Mr. Wizard

What Don’t I Know About the Pros?

Dear Mr. Wizard,

I have been homebrewing for several years and have read quite a bit about homebrewing from books and magazines. The other day, a buddy and I were sitting at a brewpub, having a pint and talking about beer and brewing. Looking at the brewing equipment behind the glass, it wasn’t too hard to figure out what the vessels were for. So my buddy asked me if I could jump back there and brew one of my beers. I had to admit that I didn’t really know. I’ve always assumed that commercial brewing was just a “bigger” version of homebrewing, but I didn’t know for sure. I know that many commercial brewers do steps that most homebrewers don’t, such as filtering or pasteurization. But, do homebrewers make beer fundamentally the same way as brewpub brewers, or as large commercial brewers?

Randy Decker
Altoona, Pennsylvania

Mr. Wizard replies:

In a very generalized sense, all beer is made using the same basic steps. All beer begins as wort that is then fermented, aged, clarified to some extent and packaged. The biggest difference between what is done at home versus in a big brewery is the equipment used. Commercial brewers use multi-roll or wet milling to crush their grains. Wet milling can be performed more than one way, but most wet mills these days have a steeping tank above the mill where malt is sprayed with water to increase the moisture content of the husk. After the malt passes through a single set of rolls it is hydrated with mash water and the mash is then pumped directly to the mash mixer. Many breweries use adjuncts like rice and corn and these are often milled using special mills.

Mashing is basically the same process, except most commercial breweries use steam-heated mash mixers with special agitators that help keep the mash uniform in temperature while at the same time not beating up the malt so that wort separation runs smoothly. Brewers who use adjuncts have to boil the adjunct in order to gelatinize the starch and it is common to have a cereal cooker and a mash mixer when adjuncts are involved. In fact, this set up is basically the same as a decoction brewhouse that has a decoction kettle and a mash mixer. One big difference in the whole mashing and lautering steps is that ingredient yield is closely monitored. Most commercial breweries achieve at least 92% of laboratory yields and many breweries are pushing yields that are nearly equal to the theoretical laboratory yield.

Most American breweries use lauter tuns to separate wort from malt solids while some use mash filters. Lauter tuns used in commercial breweries have slow moving rakes that gently cut through the grain bed to facilitate wort separation and then the same device is used to move the spent grains out of the lauter tun and into a pump that takes the grain to a spent grain storage area.

Some smaller breweries, especially pub brewers, use infusion mash tuns for mashing and wort separation. This is much more akin to what is done at home. It is common for the brewer to use a mash paddle when mashing in to evenly lay down the mash and to use some sort of hoe to remove the spent grains from a door in the side of the mash tun after mashing is complete. Then the plates are removed and the mash tun is given a good cleaning. There is a lot of brewpub equipment that actually grew out of homebrew equipment.

Mash times are similar. In fact many pub brewers mash-in, take a short breather and begin wort collection. My old professor from University of California-Davis is the one who started pushing this idea. The reason it works is that there is no mash-off step and as long as the wort collected in the kettle is not prematurely heated, conversion of starchy worts continues in the kettle during wort collection and the amylases in the mash are active during almost the entirety of sparging. Brewers doing this use much shorter mash times.

Wort boiling also uses different equipment because of the much larger batch sizes. Small pub operations use either steam heated or flame heated kettles that are not much different than a big pot with an external heating jacket. As kettles get larger than about 1,000 gallons (3,800 L), more heating surface is needed than that available on the exterior of the kettle. Internal or external heat exchangers called calandrias are used to increase the heating area and the boiling wort exiting the calandria is directed to a wort spreader (the cone-shaped “hat” seen on top of the giant kettles) that fans wort out over the surface of the boiling volume. This helps to knock down foam as well as creating a large surface area for DMS to evaporate and exit through the kettle stack, or exhaust pipe. Some kettles are even pressurized and other designs cycle the pressure up and down to create uniform, nucleate boiling periods when the pressure is released. Most commercial breweries boil for 60–90 minutes, even with some of the newer kettle designs. The trend, however, is towards reduced evaporation rates. The old standard was 8% per hour and many new kettles are being designed for a total evaporation of 4% or less. Certain laws in Europe are really driving this because of energy penalties being imposed on breweries who buy new equipment designed for high (>4%) evaporative rates.

Hop separation is also different for commercial brewers because of the larger batch sizes. Most beer these days is made using hop pellets and these can be separated in large whirlpool vessels. Homebrewers can also use the whirlpool method to help separate hop pellets and trub from yeast. Breweries using whole hops typically use a hop separator that strains the hops from the wort and continuously augers the spent hops out of the device. Smaller brewers use hop backs that look very similar to a mash tun.

Finally, the wort is cooled using a plate heat exchanger with enough surface area to cool down the batch in anywhere from 30–60 minutes. This means that the hot wort sits in the whirlpool vessel for a fairly long time. After cooling, wort is aerated in-line with either filtered air or oxygen and then flows into the fermenter. Many brewers inject yeast in-line after aeration and others put the yeast in the bottom of the fermenter where it mixes with the wort.

I would say that wort production in a commercial brewery is pretty darn different than the way most homebrewed wort is made, either with extracts or all-grain mashing. When it comes to fermentation and aging, however, the process is pretty similar. One big difference is that larger brewers typically ferment 4–6 batches in the same fermenter and various techniques of yeast pitching and aeration are used when a tank is filled over the course of 12–18 hours.

Another notable difference used by the largest breweries is the use of a technique called high gravity brewing. This means that high gravity wort, usually between 14–18 ºPlato (1.056–1.072 SG), is fermented and later diluted with deaerated, carbonated water. The reason big breweries do this is to reduce their fermentation requirements by up to about 33%. Craft brewers typically do not use this method.

Aging is not much different at home unless we are talking about the King of Beers and the use of beechwood chips in their chips tanks. Anheuser-Busch is the only brewery that I know of who still uses this once not so uncommon technique.

Next comes filtration and there are all sorts of methods used by commercial brewers to clarify beer. Diatomaceous earth (DE) pressure leaf filters, DE plate and frame filters, centrifuges and sheet filters are the conventional methods. Many brewers use chill-proofing agents, such as silica hydrogels and PVPP, at the time of filtration to protect against chill haze and some brewers add isinglass finings before filtration to improve filter run times. The most modern filtration method is cross-flow membrane filtration and the aim is to eliminate the use of DE in beer filtration.

Some commercial breweries even recover beer (called ruh beer) trapped in the yeast cake. Not only does this reduce beer losses associated with spent yeast but it also reduces effluent. This method is not practiced by the majority of commercial breweries in the U.S. because the quality of the beer may easily suffer due to yeast autolysis.

The last step is packaging beer into bottles, cans or kegs. Most large breweries pasteurize their bottles and cans in a tunnel pasteurizer after filling to kill any spoilage organisms that may be in the beer. Some draft beer is flash pasteurized like milk before kegging.

As a general rule, craft-brewed beer made in the United States is not pasteurized. There are a few craft brewers out there who do have pasteurization equipment, but these are the exceptions. There is nothing wrong with pasteurization when done correctly, but it does prevent beers to be bottle conditioned because it kills the yeast.

Simply put, homebrewed beer and commercially brewed beer start with the same basic ingredients and may taste very similar when poured into a glass, but they arrive at that point by very different paths.

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Hot and Bothered About Temperature Differences

Dear Mr. Wizard,

I was pouring a homebrewed Belgian wit today and I was wondering if I was about to enjoy the fruit of my labor at the proper temperature. I measured the temperature with a recently calibrated thermometer at approximately 50 ºF (10 °C). Typically, I keep my converted chest freezer at approximately 38 ºF (3.3 °C) using a refrigerator thermostat and I monitor the temperature with an accurate commercial grade thermometer. I ferment in another converted chest freezer using the same method of temperature control. The 12 ºF (6.7 °C) difference in temperature raises several questions. Are there variations between fermenting wort/beer temperature vs. ambient temperature? What, if any, affects will these temperature variations have on my finished product? Are the recommended temperatures by yeast labs suggested for wort/beer temperature or ambient temperature? Please enlighten me.

Thomas Crawford
Tallahassee, Florida

Mr. Wizard replies:

I want to clarify my understanding of your question. Your question is about fermentation temperature and this question came to you when you were pouring your wit. I will address this question, but first want to comment on what may have happened with the wit you poured. Let’s assume that both of your thermometers were reading correctly and the refrigerator temperature was indeed 38 ºF (3.3 °C) and the beer temperature after pouring was 50 ºF (10 °C). Obviously, there are only two things that may have been responsible for this difference in temperature. The first is that the wit was not refrigerated for long, had not equilibrated with the refrigerator and was warmer than 38 ºF (3.3 °C). The second possibility, which most likely occurred to some extent, was that the glass you poured the wit into was warmer than 38 ºF (3.3 °C) and it warmed the wit.

Based on an assumption about the specific heat of glass, I calculate that a glass beer mug weighing 32 oz. (900 g) could warm beer from 38 ºF (3.3 °C) to 50 ºF (10 °C) if the glass was originally at 72 ºF (22 °C). This is not a very unusual scenario and explains why some bars used those awful frosted mugs for beer. Tossing a mug in the refrigerator before use prevents this heating affect from occurring and does not turn your cold beer into a beer slushy like a frosted mug.

The real question you have is about differences between the fermenting beer in your carboy and the air temperature of the refrigerator. Heat is produced by yeast during fermentation and is removed by the surrounding air. In all cooled systems, the difference in temperature between the thing being cooled and the cooling medium drives the rate of cooling. (The same is true of heated systems.) As the temperature of the two components of the cooling system approach each other, the rate of cooling slows. When thickness is added to this argument, a temperature gradient between the core of the body being cooled and the surface of the body is seen. If the body is solid, the mode of heat transfer is called conduction because the heat is conducted through the solid. In liquids things get a bit more involved since the liquid moves and this movement sets up convection currents.

Applying this rule to a fermenter of beer, you can see that the center of the fermenter will be warmer than the surface and that stirring the fermenter will increase the rate of heat transfer through convection. Although beer fermenters are not usually stirred using a mixer, there is considerable movement caused by the release of carbon dioxide from fermenting beer. In any case, there is a temperature gradient in a beer fermenter and the temperature at the surface is typically cooler than the temperature within the fermenting beer.

At home this difference is small because the volume of liquid is small and the surface to volume ratio is large. In larger fermenters, the surface-to-volume ratio decreases and the temperature gradient within the fermenter can become significant. When yeast companies suggest a certain fermentation temperature for a certain yeast strain, they are referring to the temperature of the fermenting beer, not the air temperature of the surrounding environment. However, in a small fermenter such as a 5-gallon (19-L) carboy the difference between the air temperature and the beer temperature is usually within about 5 ºF (3 °C). So if you have a yeast strain that produces the best beer when fermentation is held at 70 ºF (21 °C) the surrounding air temperature should be around 65 ºF (18 °C). You can periodically monitor this by inserting a thermometer into the fermenting beer.

In larger fermenters, a cooling jacket is used because air cooling is ineffective and the fermenter becomes way too warm. A cooling medium such as propylene glycol (food-grade anti-freeze) is pumped through the cooling jacket and the heat added to the glycol coolant is then removed using a refrigeration system. (Even though the anti-freeze does not touch the beer, the jackets can develop leaks and anything in a food plant used as a coolant must be food-grade in the event of a leak.) These larger fermenters are typically equipped with a valve that opens and closes in response to the temperature of the beer inside of the tank. Simple systems use “on/off” control and the beer temperature fluctuates around the target temperature. The difference between the target, 70 ºF (21 °C) for example, and the temperature where the valve opens or closes is called a dead-band. Most simple controllers are set up to control the beer within a 2 ºF (1 °C) dead-band around the set-point and the beer temperature is constantly moving within this 2 ºF (1 °C) dead-band around the set-point.

More sophisticated control systems employing proportional control valves and PID controllers (proportional, integral and derivative control is a mathematical-based control scheme to achieve much tighter process control) greatly reduce temperature fluctuation around the set-point value and in many cases can match the actual temperature to the set-point value over long time periods.

Where I work, we have on/off control and operate on a 2 ºF (1 °C) dead-band. The key, in my opinion, is having some target and being consistent in controlling around that target. When it comes to fermentation temperature, it is important to have a target fermentation temperature and have some method to achieve the goal. Absolute accuracy is less critical than having a target and a plan of action. If you allow the temperature to get too far off course, you will most likely see the effect of temperature of the fermenting beer. If it is warmer than planned, expect accelerated fermentation rate and the production of more esters. An overly cool fermentation may be very sluggish and it may fail to properly attenuate.

The key with most brewing is to keep it simple. There is absolutely nothing wrong with relying on the ambient temperature of your chest cooler to control fermentation temperature. Just remember that the temperature of the beer in the carboy will never be the same as the air temperature as long as the yeast is producing heat. This means that temperature of the wort will increase as yeast begin to ferment. When activity peaks and the rate of fermentation wanes, the temperature will begin to drop and will eventually equilibrate with the ambient temperature of your cooler when fermentation ceases. If you measure the temperature of the fermentation, you can get a good feel for where your thermostat should be adjusted.