I have a sodastream, and for the most part it makes great carbonated water. However, any time I try to use the flavoring syrups, my drink becomes completely flat. I do follow the instructions and only carbonate water (no pumping bubbles with the syrup already mixed in).

I've tried all techniques I could think of: stirring syrup into fizzy water, pouring fizzy water over syrup, pumping syrup into fizzy water without mixing. Basically, if I don't stir, all the syrup goes to the bottom of the glass, and if I do stir, the bubbles are gone. I've tried refrigerating the syrup, room temp, warming it. The best technique I have come up with so far is to add a little bit of carbonated water, pour in the syrup, mix that up, and then add the rest of the carbonated water. I like to believe this "loosens" the syrup so it mixes into cold water a bit better. However, even with this technique, the drink is flat.

Does anyone else experience this? Anyone have suggestions?

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    Have you tried adding the syrup to the bottle that you carbonate in, capping the bottle, and gently agitating the capped bottle to mix the syrup?
    – moscafj
    Mar 19, 2017 at 21:32
  • I haven't tried using a capped bottle to do the mixing. I'll give it a try and report back. Mar 19, 2017 at 22:31
  • I tried it, it was still flat. Anything else I can try? Mar 28, 2017 at 20:50
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    One possible suggestion - mixing, and agitation in general tends to de-carbonate - maybe you can try putting the soda and syrup into a tightly-capped flat-topped bottle (has to be able to take carbonation pressures), and invert a few times, letting settle between, to mix it. I've used this on hard-to-mix syrups, and the lesser agitation may help. As an aside, less headroom in the mixing bottle means less air for the carbonation to dissolve into - maybe that will force more to stay in the drink.
    – Megha
    Jul 7, 2017 at 20:28
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    Having never encountered this, I'd like to know how carbonated the water is before starting (how many "buzzes" does the sodastream make before stopping), and why all the "creative" methods for adding syrup instead of "pour it down the side of the bottle you carbonated in," the process recommended by the manufacturer.
    – Allison C
    Apr 29, 2020 at 17:58

5 Answers 5


The solubility of carbon dioxide in water is a function of several factors. The most important are time, temperature, pressure, and composition.

  • In order to maximize your carbonation, ensure everything is as cold as possible. The colder the liquid, the more CO2 you can dissolve in the liquid.
  • Secondly, you will need high pressure. The higher the pressure the more CO2. For example, if you leave an open bottle of carbonated water on your table, it will go flat. If you cap the bottle, it will maintain carbonation, but also build up pressure in the bottle. The higher the pressure, the higher the carbonation. Any "other gasses", like atmospheric oxygen and nitrogen in the bottle will effectively reduce the "partial pressure" of CO2, so you should remove that.
  • Pure water is easy to carbonate. Once you start adding "stuff" to it, it becomes more difficult. Soda concentrate contains flavors and sugar, all of which hinder the ability of CO2 to dissolve into the the liquid.
  • It takes time for the system to reach equilibrium. If one just pressurizes a bottle with CO2, it can take quite a while for it to actually dissolve into the liquid. Increasing the contact between liquid and gas (the surface area) speeds up the dissolution.

I don't know how a sodastream works, so if my suggestions can't be exactly duplicated, let me know. Can you add CO2 to the bottle without opening up to the atmosphere? The best process would be to, first, ensure everything is cold, and mix everything together. Pressurize the bottle with CO2. Cap it to maintain pressure and shake...a lot. Purge the pressure to remove any oxygen and nitrogen, and repressureize. Close the bottle and shake again and you'll notice the pressure decrease as the CO2 dissolves (squeeze the bottle). Top off the pressure and keep shaking and squeezing and repeat until it stays pressurized. Allow any foam to subside, and make sure there are no bubbles on the wall of the bottle before opening.

I make a lot of soda, but use a large cylinder of CO2 and Carbonator Caps, which screw on standard plastic soda bottles. With this I can make anything from 12 ounce to 2 liters at a time.


Tried an experiment today to make sure I liked their flavours before taking a plunge for the machine.

Sealed 2 litre bottle of Walmart Club Soda left in fridge overnight. Poured 500ml into a glass. Very bubbly indeed.

Added SodaStream Diet Cola concentrate... drink was substantially flat within 2 minutes even if covered.

Theory? Most commercially sold soft drinks contain phosphoric acid as well as the naturally occuring carbonic acid which takes time to develop from the CO2 injection. The SodaStream drinks may be suffering from being "too fresh". The commercial drinks are probably benefitting from "aging" in the bottle and are probably produced with an initially higher level of carbonation than we would find acceptable straightaway.

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    If it was truly an experiment, you would have a control case to compare to your test case. Try this again, but pour two glasses, and add the flavoring to only one. This way you can see if the flavoring has a direct affect on the ability of the liquid to faints in carbonation. Apr 26, 2020 at 2:31

I am a soda stream expert because I have made thousands of sodas in it. You need to have the water cold first off. I add a few ice cubes to my water before putting it into the soda stream for carbonation. Then carbonate the water. Next step most important add a teaspoon of lemon juice and lime juice each then add Torino flavors put cap on and invert bottle a few times. Trust me this is the best way and you will love it. The lemon and lime juice is a must it is the citric acid that’s missing from your homemade soda that is in all other sodas or a man made version of it anyways.


I have personal experince with the sodastream. i reccomend you CHILL your syrups before mixing. storage at room temperature is causing a loss of fizz. and also, NEVER try to add additonal artificial sweetner to the bottle. it will cause the bottle to erupt. if you want a good bottle, prechill the night before the bottle and keep the syrups chilled. the bottles differ in recommendations of storage but always use chilled syrup and water. its not the aging of the supermarket bottles, its how its mixed.


It has something to do with the ice. The ice that my refrigerator makes always flattens my drinks. However, using store-bought ice keeps them carbonated. It might have something to do with the impurities in our tap water reacting to an ingredient(s) in the syrup.

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    A lot of fridges now have a water purifier/softener built it. If you are getting that amount of impurities check your filter.
    – J Crosby
    May 5, 2020 at 14:56

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