If you are bottling your beer, you may want it to have some fizz when you eventually open them.
But how much sugar do you add?
This depends on a number of things, but one thing to consider is the bottle you are using.
Type of Bottle
You may not think it, but there is a difference between glass and plastic. Plastic expands slightly, so you need a little more sugar than if you are using glass bottles.
If you are using plastic bottles, up your sugar by 50%. So if you would normally use 1/2 teaspoon in each bottle, use 3/4. Or if you are adding your sugar to your bottling bucket, then if you were using 100g for glass bottles, use 150g for plastic bottles.
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New we really should not be talking about 1/2 teaspoon or even a teaspoon as there are lots of different sizes of teaspoons used for stirring tea, but that is not a size for priming sugar. It should all be referred to as weight. so 1tsp would be 5 grams. 1/2 teaspoon is 2.5 grams. But that is usually too small for most kitchen scales to measure.
Here's a tip if you have electronic scales and need to weigh 2.5g. Set up your scales, put a ramekin on the scales and do not reset it to 0. Take a note of the weight and then add 2 grams of sugar, then add a little bit more, if you go up another g, you've gone too far.
This is why most homebrewers sugar the whole batch as 100g is much easier to weigh out than 40 lots of 2.5g.
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Headspace
Another thing to consider is your head space in the bottle. Liquid cant be compressed, so CO2 will dissolve into it straight away if there is no headspace. Air can be compressed. If you have a bigger headspace, the CO2 created by the secondary fermentation first has to compress the air in the headspace before it can start to dissolve into the beer, so the bigger the headspace, the less fizz in your bottle. But you do need some headspace, so just try and keep it equal in every bottle to keep your fizz consistent.
Yeast Tolerance
If your yeast have already reached their alcohol tolerance before you bottle, then adding more sugar to the bottle wont do anything for fizz, but it will make it sweeter. Make sure you use a yeast that can deal with the extra sugar when bottling.
Sugar
Different sugars have different amounts of energy, and therefore the yeast when they consume it will create different amounts of CO2. e.g. You will nee to use 30% more Dried Malt Extract than if you used granulated (supermarket) sugar to get the same amount of CO2. If you are using dextrose, you will need about 10% more than granulated sugar to get the same result - but it will not add any sweetness.
Temperature
A colder liquid can hold more CO2, so if you open a bottle and its at room temperature, some of the CO2 would have already escaped into the headspace. However, when you chill the same bottle down, that CO2 is absorbed back into the beer.
If you find you have very lively beers when you open them and they have been in the fridge, they might be too cold and have too much CO2 dissolved back into the beer. Let them warm up a degree or 2 and you'll find it will be less like an eruption.
Style of Beer
Different beers should have different amounts of fizz. A lager should have more fizz than a real ale. An American craft beer should have more fizz than a real ale, but less than a lager.
So, here's a rough guide for how much sugar (Granulated Supermarket Sugar) to add for a 23 litre batch going into glass bottles:
Real Ale - 75g
American Style Craft Beers - 135g
Stout / Porter - 100g
Lager - 150g
Wheat Beer - 200g
Fruit Sour - 130g
Belgian - 100g
Experiment
You may need to experiment with the amounts of sugar you use to get the fizz that you want and this can take a few attempts to get it the way you want, but persist.
Exceptions
Weirdly, there is always at least one bottle in a batch that has little to no fizz and one the total opposite that explodes out as soon as you crack the cap. It's normal. We've all had it happen, and that's part of the fun of home brewing.
Over Priming
Don't be tempted to add more sugar to your bottles. You'll likely end up with a big mess as if one goes, it's likely to set of a chain reaction. So if in doubt, add a little less. Then next time add a little more till you get to the level of fizz you want.