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Controlling Fermentation Temperature

What is the most basic and critical factor that drives the fermentation of your beer? Obviously, the yeast. Did you realize, though, that the temperature at which fermentation occurs will dramatically affect the flavor of your beer?
Each yeast strain has a narrow range of temperatures at which the ideal fermentation will occur. Too warm, off-flavors will be formed in the beer. Too cold, fermentation will not be vigorous enough to complete.
When I started home brewing beer I was letting it ferment in the hallway of an apartment without air conditioning, in the middle of summer, at temperatures of 80 to 85 degrees. I did not realize at the time that this is what was causing my beer to have some funky off-flavors.
The ideal fermentation temperature for most types of ale yeast is in the mid-60’s Fahrenheit (lager yeasts like it cooler). In many areas it is difficult to keep fermenting beer at this temperature because it is too hot in the summer or too cold in the winter.
Even with forced air heating or cooling your house, there is likely to be a several-degree swing in temperature
There are some tricks that can be used to help the beer ferment at a steadier temperature, though:

Keeping Beer Warm Enough

Carboy Parkas

If you have to ferment you beer in a basement or garage in the winter (I’ve even had difficulties in an unused spare bedroom in the winter) you likely will not have the sufficiently warm 65 degree ambient air temperature that you need.
A simple way to keep your fermentor warm enough (if you are fermenting in a carboy, rather than a bucket) is a carboy parka. These come in many different variations, but they are always a fitted cover that is meant to provide insulation to reduce temperature fluctuations.
These work especially well because the process of fermentation will naturally heat up the vessel, in some cases as much as ten or fifteen degrees, and the parka will keep this warmth in. Carboy parkas also have the benefit of blocking out harmful UV rays from the beer.
Some carboy parkas are really basic, and some nicer ones (like the one pictured below) are made of a more insulated material and come with handles for moving the carboy easily.

Electric Carboy Parka with Handles

Electric Carboy Heaters

If a carboy parka just isn’t enough to keep your beer up to fermentation temperature then an electric carboy heater (like the one pictured below) is the way to go. These are simply electric heater pads that hook up to a temperature controller to keep your beer at a very specific temperature. They can be used on glass, plastic, and metal fermentors.There is not any guessing involved about the temperature, like there might be with a carboy parka. Electric carboy heaters will keep your fermentor warm enough no matter the conditions.

Electric Carboy Heater

Keeping Beer Cool Enough

Swamp Coolers

The most basic method of keeping a fermentation vessel cool enough in hot temperatures is commonly referred to as a “swamp cooler.” This term refers to keeping the fermentation vessel in a tub of water filled up at least to the level of the beer in the fermentor. Since water is more resistant to temperature change than air, it will not heat up as quickly or cool off as quickly as the air in the room. A floating thermometer can be placed in the swamp cooler, or an adhesive thermometer label called a Fermometer can be placed on the outside of the fermentation vessel to monitor temperature.
Even outside of avoiding temperature extremes, it is easier to control the temperature of the fermentation when the fermentor is surrounded by water. If the water is too warm it is easy to add ice or a frozen bottle of water to cool it off. It is even possible to set up a pump to circulate water from a tub of ice water into the swamp cooler. The pump can be activated by a temperature probe if the water in the swamp cooler gets above a specified temperature .
If it is difficult to keep the fermentor cool enough you can also wrap it in a towel, with just the bottom of the towel touching the swamp cooler water. The towel will wick water up to cover the fermentor, and as the water evaporates away it will naturally cool the fermentor. For an added boost to the cooling, place a fan nearby and have it blow past the vessel to encourage more rapid evaporation.
If the water in the swamp cooler gets too cold, an aquarium heater can be dropped in to heat it up.
Swamp coolers are a great option if you are looking for a way to automate temperature control without committing a lot of money or space to a converted chest freezer (see fermentation chambers, below).

Fermentation Cooler Bags

A simple alternative to swamp coolers are Fermentation Cooler Bags, like this one, that are essentially the cooling version of a carboy parka.
Cooler bags are made of heavy-duty insulated material into which you place your fermentor and bottles of frozen water. Each one-liter bottle of ice will typically cool the fermentation temperature by about five degrees Fahrenheit, down to about 30 degrees below the ambient room temperature.

Fermentation Cooler Bag

Fermentation Chambers

A more sophisticated method of stabilizing fermentation temperature is to build a fermentation chamber.

Most fermentation chambers are built from an insulated container such as an old refrigerator or freezer. A temperature controller is used to regulate the temperature of the chamber. If the chamber is kept in a cold area, such as a garage, a heater may actually have to be placed in the chamber to keep it from getting too cold.
Monitoring the temperature of your wort in a fermentation chamber is a little more tricky than doing so in a swamp cooler. The wort will heat up and cool down more slowly than the air in the chamber, so to obtain a more accurate reading you need to either add a temperature probe to the wort, or add a probe to a container of water that is also in the chamber to mimic the wort temperature.
A nice piece of equipment that will help regulate your fermentation chamber is a switch that can be activated by a temperature probe. When the temperature in the chamber falls outside of the specified range the switch will activate either the refrigerator or the heater as necessary.
Have you tried any other methods of controlling fermentation temperature? Tell us how they worked for you in the comments below!
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8 Quick Questions About Aged Hops and How to Age Hops

Aged cheese, aged wine, aged liquor…aged hops? When and why would you used aged hops?

1. What Are Aged Hops Used For?

Aged hops are used in beers that are spontaneously fermented, which means that they are exposed to open air to allow natural yeast to enter the wort and ferment it. No yeast is added by the brewer. These beers are fermented in wood barrels for at least a year, sometimes several years, and take much of their flavor from the wild yeast and bacteria that enter during the open-air exposure and that exist in the wooden barrels.

This style of beer, known as Lambic, is not known for its hop bitterness. Its unique, sour flavor actually requires minimal hop bitterness. When hops are aged they lose their bittering properties, but they do not lose their ability to prevent infection in the beer. This is why aged hops are perfect for brewing Lambic: they protect against wild bacteria infecting the batch, but they do not give the beer much bitterness.

2. How Are Hops Aged?

Hops are aged by simply letting them sit in a dry place, such as an attic, for one to three years. Home brewers most often place the hops in a brown paper bag and then leave them to age.

3. Why Do Hops Have to Be Aged for So Long?

As the hops age they go through phases that are described as “funky” and “cheesy” due to their aroma. After sufficient aging, though, the hops will lose any aroma and flavor that they once had. A full year of aging will diminish flavor and aroma in most cases.

4. What Type of Hops Are Aged?

Whole leaf hops are used for aging because hop pellets do not age quickly.

Some sources recommend aging hops that are low in alpha acid, which is what causes the bitter flavor in hops. Essentially any variety of hop can be aged, however, because the goal is to rid the hops of flavor and aroma anyway.

5. Is There A Way to Accelerate Hop Aging?

You can rapidly age hops by heating them to 150 degrees F in an oven for up to twelve hours, but with a caveat: it will make your house smell horrible and the smell may linger for days!

6. Is There An Alternative to Aged Hops?

If you are brewing a Lambic but can not find aged hops, or do not want to wait a year or two for them to be ready, there is another option. Replacing the aged hops in your recipe with a very low-alpha acid hop variety will give similar results. If you do this, aim for a final bitterness between 10 and 15 IBUs for the beer.

7. How Many Ounces of Aged Hops are Necessary for a 5 Gallon Batch?

Recipes vary, but Lambics often use 3 to 4 ounces of aged hops. If the Lambic is going to become a fruit beer even fewer hops are used – only 1 or 2 ounces.

8. Where Can I Buy Aged Hops?

Try these home brewing suppliers for aged hops:

Hops Direct
Seven Bridges Cooperative

Have you ever aged hops? What process did you use and how did it turn out?

Simple Advice from a Home Brewing Professional

Last week I was in my local home brewing supply store asking an employee about the finer points of a specific brewing process that I was about to try for the first time.

He gave me a very non-specific, but helpful answer.

“For hundreds of years illiterate Germans were able to brew incredible beer by throwing hot stones into wood vats to boil wort. They didn’t even know what yeast was. Just try things out and you will be ok.”

So, there you have it. Sometimes we need to stop thinking so much about making beer, and just make beer!

4 Questions and Answers About First Wort Hops

A slightly advanced technique that you might come across if you begin brewing using “partial mash” or “all grain” techniques is called “first wort hopping.” This is a technique that caught me off guard when I bought my first partial mash kit – good thing I actually read the instructions for that brew!

What Are First Wort Hops?

“First Wort Hopping” refers to adding hops to the boil kettle and then running the wort in on top of them as you sparge. This all takes place before the boil, where you would normally add the hops. This is actually an old technique that was re-discovered in the last twenty years.

Why Use First Wort Hopping?

There are two big advantages to first wort hopping: it increases the overall bitterness of the beer by about ten percent without adding extra hops, and it produces a more uniform bitterness rather than a “sharp” flavor. Both of these changes take place because the hops are added when the wort is hot but not yet boiling. This causes some processes to occur within the wort to increase hop utilization and prevent some of the more aromatic oils in the hops from boiling off.

What Hops Are Best For First Wort Hopping?

Hops that are low in alpha acid work best as first wort hops because they do not cause a sharp increase in bitterness. Instead, they enhance bitterness while producing a smoother flavor and smell.

Most sources recommend using about 30 percent of your hop schedule as first wort hops. Some say to simply move your first hop additions from the beginning of the boil to the first wort hopping phase, but most (including John Palmer) recommend taking the hops from your late (“aromatic”) hop additions. The later hop additions are typically lower in alpha acid and work better as first wort hops.

What Beer Styles Should Utilize First Wort Hops?

The best styles for using first wort hops are those that emphasize the hop profile of the beer. Typically this includes pale ales, IPAs, ESBs, and some pilsners, but experimentation can be done with other styles. I have even heard of first wort hops working well in Belgian tripels and wit beers.

Do you have any experience with first wort hopping? How has it worked for you?

What is Belgian Lambic Beer?

In our last post we took a look at “sour” beers. One of the beer styles that is most often made into a sour is the Belgian Lambic. This beer, with a dry flavor and sour aftertaste, is not very common, so you might not know much about it.

What Makes Lambics Distinctive?

Belgian Lambic beers are only made in one small area: in the Senne Valley of Belgium, southwest of Brussels. The most significant characteristic of Lambic beer is that it is fermented “spontaneously,” meaning that the beer is brewed and then exposed to open air for a time to allow the yeast and bacteria naturally floating in the air of the Senne valley to enter the beer and start the fermentation. Yeast is not added by the brewer as a part of the brewing process.

The bacteria naturally occurring in this region, including strains of Brettanomyces yeast, are what give Lambics their distinctive flavor. Lambic can only be brewed in the colder months of the year, from October to April. The air during the summer months contains too many strains of bacteria that would be detrimental to the beer.

In addition to the open-air fermentation, the beer is aged for one to three years in wood barrels made from oak or chestnut and which had previously aged port, sherry, or wine. This provides even more wild bacteria from the wood to condition the beer. It has been found that Lambics contain more than eighty different bacteria due to these fermenation and aging processes.

What Ingredients Are Used in Lambics?

Lambics are fermented and aged with a unique process, but they also use ingredients that set them apart from other beers. They are brewed with a base that is about two-thirds malted barley and one-third unmalted wheat.

Large quantities of hops are used to brew this beer, but not for bitterness. Because the fermentation and aging process is especially long for Lambics the preservative qualities of hops are very desirable. However, the distinctive flavor of the beer would not be well-served by hop bitterness. To get the protective qualities of the hops without over-bittering the beer, aged hops are used. These hops have lost much of their bitterness but still provide protection from infection by wild bacteria.

Using aged hops also changes the aroma of the beer. Instead of the citrus or herbal odors that are generally associated with hoppy beer, the aroma from aged hops is described as “cheese-like.”

Using Lambics In Blended Beer


Lambic can be enjoyed on its own, but this style is actually more often used as the base in a mixed beer. Sometimes these mixtures are of Lambics of a different age. It is difficult to produce Lambic with a consistent flavor from one year to the next due to the dependence upon the wild bacteria and yeast in the air and in the aging barrels. Mixing older and younger beers can produce a Lambic with a more consistent flavor from year to year. This blend of various Lambics is called “Gueuze.”

Gueuze is actually aged for about a year after it is bottled because the younger Lambics in the mixture are not finished fermenting yet. A secondary fermentation takes place in the bottle during this time. Even after aging for a year in the bottle, Gueuze actually gets even better with more age. It is not uncommon to have Gueuze aged for ten to twenty years and still be good.


Another common blended beer made with Lambic is called Faro. This beer is a blend of young Lambics that is sweetened using a candy sugar. The beer is then pasteurized before being bottled so that further fermentation does not take place in the bottle. This beer has a very sweet character due to the unfermented candy sugar.


There are many variations of Lambic in which whole fruit is added after fermentation to change the flavor. The sugar in the fruit encourages a secondary fermentation. Wild bacteria on the fruit skins add to the character of the beer. Typical fruits used to make this style include cherries, raspberries, peaches, and strawberries.

Do you have a favorite Lambic? What is it?