FERMENTATION - What To Expect

HBO_StaffHBO_Staff Posts: 1,853Administrator
edited February 2016 in Welcome To The Forum

Brews ferment in different ways and at different speeds, there is no hard and fast rule of what to expect. Once a brew has been mixed up and the yeast added, a brew will then start it's fermentation. In some cases you will see vigorous action, foam and froth, bubbles, the airlock or even the lid may need removing to allow for it, other times there will be very little to see and the airlock will never bubble. In the case of a vigorous ferment this will usually last for only a day or two, then it will calm right down and just slowly finish fermenting, or in the case of a much calmer ferment it may take longer, but it will get there. 

You may or may not have bubbles rising though your airlock if using one, and the lid of the bucket may dome upwards with any pressure inside the vessel. An airlock will not always bubble but this is nothing to worry about, sometimes there is not enough pressure to force any gases past the water in the airlock, or there may be the tiniest of holes somewhere, either on the lid or where the airlock is fitted to the lid, and any gas will always escape through the point of least resistance. It does not matter, your brew does not need to be airtight during this initial stage, the main idea is just to keep any contaminants out. Indeed some starter kits do not come with an airlock, they just say to loosely fit the lid to allow any gases to escape, the main idea is that gas can escape to avoid any excess pressure in the vessel.

The speed and amount of action you will see from a fermentation depends on many factors, including the brew itself, the yeast used, temperature, etc. As a general guide warmer temperatures produce a more vigorous ferment, and cooler temperatures a slower fermentation, with some brews slower fermentations can improve the end result, but also test your patience!

It is common for the sediment to settle to the bottom of the vessel and cause a layer of debris, this can be in the form of a 'sludge' or thick layer, and sometimes you will get froth, or a 'scum' like appearance on the surface with bits in it, this is all part of the fermentation process and is nothing to worry about.

There is only one true way to know how your fermentation is doing - use a hydrometer to take readings. Ideally take a reading at the start once the brew is mixed then you have a number to compare progress to, then after a few days you can take another reading and monitor how it is doing, the reading will steadily get lower on the scale as it nears completion. It is not uncommon for people to think their brew is not fermenting, but when checked with a hydrometer the reading shows the brew has actually finished, so always check to be sure.

If a brew stops and you believe you have a 'stuck' fermentation, in the first instance giving it a stir will often get it going again, and making sure the temperature is nice and warm will give the yeast it's best chance. 'Re-start' yeast is available if needed, but try stirring it first and check the reading a day or so later.

You know you are ready to either move on to the next stage or transfer your brew to a keg (barrel) or bottles when the reading is nice and low, some manufacturers give a reading on your hydrometer to aim for, and also when all signs of any small bubbles rising through the liquid to the surface have stopped completely (bubbles and froth may still be on the surface). The reading should then be checked again after 24 hours to be sure that it hasn't changed and is exactly the same. No bubbles rising and a constant low reading show it is ready for moving on to the next stage. If not sure, wait an extra day or so and check again, this is particularly important if transferring your brew to bottles as bottling too early means there could be gas still being produced, and in a bottle this excess pressure has nowhere to escape, at least in a barrel there is a safety vent for releasing any excess pressure if needed. The idea is simple;

- Try and maintain a nice warm temperature (as recommended by the manufacturers if applicable) - often around 20 to 24 degrees C
- Take an initial hydrometer reading. After the yeast is added cover the vessel and leave it to get on with it
- Take a reading after a couple of days to check on it's progress if needed, otherwise wait for any bubbles to stop rising
- Check with your hydrometer that the reading is nice and low, then compare it to a second reading 24 hours later
- Once you are sure it is finished, move on to the next stage, if not sure, give it another day or so

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