Hello everyone. Jamie McQuillan here, former home brewer and for the past five years owner/operator of Cell Division, my tiny brewery specialising in farmhouse, sour, wild and funky beers. The LoB team decided it would be fun to have me drop in from time to time with an article about various aspects of brewing. This time I’d like to share my experience with bottle conditioning. 

Bottle conditioning in many ways is a rite of passage in the home brewing world. It is a simple, cheap and no fuss process which should end with the pleasure of opening your very own bottle of beautifully carbonated beer. And yet, I hear of many home brewers lamenting that their bottle conditioned beer is either disappointingly flat or in a total fizz and leaping out of the bottle. Either scenario is far from great, especially after all the effort you have gone to get to that point, but the latter is also dangerous, sometimes leading to exploding bottles. 

Maybe you have given up bottle conditioning in favour of kegging/force carbonation, which is admittedly easier, more predictable by nature and certainly the best way to drink hoppy styles at their peak freshness. But bottle conditioning has its place and is something I hope you will agree is worth keeping in your brewing tool box. 

Regardless of the styles you choose to brew, dialling in the correct level of carbonation when bottle conditioning is an art that requires experience and feel, but it is also a science that requires some attention to detail and the understanding of a few basic principles. At times bottle conditioning can be a little unpredictable and awareness of the pitfalls and measures that can be taken to mitigate these are key to your success. Below I will provide some guidelines that I have found to work well for me in my brewery, with some cautionary notes along the way. 

Why bother you say, kegging is much easier

Bottle conditioning is a wonderful and appropriate way of packaging many styles. For example, a Weissbier rolled in the bottle and poured with the yeast just isn’t quite the same when poured on tap. Big, robust strong beers age beautifully when bottle conditioned with care. The live yeast in the bottle also helps to scavenge oxygen which spoils beer, thereby extending shelf life. Many Belgian styles come into their own when packaged traditionally with that thin layer of yeast that remains in the bottle after gifting the beer with lovely natural carbonation. 

Two favourite styles of mine are saisons and sour beers. Saisons are traditionally highly carbonated and really come to life with refermentation in the bottle. In the case of wild and mixed ferment sour beers, the ongoing activity of the yeast and bacteria in the bottle allows for the development of complexity over time. Bottle conditioning really is a must for any self-respecting sour beer brewer!

When is the right time to bottle?

The simple answer is never too soon. One of the most likely causes of over carbonated bottles of beer, other than a nasty infection, is bottling the beer too early. Remember that 2-3 gravity points will be enough to fully carbonate your beer. Thus, bottling your beer 2-3 points short of final gravity will likely see it rocketing all over the ceiling. A good general rule of thumb for a typical clean (Saccharomyces only) beer is to wait at least a week after the primary ferment is over and to ensure you have a stable final gravity over that week. If the gravity is still dropping, wait longer! This not only gives the yeast time to finish cleaning up the beer but also gives the beer time to clear naturally with gravity, at the same time leaving a sufficient amount of suspended yeast to do the job. I recommend you do not rush, adding finings nor cold crash the beer. 

For those of you who are into mixed ferment, wild, sour or funky beers like myself, then a minimum of one month of stable gravity is advisable, but keep in mind your expected `final’ gravity. If it is higher than anticipated, wait it out and remember it only takes a few extra gravity points to turn things into a total disaster. Getting to know your cultures well and how they behave will also give you some level of confidence. 

Priming sugar: selecting your sugar and priming method

Many of us start out bottle conditioning using carbonation drops, adding either 1 or 2 drops directly into each bottle before filling (depending on bottle size and the manufacturer’s instructions). They are fine to begin with but offer very little control over the final level of carbonation. A better method is to use dextrose (corn sugar) which is very fine, dissolves easily and can be added in a measured dose (i.e. 1, 1.5 or 2 tsp) directly to the bottle via a funnel. This is not overly accurate and some small bottle to bottle variation is to be expected, but I will use this method if I have a little extra beer left over after kegging that I want to quickly bottle for home consumption. My preferred method is to bulk prime the beer by dissolving sugar and adding it to the entire batch of beer in a bottling bucket or similar vessel. More on that below. But firstly, you need to calculate how much sugar you need to add. This calculation depends on a number of factors. 

1. Beer Style: The carbonation level you should be aiming for will depend on the style of beer.  For example, the levels range from 1.5-2.0 volumes of CO2 for British Ales through to 3.3-4.5 for German Wheat Beers (try pouring that on draft!). The BJCP guidelines will give you a good feel for whether your beer should have low, medium or high carbonation, particularly if you are entering the beer into competition. However, ultimately some of your choice may come down to personal preference.

2. Residual Level of Carbonation: Residual carbonation is the level of CO2 left in the beer once the ferment is over and this will have a considerable impact on how much additional CO2 is required. You are adding volumes of CO2, so if you think of it like that then it is easy to understand. For example, if the beer is already 1.0 volumes and you want to aim for 2.5 volumes, you only need to add 1.5. But if the beer is very flat, as is often the case for long-aged beers, it may only have 0.3 volumes. This beer will then need an additional 2.2 volumes of CO2 to be adequately carbonated. 

But how do you know how much CO2 is in the beer to begin with? Fortunately, for those of us without tools for testing the CO2 levels, science tells us that for an average home brewed beer fermented at 20oC, there will be approximately 0.86 volumes of CO2 remaining in the beer. This number changes depending on temperature, with warmer ferments retaining less CO2. In my experience, some ferments can also hold onto more or less CO2 depending on the vigour of the ferment and the yeast and/or microbes involved. Residual CO2 in the beer also declines with long-aging. This is where the `art’ to bottle conditioning comes in. Pay attention to the level of fizz in your gravity sample, look at it and taste it. Does it seem to be consistent with what you typically see? If it is flatter or more carbonated, adjust it a little to compensate, but don’t get too carried away. As discussed below there are online calculators to help you do this. 

3. Sugar Type: There are a number of options available for priming, with the most popular being either dextrose (corn sugar) or plain white sugar (cane sugar). For the more adventurous, some additional character may be gained from using a number of other sugar sources, such as partially refined sugars (i.e. demerara), raw sugar, molasses, honey etc. 

The type of sugar you use will also influence how much you need to add. For example, you will need to add less cane sugar, which has an extract yield of 46 ppg, than dextrose, which has an extract yield of 42 ppg. Furthermore, not all sugars are equally fermentable and range from 50% for molasses to 100% for sugar and dextrose. Rather than going into great detail here I suggest you consult any good brewing book. John J Palmer’s How to Brew is an excellent choice and where I began my journey. 

To keep it simple, I highly recommend you use an online priming calculator. I find the one provided under the free list of tools in Brewer’s Friend to be very reliable and consistent with hand calculations. A good calculator will allow you to input the type of sugar, have some guidelines on the CO2 level to target, and allow you to input the temperature of the beer, thereby altering the residual CO2 level. Keep in mind that if your beer was warmer or cooler for a period of time it will have lost or taken up more residual CO2, respectively. This is where your senses come in handy and you can adjust the temperature input to manipulate the residual CO2 level to your best guess, based on experience. I do this often with my long-aged sour and wild beers which can be near to flat at bottling. 

Bulk priming and bottling

I recommend starting out by gently racking your beer from the fermenter to a CO2 purged bottling bucket with a tap and volume markings. Even better, you may have a set up that allows you to push the beer from the fermenter with CO2 pressure. If you don’t have CO2, you will probably be ok throughout this process as long as you take great care to avoid splashing, but be prepared for some beers i.e. hoppy styles to have a reduced shelf life.

Since your bucket has volume markings, you will know exactly how much beer you have to prime and package. Purge the bucket with CO2, blanketing the beer with a protective layer and close it up while you prepare the sugar. Now you can calculate exactly how much sugar to add. Weigh it accurately on some scales, add 25ml filtered water/L beer, boil it gently for 10 minutes and cool before gently adding the solution to the beer. 

The sugar solution is heavy and will not magically mix into the beer, so I recommend using a long sterile object, a spoon or wand from your racking cane or similar to create a gentle current. Mix gently and do not splash the beer or you will risk having oxidised/stale beer. Some oxygen will be used by the yeast during the conditioning, but not large amounts. When working with volumes of more than 30L, a thorough mixing of the sugar will become more difficult. I know of professional breweries that use pumps to circulate the beer and sugar in a mixing tank before bottling.  At home another option is to take a punt on your final volume and add the sugar directly to the bottling bucket prior to racking the beer, which then helps with the mixing. If you choose this route, it might be a good idea to hold back some of the sugar until the vessel is full, just in case you misjudged things. Once you are done it’s a good idea to blanket the beer once more with CO2. 

Somewhere along the way I picked up the approach of resting the primed beer to help it equilibrate. 15-20 minutes is all it takes and during this period you can take some notes and drink your gravity sample. Everyone does this right?

A bottling wand hooked up to your bottling bucket tap makes bottling simple. Start each fill gently to avoid splashing, fill the bottle to the rim and when the wand is removed a standard head space (air above the beer) will be created. Keep in mind that if you over or under fill this will impact the level of carbonation. Immediately after you fill each bottle place a sanitised crown cap on top. You can seal the cap right away, or like me, just keep filling and cap them when you are done or your bench is full. 

Once the bottle is capped it's a good idea to rinse away any spilled beer on the bottles, especially around the caps, as this can encourage the growth of mould. Box them up and then the wait begins. Conditioning your beer at 18-20oC is ideal for most styles, but some yeasts like those found in many Belgian styles are happy working warmer, with some brewers choosing to go down that route. A warm room, temperature-controlled fridge, cellar or similar with a favourable ambient temperature are all good options for the conditioning phase. Most standard beers will have a reasonable level of carbonation after a week, but they will not be finished. When approaching completion, the beer will start becoming clear from the top down as the yeast begins to settle out. 

How long should you wait? I find that it can take anywhere between 4-6 weeks for the beer to be fully ready with nice fine carbonation and no obvious sweetness from the priming sugars. If things are sluggish, a few gentle twists of the bottles can help rouse some of the yeast into suspension. Check the temperature inside the boxes, this can often vary (warmer or cooler) than the surrounding air temperature. I once had a wild beer that took 12 months to reach the desired level of carbonation, but it got there in the end. The Belgian brewers of lambic styles call this a lazy beer, but I was happy to wait, as the beer evolved beautifully in the bottle over time. So most importantly, be patient and enjoy the fruits of your labour. 

Cheers

About the author

Jamie is an award winning home brewer and the owner/operator of his tiny, part-time Dunedin brewery, Cell Division. His day job sees him working as a molecular biologist and neuroscientist at the University of Otago.

You will find Jamie writing beer geek articles for us which will no doubt feature his love of farmhouse and sour beers as well as providing useful advice on things such as yeast, fruiting, and other brewing techniques. We also have him working tirelessly on new recipes, diving into styles not previously featured in our catalogue and we may even convince him to dust off one or two of his award winning recipes for us.