects DMS levels is the rate at which the beer is cooled. The decomposition reaction that converts s-methylmethionine to DMS is driven by heat. Once you shut off the heat and start cooling the wort,

scrubbing action of the steam is halted. However, DMS continues to be formed until the wort is below about 160oF. Hence, a long steep will increase DMS.

The final factor (usually) is the amount of DMS that is scrubbed out during fermentation. Carbon dioxide bubbles will remove some of the DMS. Since more CO2 comes off at higher temperatures, more is scrubbed out of ales than lagers. Well-attenuated beers will be more scrubbed as well.

The plot to the right illustrates the potential DMS levels in your beer. Here we assume a 90 minute boil, a 60 minutes whirlpool at flame-out, followed by cooling and fermentation. The level of s-methylmethionine drops the longer the boil goes. The amount of DMS can rise potentially to the ending level of s-methylmethionine at flame-out if the wort isn't chilled. Conversely, a rapid chill would lead to almost zero DMS.

If you're not too careful about sanitation, you'll find that some bacteria also contribute to DMS levels. Coliform in particular is known to produce DMS. Generally, though, it will also produce other foul odors such as mercaptan (natural gas smell) and hydrogen sulfide (rotten egg smell), making the DMS level the least of your worries.

Generally, if you keep your boil vigorous and cool rapidly, DMS levels will be appropriate for style. However, the DMS level may still be too high for your taste. If you keg your beer, you can artificially scrub out DMS using CO2. This is best done before carbonating. If you have a lager, allow it to warm to room temperature first. Then, switch around the ball-lock fittings on your keg so they are backwards. Hook up the long dip tube (labeled "out") to the CO2 tank. Prop open the pressure relief and let the CO2 bubble through the beer. Slow down if it starts to foam out. Occasionally sniff the gas as it exits the keg valve. You should be able to smell the DMS at first, and then notice it fading with time. After the level has dropped, switch the ball locks back to their usual configuration. Then carbonate as usual.

Coltrol of Dimethyl Sulfide (DMS) During Brewing ProcessDuring the brewing process a number of volatile compounds are extracted from malt, hop ant other raw materials. Some of these persist or are modified during the fermentation to produce the characteristic flavor of the beer. DMS (dimethyl sulphide) is the most important flavor active compound found in malt.

DMS is a water-insoluble flammable liquid that boils at 37 °C and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize, cabbage, beetroot and seafoods.

DMS mainly exists as its precursor SMM (s-methyl methionine) which is decomposed on heating to produce DMS. When this happens during boiling the volatile DMS rapidly flashes off, but should the precursor continue to breakdown after boiling, for example in the wort clarification stage or in the hot wort prior to cooling, when there is limited loss of volatiles and the DMS flavors will be carried forward to the finished beer.

To controlling DMS it is necessary to reduce the duration of the hot stand (whirlpool and cooling time) to reduce the amount of volatile DMS produced which cannot then be lost by evaporation. Some breweries use either hot or cold wort stripping to flash of the residual DMS by bubbling air through the wort.

DMS is also an indication of bacterial infection in malt production and brewing. It is a breakdown product of dimethylsulfoniopropionate (DMSP), and is also produced by the bacterial metabolism of methanethiol.