Fermentation

Getting the fermentation right is as important in making a good beer as using good ingredients and ensuring good sanitation. Fortunately, a little time and effort can ensure a good fermentation.

 

 

Fermentation

Getting the fermentation right is one of the keys to making good homebrew. Among other things, there needs to be enough oxygen in the wort for the yeast to multiply and the temperature needs to be correct so that the yeast doesn't stop working if it gets too cold or produce off flavours if it's too warm. Fortunately, a little time and effort can ensure a good fermentation.

Whirlpooling

If you're an all-grain or partial mash brewer there will be a large amount of coagulated proteins and hops in the wort that you need to remove before transferring to the fermenter or cooling cube. "Whirlpooling" is a process that helps separate out the trub and hops. Malt extract and kit brewers can use the same method to separate hops.

Whirlpooling is as simple as gently stirring the wort in the boiler or saucepan in a circular motion to create a whirlpool. Then put the lid on the vessel and leave it for 10 or 15 minutes. The whirlpool will cause the trub and hops to be concentrated on the bottom and in the centre of the vessel, allowing the wort to be tipped, drawn or siphoned off.

Cooling the wort

Yeast can't be pitched when the wort is too hot. At worst the yeast will be killed and at best it will produce off flavours during fermentation or foam out of the fermenter, or both. The temperature of the wort needs to be below about 25 degrees and ideally close to 20C for most ales when you pitch the yeast. Lager yeast should be pitched cooler then have the temperature reduced to fermentation temperature.

Kit and malt extract brewers

Kit brewers generally don't need to worry about cooling the wort because only a small amount of hot water is used to dissolve the ingredients, steep grain or boil hops. Topping up the fermenter with cold water usually cools the wort to a temperature at which the yeast can be pitched.

However, in partial mash or malt extract beers where the quantity of boiling liquid is greater, or in warm conditions, the temperature of tap water may not bring the wort down enough. This calls for the liquid to be cooled before adding it to the fermenter. The easiest way is to put the hot liquid in a saucepan then place it in a sink of cold water, stirring the liquid with a sanitised spoon every five minutes or so and changing the cold water if it becomes too warm. This will cool the liquid enough so that the wort temperature will be about right when the fermenter is topped up with cold water. When you add the cooled wort to the fermenter, try and leave behind any solids trub may have settled at the bottom of the saucepan.

Other brewers freeze plastic bottles with ice and put them in the fermenter to cool the wort. If you do this, make sure that you sanitise the bottles when you drop them into the fermenter, paying particular attention to nooks and crannies around the lid.

All-grain brewers

All-grain brewers have two option to get wort to pitching temperature: force chillng the wort or using the so-called "no-chill" method.

Chill

If you decide to chill your wort, getting it to pitching temperature as quickly as possible is critical so that wild microbes that would love to settle in your wort and take hold don't get a chance before the yeast is pitched. Another benefit is that rapid chilling helps precipitate out proteins and hop particles from the the wort, which can be left behind when the wort is transferred to the fermenter.

There are several types of wort chillers available to homebrewers.

An immersion chiller is a coil of several metres of copper or stainless steel tube that is submerged in the wort a few minutes before the end of the boil to sanitise it. When the heat is turned off cold water is run through the coil, which cools the wort. The wort will eventually be lowered to a yeast-pitching temperature and can be transferred to the fermenter. Whirlpooling, or stirring the wort when the water is turned on then leaving it, thus causing the wort to pass across the cold-water pipe, increases the efficiency of an immersion heater. The downside of immersion chillers is that they use more water than other chillers. This may not be concern if you run the water into a washing machine or have a rainwater tank from which you can draw the water and to which you can return it. A big advantage of immersion chillers is that they are easier to clean because wort is only ever exposed to the outside surfaces.

In a plate chiller, the hot wort is run between plates through which cold water is running in the opposite direction. If the rate of wort flow is correct, the cooled wort that runs into the fermenter will be at pitching temperature. A plate chiller is a little like a radiator in a car. Plate chillers are quite efficient in the amount of water they use. A disadvantage is that because wort travels through them, care must be taken to be meticulous with cleaning so no wort is left inside that mold can grow on and ruin future brews. See the tutorial on three-vessel brewing for pictures of a plate chiller in action.

A counterflow chiller works on a similar principle to a plate chiller. However, the wort is run through a tube which is inside a larger tube through which cold water is run in the opposite direction.

No-chill

This method involves transferring the hot wort to a sanitised plastic container, squeezing as much air out as possible and sealing it, then allowing it to cool naturally. Wort can be stored for months in the container because it sterile. When the time comes to ferment the wort, it is transferred to the fermenter and aerated, and the wort is pitched.

Ideally, the container - often referred to as a cube, regardless of its shape - will have as little head space as possible when full. Squeeze the container before sealing it so that the the liquid is as close to the top as possible. It's usually the case that containers hold more hot wort than their claimed capacity. For example, most 20-litre containers should hold 23 litres of wort. Any air-tight, food-grade plastic container is suitable.

When using the no-chill method, adjustments have to be made to the hop additions to account for the fact that bitterness will continue to be extracted as the wort cools, unlike if you were force-chilling the wort. A common approach is to reduce all additions by 20 minutes. For example, a 60-minute addition would be added at 40 minutes, a 20-minute addition would be put into the cube and a 0 minute (flamout) addition would become a dry hop addition, or added with a French press.

To see an example of wort in a cube, see the brew-in-a-bag tutorial.

Aeration

In the phase immediately after being added to the sweet wort, yeast needs to multiply to ensure a good fermentation. To do this effectively it needs oxygen.

A lack of oxygen is not such a problem for kit or malt-extract brewers because they don't boil the full volume of wort, although aeration can still be beneficial. Tap water contains oxygen and the action of topping up the fermenter with water mixes oxygen into the wort. So don't be afraid to fill the fermenter vigorously.

For all-grain brewers aeration is particularly important because boiling the wort drives off the oxygen from the wort. There are several ways to ensure there's adequate oxygen in the wort for the yeast to multiply, before it turns its attention to making alcohol and carbon dioxide.

The simplest and cheapest way is to stir the wort vigorously with a long spoon or mash paddle for a few minutes, or until your arm feels like it's about to drop off.

For a mechanised version of this, some brewers attach a paint stirrer to an electric drill and give it a blast for a few minutes. This is an easy and effective method of aeration if you already have a drill. Paint stirrers to fit a drill can be bought cheaply from hardware stores.

Many brewers use an "air stone" to aerate their wort. An air stone is a tube of stainless steel with minute holes in it through which air from an aquarium pump — filtered through a HEPA filter — or pure oxygen is pumped. The holes are usually 2 micron, for use with an air pump or compressed oxygen, or 0.5 micron, for use only with compressed oxygen. The pressure generated by an air pump is not sufficient to get through the 0.5-micron air stones effectively. If you have access to an oxygen bottle from an oxy-acetylene welding kit you can use this.

Airlock or not?

Fermenters come with a lid and a small hole to fit an airlock, which is filled with water and allows CO2 created by the yeast during fermentation to escape, but does not let any outside air into the fermenter.

While there's nothing wrong with using a lid and air lock, many brewers have begun fitting plastic food wrap over the fermenter so they don't have to worry about sanitising the lid and because they can see the fermentation more clearly. If you decide to use plastic wrap, remove the rubber seal from inside the lid and use it to secure the food wrap to the neck of the fermenter. There's no need to put any holes in the wrap; the CO2 will find its own way out.

Measuring specific gravity & calculating alchol content

Most homebrewers want to know the alcohol content of their beer, and taking specific gravity readings is the key to being able to work it out. Specific gravity measures the density of liquid. As yeast converts sugars in the wort to alcohol and carbon dioxide, the wort becomes less dense and the specific gravity drops. By comparing the specific gravity before fermentation (known as original gravity, or OG) to that after fermentation (final gravity, or FG) and applying a formula it's possible to fairly accurately work out the alcohol content.

Taking gravity readings is the only sure way to know that a beer has stopped fermenting. The same gravity reading on three consecutive days — or two identical readings three days apart — indicates that fermentation has finished, provided the beer is about the expected final gravity. (A higher-than-expected gravity could indicate that the beer has not fully fermented, perhaps due to the temperature dropping too low for the yeast to work or fermentation becoming "stuck".)

Measuring specific gravity also becomes important if you start doing all-grain brews because it allows you to work out the efficiency of your mash and whether you need to add water to achieve a particular gravity before pitching the yeast.

On the other hand, many brewers make perfectly good beer without ever taking a specific gravity reading, but for them the ever-present risk is that they will bottle a beer that hasn't finished fermenting, and end up with "bottle bombs" caused by the beer continuing to ferment in the bottles and exploding due to the pressure.

The most common method of taking an SG reading is using a hydrometer, which comes with most brewing kits. A hydrometer is a glass tube that is floated in a sample of the wort or beer so that a reading can be taken from the increments on its side. Pure water at the temperature for which the hydrometer is calibrated (usually 20C) will give a reading of 1.000. Wort before fermentation will have a higher reading because it is more dense due to the sugars dissolved in the liquid. For instance, a "kit and kilo" brew in 23 litres should have a gravity before fermentation about 1.045. This reading will drop about 75 per cent during fermentation depending on the ingredients and yeast used, so an expected final gravity would be about 1.011.

Specific gravity of the wort before fermentation has begun can also be taken with a piece of equipment called a refractometer. A refractometer is a particularly useful tool for all-grain brewers because they often want to take SG readings at various stages during the mash and boil, and only a drop or two of wort is needed to take a reading. In contrast, a hydrometer requires several hundred millilitres of wort, which must be cooled before a reading can be taken.

Step by step: Taking gravity readings with a hydrometer

Some brewers measure the gravity by putting the hydrometer directly into the wort. Only do this if you want to run the risk of ending up with an undrinkable beer due to an infection introduced by putting the hydrometer into the wort or fermenting beer.

1. Take the first SG reading immediately after you have pitched the yeast and mixed the wort well.
2. Slowly turn on the tap and fill the test vessel that comes with the hydrometer to about three centimetres from the top (there needs to be enough liquid for the hydrometer to float). If you're using a lid and air lock, the air lock will bubble as air is sucked into the fermenter. Don't worry about this.
3. Carefully place the hydrometer into the test tube. Don't drop it in because it may hit the bottom of the test tube and smash.
4. Spin the hydrometer. This is important to remove bubbles that may be on the surface of the hydrometer and cause it to float higher than it should, resulting in a reading higher than it should be.
5. To take an accurate reading you need to be level with the surface of the liquid, so bend down and look at the reading. Most hydrometers are designed for readings to be taken level with the surface of the liquid, not the meniscus that will be clinging slightly to the side of the glass. If in doubt, check the instructions that came with the hydrometer.
6. This reading is the original gravity, or OG. Write it down.
7. Don't tip this liquid back into the fermenter. Pour it down the drain or let it ferment (see below).
8. Leave the wort to ferment.
9. When you think fermentation has finished, draw off 100ml or so of beer through the tap. Tip this liquid down down the sink because it's full of yeast and other sediment that will give a false SG.
10. Fill the hydrometer tube and take a reading as above.
11. Take a reading on the following two days, or another reading in two days. If reading has remained unchanged over this period and it's about the expected gravity, you're ready to bottle.
12. If it has changed wait another day or two before testing again. If it has changed DO NOT BOTTLE because it indicates that fermentation has not finished and you risk bottles exploding.

TIP: After taking a gravity reading, don't pour the wort back into the fermenter because it may have become contaminated. For the sample used to take the original gravity reading, pour it into a glass, cover it with plastic lunch wrap and leave it to ferment. Smell and taste it every couple of days as the sweet liquid turns into beer during the course of fermentation. Likewise, don't be afraid to have a taste of specific gravity readings taken during fermentation.

Step by step: Calculating alcohol content

If you have brewing software it will calculate the alchol content for you when you enter the original and final gravity.

However, you can also work it out using this simple formula:

( ^OG-FG⁄_7.46) + 0.5

Where:

• OG= Original gravity (your initial reading)
• FG = Final gravity (the reading at the end of fermentation).
• The 0.5 is an allowance for the alcohol created during secondary fermentation. If you force carbonate in a keg omit the extra 0.5.

When applying the formula, remove the decimal points from OG & FG (so 1.042 becomes 1042).

For example, let's say the original gravity was 1.045 and final gravity was 1.010, the formula would be:

( ^1045-1010⁄_7.46) + 0.5, which equals ( ³⁵⁄_7.46) + 0.5, which is 4.69 + 0.5.

Therefore, the estimated alcohol by volume (rounded) is 5.2 per cent.

Controlling fermentation temperature

The ideal temperature for fermenting ales is about 18ºC to 20ºC (64ºF to 68ºF). If using a true lager yeast, a temperature of about 7ºC to 12ºC (45ºF to 55ºF) will produce a clean, crisp taste. There is no point using a lager yeast at higher temperatures because off flavours will be produced. Use an ale yeast instead unless you are trying to produce a particular style of beer such as steam beer (California common), which are brewed with lager yeast at ale temperature. If you are a kit brewer, remember that most "lager" kits actually come with an ale yeast, which will stop working at low temperatures. If you are unsure, assume it is an ale yeast and brew it at ale temperature or spend a couple of dollars on a lager yeast and ferment the beer cool.

As well as the right fermentation range, a constant temperature is also important for the yeast to do its work as effectively as possible. Putting the fermenter in an enclosed space such as a cupboard can help reduce temperature fluctuations.

If you time your brewing well - lagers in the cool winter months and ales in the slightly warmer spring and autumn - it will make temperature control far easier and mean you may be able to get away without any artificial temperature control.

Cooling

Many brewers invest in a "fermentation fridge" to ensure a correct and constant temerature during fermentation. Even on their warmest setting refrigerators are likely to be too cold even for lager brewing. You will need to hook up a temperature controller such as an STC-1000 to turn the fridge on and off to maintain a constant temperature. Some temperature controllers only turn on the fridge to cool the fermenting beer when the temperature rises to a set level. However, controllers such as the STC 1000 can also be hooked up to a heat pad or belt to warm up the wort in cold weather. Many brewers will say a fermentation fridge is one of the best investments in brewing equipment and contributes to making a quality beer.

Sitting the fermenter in an ice bath is another method of cooling if the ambient temperature is extreme.

Wrapping the fermenter in a wet towel and keeping the towel well soaked is an effective way to reduce the temperature of the wort up to several degrees. The evaporating water will cool the towel and the fermenter. Directing a fan at the fermenter will increase the rate of evaporation from the towel and keep the wort even cooler.

Heating

If the need arises to heat the wort, there are several options. One is with an aquarium immersion heater. Other methods include a belt heater that is wrapped around the fermenter, placing the fermenter on a heating mat or using a “hot box”, which is a wooden box with a light globe in it. Heat belts and mats are available from most homebrew shops.

Racking

Racking is the transfer of the beer from the primary fermenter (the one in which you pitched the yeast) to a secondary fermenter as fermentation is coming to an end. Some people strongly believe that removing the beer from the yeast cake, hop debris and other "impurities" results in a better-tasing beer than a brew that has not been racked. On the other hand, many brewers swear that racking has absolutely no positive impact and don't see any need for it. It's horses for courses. Give it a go and if you believe it is good for your beer, go with it.

Step by step: Racking

The only extra bits of equipment you will need to rack a beer are a second fermenter and a length of food-safe hose. The hose needs to fit on the tap of the primary fermenter and be a little longer than the height of whatever the primary fermenter will be placed on when racking. The reason for this is that when racking the beer needs to run gently into the secondary fermenter with no splashing, so as to avoid admitting oxygen into the beer that at this stage would spoil it.

1. Place the primary fermenter (the one full of beer) on a table or bench.
2. Sanitise the second fermenter and the plastic hose.
3. Place the secondary fermenter on the floor beneath the tap of the primary fermenter.
4. Loosen the lid or cling wrap from the primary fermenter
5. Draw off a little beer from the primary fermenter to clear any trub from the tap.
6. Attach the hose to primary fermenter and put it into the seconary fermenter.
7. Coil any extra hose it in the bottom of the secondary fermenter to ensure the beer is delivered as gently as possible.
8. Make sure the tap on the secondary fermenter is turned off!
9. Turn on the tap on the primary fermenter and adjust it to a steady flow. Avoid letting it run too fast and splashing in the secondary fermenter, which would admit oxygen.
10. If necessary tip the primary fermenter as the level drops so that the tap remains submerged but no trub is drawn into it.
11. When the transfer is complete remove the hose from the secondary fermenter and fit the lid or a piece of plastic food wrap.
12. Put the fermenter somewhere for the remainder of the fermentation.

Note: The same or similar method as racking is employed when transferring a beer to be matured in a fermenter or lagered.

Fining

Finings are added after fermentation to help yeast drop from suspension to the bottom of the fermenter, or "drop bright". Household gelatine can be used for fining, while isinglass, made from the swim bladder of fish, is a traditional fining agent.

In Australia, most homebrewers do not use finings. Fining is most often associated with cask-conditioned ales, so in Britain it is much more popular.

Before adding finings rack the beer from the primary fermenter so that as much yeast as possible is left behind.

Step by step: fining

If using isinglass, follow the instructions on the packet. If there are none, use the procedure below.

1. Confirm fermentation has finished.
2. Mix a 15g sachet of gelatin or finings or soak a leaf of gelatin for 10 minutes in a cup of hot water, covered with plastic food wrap.
3. Remove the leaf of gelatin if using it and discard it.
4. Allow the liquid to cool slightly, covered.
5. Draw off about 500ml (two cups) of beer.
6. Mix the beer with the gelatin liquid.
7. Tip the mixture back into the fermenter.
8. Stir very gently to mix the fining liquid though. Do not be vigorous with the stirring or oxygen will be admitted and risk spoiling the beer.
9. Allow the beer to clear for about a day for the beer to clear then bottle or keg.

Dry hopping

Hops can be added during fermentation. For more information on  in a process called dry hopping or with a technique known as . For details on dry hopping and other methods of hopping in the primary or secondary fermenter (i.e. after racking) see the section on Adding hops and grain.

Diacetyl rest

When brewing beers at low temperatures a chemical called diacetyl is created by the yeast. This can add a flavour usually described as butterscotch to your beer. In most styles of beer this is undesirable, although it is acceptable in low levels in certain beer. So, how is diacetyl production avoided? Well, it can't be. But fortunately it is quite eay to remove the diacetyl from beer. This is done by slowly raising the temperature of the beer as it nears the end of fermentation, in a process called diacetyl rest.

Step by step: Diacetyl rest.