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?

  • 1
    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 '17 at 21:32
  • I haven't tried using a capped bottle to do the mixing. I'll give it a try and report back. – user2913869 Mar 19 '17 at 22:31
  • I tried it, it was still flat. Anything else I can try? – user2913869 Mar 28 '17 at 20:50
  • I would try add water then syrup, shake then top up with water, shake again (with plastic wrap seal and thumb ) then inject fizzzz – Tony Stewart Sunnyskyguy EE75 May 17 '17 at 23:26
  • 1
    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 '17 at 20:28

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.

  • 1
    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. – Kevin Nowaczyk Apr 26 '20 at 2:31

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.

  • 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 '20 at 14:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.