How to Achieve a Great Beer Fermentation - Rules, Tips and Tricks

(Hey all! Josh here from HBD. A quick heads up - those of you who have attended Home Brew Depot's Beer Brewing Masterclass, this is your next step so you should have your wort in your fermenter and your yeast ready to pitch. Enjoy!)

O.K! So we have our wort ready in our fermenter, and we have our yeast prepped and ready to go. What do you do now to ensure a great fermentation? As with all our posts, I'm going to break it down as simply as possible in step-by-step format and give a short explanation to help you understand some of the key points and important rules. Occasionally, I'll throw in some technical jargon if you feel you want to delve a little deeper.

Let's look at some of the rules, tips, and tricks to make sure you have a great fermentation, every single time.

1. Get your wort to the correct temperature.  

When we brewed our wort we kept in mind that we needed to create the perfect environment for our yeast to take over and start converting the sugars into alcohol and C02. The perfect environment includes the perfect temperature because if our wort is too cold the yeast will remain dormant and won't eat up those tasty sugars and turn our wort into beer. If the temperature is too high, we risk a rapid fermentation and the creation of common 'off flavors' such as fusel alcohols (heavy solvent) and diacetyl (buttery, movie popcorn). 

temperature gauge

Different beers require different fermentation temps.

The Method. The key is to make sure your wort is cooled down to the correct temperature range before pitching (adding) your yeast. For best results, I would also recommend adding your yeast to the lower end of the suggested temp range, as the fermentation itself can generate around 10 ˚F in heat. For example, if brewing an ale, the standard temperature range is usually 68 ˚F (20 ˚C) to an absolute max of 80 ˚F (26.6 ˚C), so I like to aim for 70 ˚F for my wort before pitching my yeast.

Side note: Please be aware that depending on what you're brewing, the fermentation temp can differ wildly. For example, some saison yeasts can be fermented quite happily at 90 ˚F, while some very clean lager strains can go as low as 40 ˚F. If you are just starting out, always consult your recipe or use the yeast instructions as guidelines.

Now I know keeping your wort at 70 ˚F for 1-2 weeks can be a problem, especially if you live in a hot country or it's the height of summer. One simple trick is to wrap your fermenter in a wet towel and point a fan at it. Another is to put your fermenter in a larger vessel full of water and add ice to keep your desired temperature. This water acts as a 'buffer' against the hotter ambient air temperatures and helps regulate the temp of your beer. A lot of people brew in colder seasons to make this easier (and used to be the law in Germany! Research: Reinheitsgebot). You could also fully commit to your new brewing obsession and build a temperature controlled chamber like this one. Or get a fermentation jacket that encases your fermenter. This is sort of like a flexible cool box which you can add ice packs too if needed. 

2. Take a Gravity Reading.

Refractometer OR Hydrometer

You'll need a refractometer or a hydrometer to take a reading.

If you want to know the ABV (alcohol by volume) of your beer, the efficiency of your mash and overall brew day (and you should - you'll need to know these things if you want to improve) you will need to take a gravity reading before and after fermentation. A gravity reading will tell you how many sugars we've managed to extract from our grains, or basically the sugar density compared to the water density of our wort.

The initial reading is called the Original Gravity, or 'OG' for short, and is taken before we ever add our yeast. When we take a reading before and after fermentation, we can compare to see exactly how many sugars the yeast has eaten and replaced with alcohol. Essentially, the Original Gravity will lower as the sugar is replaced with alcohol becoming less dense until the yeast has finished its work. What we're left with is the Finished Gravity or 'FG' for short.

Example: Water has a gravity reading of 1, so our Wort will have an OG higher than this. For most ales, it will probably be between 1.035 and 1.060. You should consult your recipe sheet as the target OG can be worked out by grain type/weight, water used and yeast before brewing has even started so you'll know exactly what your target should be. As fermentation happens, this number will lower until it eventually stops due to yeast inactivity. This is our FG.

(Technical Jargon: The Specific Gravity of a liquid is that liquid’s density compared to water. So a liquid with a Specific Gravity of 1.050 is 1.05 times the density of water. Let's say the OG is 1.050 before fermentation, and once fermentation is finished we are left with an FG of 1.010. To calculate our ABV we can use the following calculation: 

ABV = 132.715(OG-FG)

So basically: 

ABV = 132.715 (1.050-1.010)
ABV = 132.715 (.040)
ABV = 5.31%

If math isn't your thing, don't worry. There are literally hundreds of apps and calculators out there to do it for you. I usually use the free ABV calculator provided by Brewers Friend. )

The Method. You'll need either a hydrometer and testing tube or a refractometer to get your OG and FG readings. Each can be picked up for less than $20 from either your local homebrew store (ALWAYS support your LHBS) or online.

Step 1: Use a sanitized glass to collect a sample of wort. If you have a tap on your fermenter, even better! You'll need around half a cup for your hydrometer, but only a pipette full for a refractometer. Remember that everytime you collect a sample you risk bacteria getting into your beer, so if there is a way to extract some wort without exposure, always take that option.

Step 2: Get the wort sample to 59 ˚F (15 ˚C), or whatever your hydrometer/refractometer is calibrated to. Hydrometers/refractometers are temperature dependent, so you'll need to make sure you're at the right temperature before taking the reading. If you're not at the right temperature, you can always use a gravity reading temperature adjustment chart like this one.

Step 3 (Hydrometer only): Add the wort to your testing tube or sight glass, being careful to not have excess foam. Foam can be a bit of a nightmare getting a reading and can fudge your calculations as it sometimes sticks the hydrometer to the walls of the glass. Once the hydrometer is settled, take a reading where the hydrometer hits the surface of the wort. This is your gravity reading!

Step 3 (Refractometer only): Use a pipette (most refractometers come with one) and take some of your wort sample. Open the sample plate and make sure it is clean and dry. Squirt a few drops of your wort onto it, then close it. Hold the refractometer up to a natural light source and look through the sight tube. If it is blurry, turn the sight tube until it becomes clear. Look where the line (usually blue) hits the OG chart. This is your gravity reading!

Now you have your OG, we will wait until fermentation is finished to get your FG.


3. Get some Oxygen in the wort. 

Before we add our yeast we need to make sure the wort is properly aerated as oxygen is an important part of yeast growth. If we neglect to aerate our wort, this can lead to issues such as an incomplete fermentation, or it never starting in the first place. Lack of oxygen can also lead to the excessive production of esters (or fruity flavors) which can ruin the beer.

(Technical Jargon: Professional Breweries shoot for  8-10ppm (parts per million) dissolved oxygen in beer. If we use good old-fashioned air, which is around 21% oxygen, we can dissolve 8ppm, so that's exactly what we're going to do!)

The method. Listen, you don't need to over complicate this. Your fermenter should have some 'headspace' at the top, which contains the oxygen you need to aerate your wort. Make sure your fermenter is sealed and then either rock it back and forth for a minute or give it a light shake. Please do be careful - you're not conducting a mafia shakedown or Bez from Happy Mondays - the last thing you want is your sticky wort going everywhere. Nightmare. Some people will sanitize electric whisks or spoons but in my opinion, the fewer things going into the fermenter that could potentially expose it to unwanted beasties and bacteria, the better. It's worth pointing out that technically, the most effective aeration would be to inject pure oxygen into your beers, but let's not start buying expensive O2 injection kits until we have a problem worth fixing. Shaking and sloshing will usually see you right.


4. Sanitise your airlock, yeast vessel... and hands. 

Yep, you read that right. Now some people might find this overkill, but I never like to take any chances. I always have a spray bottle with some non-rinse sanitizer (the industry standard is Starsan) available as a few squirts can do the trick. I spray the yeast packet, my bung/cap for the top of the fermenter, the airlock and if needed, my yeast vessel. The reason for such intense levels of sanitization is that the last thing you want is to get bacteria into your beer at such a crucial stage.

Starsan spray

A starsan spray bottle makes life easy!


Remember: Proper sanitization and good fermentation temperatures are key to a good fermentation! Never forget this, and you're already well on your way to great beer!

5. Keep it out of Sunlight. 

Vampire burning in sunlight

Much like vampires, beer does not fair well in sunlight.

The hops found in the beer react to direct sunlight, sometimes in as little as 30 seconds and can create an unpleasant sulfury 'skunked' flavor. If you've ever had a skunked beer, you'll know just what I'm talking about. It's gross. This goes for finished beer, too. There is a reason good beer is sold in brown glass bottles, as this color glass allows less blue, green and UV light through to damage the beer. Clear bottles allow no protection, blue bottles let blue light through, and green bottles allow green light. You've probably noticed that more and more breweries are adopting canning lines. This is almost certainly in part because it increases shelf-life and removes any chance of the beer becoming 'skunked' or 'lightstruck'. 

The Method. There isn't a lot more to explain here, really. Keep your fermenter in a dark place out of direct sunlight! 

(Technical Jargon: When light hits our beer, it can create a photochemical reaction that transforms the iso-alpha-acids from our hops into 3-methyl-2-butene-1-thiol. The “thiol” part of this tongue twister refers to the sulfur compounds, which are what create that unpleasant aroma and taste. Funnily enough, it is this same compound actual skunks produce in self-defense, which is likely where the reaction got its moniker.)

6. Add your Yeast!

Woohoo! It's that magic hour! Whether it is a yeast starter or a packet of dried, now is the time to add your yeast.

add dried yeast

Adding Dried Yeast. The other method is making a yeast starter.

The Method. Making sure everything is sanitized, carefully take off the cap/bung of your airlock and pour your yeast into the top of the fermenter. Take your airlock and fill it halfway with sanitizer solution and fit it back into the cap/bung, then back into the fermenter. It's important to do it this way as if you try and push your airlock into the cap/bung when it is already in the fermenter, the pressure it is going to shoot sanitizer solution out the top of your airlock. Attach it carefully! Also worth saying - If you are using a bubbler airlock, make sure to fill both sides halfway. For higher gravity beers (I usually set the bar at 1.060) I'll always use a blowoff tube, which is essentially a piece of sanitized tube that runs all the way from the cap/bung to a glass or jug of sanitized water and is fastened securely in place. This is because a vigorous fermentation can work its way up through a regular airlock rendering it useless, so a blowoff tube negates any issues.

Then Voila! You've just started your fermentation! Congratulations. Now it is time to let the yeast take over and do its thing. This would be the perfect time to celebrate with a previous homebrew or a nice cold craft beer. You deserve it!


7. How do I know when fermentation is complete?

The short answer: Wait at least 5 days, or until you see no activity from your airlock or in your fermenter. As before, take a gravity reading with your hydrometer or refractometer. Mark down the result. Wait 24 hours and take another reading. If the reading is the same, primary fermentation is complete! If it has lowered, primary fermentation is still happening. Repeat every 24 hours until you have a steady reading. 

(REMEMBER: Every time you take a reading you expose your beer to contaminates! This method works best when your fermenter has a tap, so no contaminants get into your beer. If you don't have a tap on your fermenter, I advise reading the long answer.)

The long answer: When brewing an ale, the first fermentation, or primary fermentation, should be done in less than a week (if you've followed all the above rules and steps correctly). Primary fermentation can actually complete in 48-72 hours, but sometimes it will need for a full 1-2 weeks to make sure all primary activity has completed. If you have a well-sealed fermenter, you'll see no airlock bubbling activity, or if your fermenter is clear you'll see no activity in the fermenter, your yeast will have formed a sediment at the bottom of the fermenter and the krausen (the rocky, foaming head) will have subsided somewhat.

Once you're at this point where primary fermentation has finished, you're now into the 'conditioning' phase, which is where the yeast begins to eat some of the heavier sugars and clean up some of its own by-products created during primary fermentation. This is paramount for good clean beer and removing some unwanted off flavors. 

You can either leave the beer for another 2-3 weeks in the primary fermenter to allow for this conditioning to take place or transfer your beer to a secondary fermenter. Some people prefer transferring to a secondary vessel for conditioning (myself included) as if the beer is sat on the inactive yeast sediment, coagulated proteins and fats at the bottom of the fermenter (also know as the 'trub'), the trub can actually start to impart soapy flavors and other unwanted off flavors into our beer. When left dormant on the beer too long, the now inactive yeast can also go through 'autolysis',  a form of self-destruction, which can impart meaty, fatty flavors to our beer. As you can imagine, this is also gross. So the goal of the secondary fermenter is to remove any chance of this happening and to allow for a nice, clean conditioning phase.

(NOTE: Once conditioning is over, you'll need to take another gravity reading as detailed before. This will be your FG and with it, you can work out what your ABV is! Exciting times!)

Pros and Cons. As a beginner, leaving your beer in the primary fermenter for a couple of weeks extra to go through 'secondary fermentation' is sometimes advised by the homebrewing world as any time you transfer your beer from one vessel to another you risk contamination. However, I believe the risk of the above-mentioned factors outweighs this argument and that if you are diligent with your sanitization routine you will be absolutely fine. Brewing requires a nearly OCD level of cleanliness, and I always advise this be the first thing you learn. It might not be the most fun part of brewing, but it will save you time, money and disappointment! There will also be times where you're going to want to add extra additions to your beer - such as more hops, cocoa nibs, coffee etc - and this requires you to open your fermenter anyway. If adding these things, always rack (transfer) your beer to a secondary to make sure the only extra flavors you're imparting are from what you're adding in.


8. You have your beer! What now?

Great job. You now have your beer ready to either bottle or keg, depending on which route you want to go down. If you feel like bottling is your game, you can follow my easy step-by-step bottling guide, designed to be super simple and easy to follow. 

I really do hope you enjoyed this article! You can find more step-by-step guides, helpful articles, and resources on our blog. If you fancy some hands-on experience and find yourself in Southern California, you should check out one of our beer brewing masterclasses! it's a lot of fun in one day and requires no experience.

If you found this post helpful, please share it with anyone you think might benefit from it. Also feel free to comment! I'll answer all comments as best I can. 

Happy brewing!

Joshua James

Brewer / Host / Nerd




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