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Fermentation FAQ

Fermentation Questions

My beer kit needs sugar, what type of sugar should I use?

Most single-can beer kits require about 1kg of sugar to be added, although some may need as much as 1.5kg. You can use almost any type of sugar, even table sugar, however, this will affect both the taste of your finished beer and what’s known as mouth-feel i.e. your beer will feel “thinner” and have less body. You can use dedicated brewing sugar, but for best results use beer kit enhancer or malt extract as a weight-for-weight replacement. Yeast will convert less of the malt to alcohol, than standard sugar, which will give youe beer a desirable sweetness and more body.

My wine or cider kit needs sugar, what type of sugar should I use?

Although most wine kits don't need extra sugar, there are a few that do and most single-can cider kits will also need about 1kg of sugar. You can use castor sugar, or brewing sugar. Yeast find brewing sugar easier to metabolise, so fermentation will start more quickly and generally be more vigorous. 

What is malt extract?

Malt is a type of sugar (maltose), produced by germinating grain (usually barley), which has then been roasted. The sugar is then washed out of the grain and either concentrated in liquid form (LME – Liquid Malt Extract), or spray-dried into a powder (DME – Dried Malt Extract also called Spray Malt). Malt Extract comes in a variety of types, depending on the grain used and how much roasting the grains have undergone, such as extra light, light, medium, dark and extra dark. Liquid malt extract usually comes in 1.5kg tins, but can also be purchased in 25 litre jerry cans and in both hopped and un-hopped varieties.

What is Brew Enhancer / Beer Kit Enhancer?

Beer Kit enhancer (BKE) or Brew Enhancer is a mixture of brewing sugar (dextrose) and malt extract. Using a brew enhancer will give your beer more body and flavour than just using sugar, and will also give your beer a better head, when poured.

What other types of sugar can I use?

You can use almost any type of sugar in your beer, including honey, but what you use will affect the flavour. Treacle is a popular addition to stouts as it helps to add a distinctive coffee bitterness, while Golden Syrup is often added to lighter beers and ales. Honey should be used carefully as it can overwhelm the taste of your beer, but used in moderation can add an interesting flavour. Many home brewers like to use Belgian candy sugar for bottling. Many sugar syrups, such as treacle, Golden Syrup and molasses, contain some water, however, so are not 100% fermentable (more like 75-80%), so if using on a weight-for-weight basis, will require an extra 20% or so to be added.

How long should I leave my beer in the fermentation vessel?

Most beer kits will tell you that your beer will finish fermenting after three to four days; however, while some beers will ferment this quickly, many will take longer. Ideally, you should leave the beer in the fermentation vessel for at least 10 days, and preferably two weeks. This will not only ensure that the fermentation process has completed, it will enable the yeast to clear up, removing any off flavours. The longer you leave it, the more yeast will sink to the bottom of the fermentation vessel, too, resulting in a clearer beer.

Beer can often be left for three weeks or so in the original fermentation container, but if you plan on leaving it longer, then it would be wise to syphon the beer off the dead yeast, into a clean, sterilised, secondary fermentation vessel.

How long should I leave my wine or cider in the fermentation vessel?

This depends on the kit you are making. Some wine kits will ferment out in as little as four days, most others and ciders will take a little longer. Country wines and home-made cider can take as long as 3 weeks to ferment. The only sure way to tell if fermentaiton has finished is to take a hydometer reading. (See the guides section on how to use a hydrometer).

What temperature do I need to ferment at?

Most beers and some lagers will use an ale yeast. The ideal temperature range for these would be between 18 to 20°C, which is fortunately the temperature which most houses with central heating are kept at! Yeast will produce heat in the first day or two of vigorous fermentation, enough to raise the liquid temperature by two to three degrees, so it’s important that the starting temperature is no higher than 20°C.

If you are making lager with a proper lager yeast, then the fermentation needs to be cooler, at around seven to 13°C, depending on the yeast variety. This is a lot colder than most houses, so you may need to ferment your lager in an out-building during the colder months, or convert an old fridge into a fermentation fridge with a dedicated temperature controller (see the guides pages for more info).

Wine and Cider are also temperature dependent. The ideal fermentation temperature is 20°C, but anywhere between 18-22°C is suitable.

What if the fermentation temperature is too cold?

Yeasts work best at certain temperatures and if it’s too cold they become less efficient, leading to much longer fermentation times. For example, a yeast that will ferment out in a week at 18 to 20°C will take two to three weeks at 16°C. If the temperature drops too far below the ideal range, then the yeast can become dormant and fermentation will stop completely, although once the temperature is raised, the yeast will wake back up and fermentation will start again.

If your fermentation area is too cold, you can increase the temperature of the fermenting beer in several ways:

  • Use a brew belt – a heated belt which fits around the fermentation vessel. Best used with a thermostat or digital temperature controller
  • Heat pad – this is an electrically-powered mat which sits under the fermentation vessel and provides a source of heat
  • Water bath – By placing the fermentation vessel inside a water-filled bucket or tank, the water temperature can raised with an aquarium heater
  • Submersible heater – A sterilised aquarium heater can be immersed into the fermenting beer. This carries a risk of introducing an infection to your brew, so the water bath method is preferred
  • Fermentation fridge – A fridge which uses a digital temperature controller to control both a heater and/or the fridge compressor, to maintain a pre-programmed temperature


What if the fermentation temperature is too hot?

Too high a fermentation temperature can be quite detrimental to your brew, resulting in the development of “off flavours” (generally banana/fruity in beer), as well as the production of fusel alcohols. Fusel alcohols can not only give your brew an unpleasant, sharp alcohol taste but are also thought to contribute to hangovers! To cool your fermenting brew and keep it between 18-20°C, you can try the following methods:

  • Water bath – Place the fermentation vessel inside a water-filled bucket or tank, and then drape towels over the edge of the water bath, with one end in the water. The water will evaporate from the towels, cooling the water bath and your brew.
  • Wet towel wrap – Wrapping wet towels will help to cool your brew as the water evaporates, but the towels will need re-wetting at regular intervals.
  • Fermentation fridge – A fridge which uses a digital temperature controller to control both a heater and the fridge compressor, to maintain a pre-programmed temperature.


Should I rehydrate my yeast?

This depends on your yeast. Young’s, which supplies many yeasts, says that during the manufacturing process of their yeasts, special processes are used to promote high levels of a compound call Trehalose within the yeast cells. These high levels of Trehalose help to protect the yeast in storage, as well as recover quickly when added to wine must or beer wort and that therefore, rehydration is not neccessary. However, some yeast manufactures specifically instruct you to rehydrate their yeasts, by adding to a small amount of water between 35 to 40°C, covering and leaving to rest for 15 mins to half an hour. Check the yeast packet for any rehydration instructions, before pitching.

Do I need an airlock on my fermentation vessel?

Fitting an airlock to your fermentation vessel’s lid isn’t absolutely necessary, but it will help to keep dirt, bacteria and other air-borne nasties, out of your brew. Because yeast produces CO2 during the fermentation process, this will rise to the surface of your brew and provide a protective layer, which stops your beer, wine or cider from oxidising and spoiling, but it won’t of course stop things falling into your brew. If you don’t have an airlock, you can leave the lid of the fermentation vessel open slightly, to allow the excess CO2 to escape. However, for the sake of a few pounds, we’d suggest using an airlock, which not only helps keep your brew free from bugs, it can give you an indication of how the fermentation process is progressing.

Why isn’t my airlock bubbling?

There may be several reasons for this. It may be that fermentation hasn’t yet started, or if it was bubbling and is no longer doing so, then the most vigorous part of the fermentation process may be over. In many cases, it is because the lids on fermentation vessels don’t always form a perfect seal and so the CO2 gas is able to escape from somewhere else. This is particularly true if the airlock has a lot of liquid in it, which forces the gas to escape from an area of lower resistance. Just because an airlock has stopped bubbling though, does not mean fermentation has finished: using a hydrometer is the only way to reliably establish if the fermentation process has completed, or if it is still progressing.

What is the froth on top of my beer?

This is a foam (known as Kräusen) casued by the creation of large volumnes of CO2 by the yeast. It usually appears about a day after the yeast has been added, and dissipates again a day or two later and is a perfectly normal part of the fermentation process. Once the Kräusen subsides, the side of the fermentation vessel will be covered in a brown, sticky residue. This is very bitter and it is important that it is not stirred back into your beer. Some fermentation vessels have a removable sleeve, called a Kräusen collar, which can be removed once the foam has dissipated, but there is no real advantage to it.

How do I know when fermentation has finished?

The only sure way to tell if fermentation has finished is to use a hydrometer reading. A sample of beer is placed into a trial jar and the hydrometer is placed into the liquid. If the same reading is taken for three days, then fermentation has stopped. Typically this reading will be around 1.012, but may be as high as 1.014 or as low as 1.008. If the reading is higher than 1.014 for each reading, then fermentation may have stuck and depending on the reading, may need restarting.

Airlock activity should not be relied on to measure fermentation progress, as the released CO2 may be able to escape from the fermentation vessel, via another route.

What is a stuck Fermentation / how can I restart a stuck fermentation?

A stuck fermentation is when the yeast stops producing alcohol, before it has used all the available sugar. This can be caused by a lack of aeration before the yeast was pitched, a drop in temperature, using out-of-date yeast and other reasons. A stuck fermentation can be detected when a high gravity reading, for example 1.020, is taken after the period in which fermentation should have completed, say two weeks.

To restart a stuck fermentation, first ensure that the brew is at the correct temperature and if not, take steps to increase it. If cold is not a factor, then add some yeast nutrient to the brew and give the liquid a gentle stir with a sanitised spoon or beer paddle, taking care not to splash the liquid. If this doesn’t work, then you can try adding more yeast or a special restart yeast.

It's very important that your brew completely ferments out , otherwise if you bottle the beer, wine or cider and it starts to ferment again, the excess sugar could cause the yeast to produce so much CO2 that the bottles explode.

What is dry hopping?

Dry hopping is the technique of adding hops to a beer after fermentation has finished and before it is bottled. It can be used with any beer but is often used with kit beers to add extra flavour, or to “tweak” the beer. Dry hopping adds hop aroma, but not bitterness.

To dry hop a beer, a small amount of hops (typically 20-30g) are placed, along with a sterilised weight into a sterilised muslin bag or hop sock. The hop bag is then suspended in the beer for a maximum of five days (any longer and the beer can develop unwanted, grassy flavours). Dry hopping is best done immediately before bottling to preserve the hop aroma.

If you don’t have a muslin bag or hop sock, then you can add loose hops to the beer, however, these will need to be strained before bottling.

What is a hop tea?

This is where hops are added to water at 80°C and then allowed to steep in this hot water for around 30 minutes. This process is mainly used with kit beers to add extra flavour and aroma. Once the hops have stepped for the required time, the hops are strained out of the liquid and the resulting “tea” is added to the wort, before the yeast is added (pitched). Alternatively you can make a hop tea and add it to the fermenting wort, after the main fermentation has finished, a week or so before botttling.

What’s the yellow/red slime at the bottom of my fermentation vessel?

This is the dead yeast which falls to the bottom of the fermentation vessel, once it has done its job of turning the sugars in the liquid to beer, wine or cider. It’s referred to as the yeast cake, lees or trub. While it may not look very pleasant, it’s a perfectly natural by-product of the fermentation process and can be safely disposed of down the drain or even used as a plant food in your garden!

How do I make my beer stronger

There are two ways of doing this, either adding more fermentable material (i.e. sugar, malt extract, etc.) or by reducing the volume of water added. Many kit beers make 40 pints, or 23 litres of beer. A common technique used by many home brewers is to “shorten” the brew, by only adding enough water to make 21 litres of beer. Adding more sugar will increase the alcohol content of your beer, but it will also make the beer taste more watery (reduced mouth-feel) and lacking in body. This is because beer’s flavour comes from three main sources; the malt, the hops and the yeast. If you want to increase the strength without reducing the volume, then it’s best to use malt extract (either dried or liquid) or at the very least, beer enhancer, which is half and half, sugar and malt extract.

If you want a really strong beer, you can both increase the malt content and reduce the volume, however, if you do this with a kit beer, you will significantly change the flavour characteristics.

How do I make my beer weaker?

If you prefer more of a session beer, you can reduce the alcohol content in two ways; by using less fermentables (e.g. sugar, malt extract, etc.), or by adding more water (lengthen the brew). When used with kit beers, either technique should be used with caution, as they can make the finished beer taste watery, lack body, have poor head retention and reduce mouth-feel.

If brewing extract or All Grain recipes, then look for a recipe which will produce a lower ABV beer, without affecting the taste and body.