The first thing to consider is how much you are looking to add in terms of CO2 volume. If priming a stout, you will not be adding much sugar at all and it is excusable to me to use white sugar, the cheapest of all priming ingredients. On the other hand a stout has a massive flavour skeleton which can hold the addition of robust flavours. It is the perfect beer to be experimenting with other priming sugars that will have perhaps higher unfermentables.. You can use black treacle, golden sugars, unrefined sugars dark or light, muscavado, Molasses, golden syrup, maple syrup, the list goes on and on. You can even make your own syrups from liquidised raisins, sultanas, any dried or fresh fruit at all if you are adventurous.
If you choose to make your own syrup you will need to assess the sugar content. After filtering/sieving the syrup you will need to take a sample aiming for around 1.040 gravity. You can use a refractometer but it's quite easy to test your syrup with a hydrometer. This test can also be used with your honey if you want to know exactly how much sugar/water content is in your honey (see honey section below!)
As a reference point we know that 9g of household sugar dissolved in 91g of soft water ( hard water marginally different but not worth worrying about) results in a sugar solution gravity 1.040.
When you dissolve your 9g of honey or syrup into the 91g of water and you get your gravity you can then calculate the sugar content versus your sugar yardstick. This is because to all intents and purposes up to our test levels the gravity scale behaves pretty much in a linear fashion.
So if your honey brings a reading of 1.028, which is the likely result given honey has a steady level of sugar 70 per cent of that of granulated sugar gram for gram, the calculation is 28/40 to get the fraction of sugars compared to granulated.
Working ahead if the online calculator is entrenched in referring only to malt extract or granulated sugar, get the figure recommended for granulated sugar and divide that figure by the fraction to get the total amount of syrup you need equivalents.
I use the calculator at http://www.kotmf.com. There is also an invaluable priming guide for each world beer style to help you on your way. Bear in mind everyone likes their beer their own way so you will be best advised to prime , record and adjust to your own style. Write it down! Most people's batch sizes become consistent so you will not need to refer to priming calculators in the future if all things are equal.
Honey specifically
Honey is pretty consistent. But it can vary between 14% and 18% water. This is not a difference that could result in bottle bombs. More likely, the bombs are because people get confused about calculations. OR because people do not heat their honey to 80 degrees C first to kill the wild yeast present. IF YOU DO NOT HEAT TREAT YOUR HONEY YOU WILL GET BOTTLE BOMBS. YOU HAVE BEEN WARNED. Obviously allow to cool before priming. The general rule of thumb is whatever granulated white sugar you would be using to prime you divide that amount by 0.7 to get to your honey priming level. The multiplier only varies by 0.04 with high or low water content so it's quite irrelevant.
If you wish to get a feel for water content, one clue can be crystal content at room temp, though beware if a honey has suffered cold as it will be more crystalline from storage conditions. The second indicator if you have two honeys side by side in the supermarket is how fast the bubble of air rises when you tip them upside down at the same time. The runny honey bubble will rise fastest and have less sugar. You can obviously test your sugars with a hydrometer too -see above. Most though not all honeys now have nutritional information an d calorie content is pretty much the same as sugar content when you compare honey versus white sugar. So if you get a cal figure per 100g use that versus the value for granulated sugar (392kcal per 100g). It should produce your fraction in the region of 0.7. This is an acceptable comparison when assessing honey because its sugars are 95% fermentable (i.e.nearly 100% like White sugar) The best way to assess other ingredients is using the calorie comparison for sugars on the nutritional information. Most dried fruit will produce a syrup high in fructose which is highly fermentable too. In contrast, black treacle is 64% sugar and quite high in unfermentable sugar so it has a little over 50% of the fermentable power of white sugar by mass..
Priming with syrup.
The syrup must be heated to ideally 100C to kill most bacteria, but at 80C you will still kill most bacteria and all yeast and still retain more volatile flavour compounds.
When you batch prime with syrups you want to avoid stirring too much which can oxidise the beer but you definitely need the syrup to mix in thoroughly otherwise you will get some bottles overprimed some underprimed which we don't want. To ensure that the syrup is thinner I will water it down before heat treating and add while it is still quite warm, say 60C. The effect of adding even 1L of extra water will be minimal to a 40L batch ( but should still be noted in calculations), but ensures consistent priming is achieved. The temperature rise will not be sufficient to shock the vast majority of the yeast because the heat will dissipate quickly. Pour it slowly close to the surface of the beer and in circles. Stir the beer very gently but deeply with a sanitised long slotted spoon or similar. Do not create bubbles on the surface of the beer if you can help it
Malt extract
There are numerous extracts on the Market. It is important to know how fermentable it is. Muntons is 75% and most people use this brand I know of. If you are using anything else check the packaging and use the right extract in the online calculator. If you are using liquid malt extract this is 20 per cent water. So you will need to divide the dry malt extract dose by 0.8 to arrive at your required dose of lme. The reason to use malt extract is it keeps the malt balance of the beer if you don't want variation to the beer from non malt sugar. Neither approach is wrong or right but it depends what you are trying to achieve. If you want to go one step further you can use your original wort to prime......
Priming with the same gyle
When you get to the end of the boil you can take off the amount of wort you need to prime the end batch and keep it frozen until you need to prime. This gyle has not been inoculated with yeast. You know the OG don't you from your post boil reading. There are online calculators at Brewzor to help you wou work out how much of your final volume to take off to freeze. By the way, sanitised plastic milk containers are good for freezing in but don't fill to the brim - allow for expansion.
Here's a handworked example.
Wort at OG 1.040, 42 litres. Take 2litres off for priming.
At fg say of 1.010 you will be adding 2 l of 1.040 to it. The equivalent mass of white sugar theoretically in 2l of that gravity is more or less 1to10 so 180g (2000ml divided by 11). Because gyle is 75% fermentable ( generally - though use you OG and FG to work out your own wort fermentability), the equivalent sugar dose from that gyle addition is 135g only and remember total beer volume is now 42litres with the addition! If you want to prime a little less when you have your online calculator recommendation you can reduce your gyle addition accordingly. Obviously you can't add more than you have so take off sufficient at the outset! For reference 135g is a good priming level for most British ales of a *35l* batch size.
Clearly the gyle has the same hoppiness too. Don't constrain yourself to towing the line though. Priming is the perfect time to add subtle flavour to beer because most of the fermentation is done. One thing is for sure, the more variation you make to your beer the more likely it is that it will be unique to you. There is nothing more satisfying than that.
Go and explore the world of priming.
