TL;DR
Rinse a reusable straw the moment you finish the drink and run a straw brush through it from both ends -- the interior is a long narrow tube that no dishwasher can reliably reach, and a rinse alone leaves a film behind. The brush itself needs cleaning and replacing too, since a splayed or slimy brush no longer contacts the tube wall.
Why a straw is a hard shape
A straw is a tube roughly six to ten millimetres across and twenty centimetres long, closed on all sides.
Nothing about that is easy to clean. Water flowing through carries away thin liquid but does nothing to a film clinging to the wall, and there is no way to see inside.
The films that build up are exactly the sticky ones. Milk and cream leave protein and fat, smoothies leave pulp and starch, and sugary drinks leave a sticky layer that other residue then sticks to.
That is why the brush is not optional. Mechanical contact with the interior wall is the only thing that removes the film, which is the same reason narrow bottles need a bottle brush rather than a rinse -- see how to clean an oil dispenser bottle.
How do you clean a reusable straw?
Rinse it with warm water immediately after use, then push a straw brush through with a drop of dish soap, working from both ends so the whole length is scrubbed. Rinse it through with hot water and stand it upright to dry. Clean the brush itself at the same time and let it dry fully.
The routine
1. Rinse immediately. Warm water through the straw as soon as the drink is finished. Ninety percent of the problem is prevented right here.
2. Add a drop of dish soap. Put it directly on the wet brush.
3. Brush from both ends. Push the brush all the way through, then repeat from the other end. Straws are often slightly tapered or bent, and one direction does not clean the whole tube.
4. Rinse through with hot water. Run water through the straw until it comes out clear and does not feel slippery.
5. Stand it upright to dry. In a jar or a rack, so water drains out rather than sitting in the middle. A straw left flat holds a bead of water in the tube.
6. Wash the brush too. Every time. More on that below.
Metal, glass, silicone, and bamboo straws
Stainless steel is the most common. Durable, dishwasher tolerant, and it does not hold odor. Avoid chlorine bleach, which pits stainless steel and leaves permanent marks, and skip abrasive picks inside, which scratch and give residue something to hold onto.
Glass is easy to clean and has one great advantage: you can see whether it is actually clean. It chips at the ends, and a chipped glass straw should be discarded.
Silicone is soft, safe for children, and the hardest to keep fresh. It holds a greasy film and absorbs odors, exactly as silicone does everywhere else in the kitchen. Wash silicone straws in water as hot as your hands can comfortably stand with a degreasing dish soap, and air them uncovered if a smell persists. That behavior is covered in how to clean ice cube trays.
Bamboo and wood should never be soaked and never go in a dishwasher. Rinse, brush, and dry immediately. Bamboo straws split with age, and a split straw cannot be cleaned inside and should be replaced.
Can reusable straws go in the dishwasher?
Metal, glass, and silicone straws are generally dishwasher safe, but a dishwasher does not clean the inside of a narrow tube reliably. Spray enters the ends at best.
Use a straw basket or lay them in the cutlery tray, and treat the machine as a wash rather than as a substitute for brushing. Brush first, then let the dishwasher do the rest.
Bamboo straws should always be hand washed.
Cleaning the straw brush itself
This is the step almost everyone skips, and a dirty brush simply redistributes residue.
After using it, rinse the brush under hot running water and work a drop of dish soap into the bristles with your fingers, then rinse until it runs clear.
Squeeze the excess water out and stand it bristles up so it dries. A brush left lying in a drawer or in a wet sink stays damp and develops a smell within days.
Replace the brush when the bristles splay outward and no longer reach the tube wall, when the wire has rusted, or when it holds a smell after washing. A splayed brush is doing nothing useful.
Brushes are inexpensive and many straws come with one, so there is no reason to persist with a worn one.
Getting a stubborn film or smell out
If a straw still feels slippery inside after brushing, there is a film left.
Soak it in hot water with a generous amount of degreasing dish soap for fifteen to thirty minutes, then brush again from both ends.
For odor, either soak in one part white vinegar to three parts water for thirty minutes, or use a baking soda solution. Use one or the other, never both together, and never combine bleach with ammonia, with vinegar or any other acid, or with rubbing alcohol, since each of those combinations releases a toxic gas.
Rinse very thoroughly afterward with hot water, and dry standing upright.
If you cannot see through a straw held to the light, or the film returns immediately after washing, replace it. The same visual check applies to gaskets and seals on the lids that go with reusable cups, in how to clean jar lids and rubber gaskets.
Habits that keep it simple
Rinse at the sink, not later. A straw rinsed within a minute rarely needs more than a brush.
Carry a case, not a bare straw. A straw loose in a bag picks up lint and grit.
Do not put a used straw back in a bag wet. Damp plus enclosed produces a smell quickly.
Keep separate straws for milk and smoothie drinks. These leave the heaviest films, and knowing which straw needs a thorough clean saves time.
Check them in the light regularly. Holding a straw up to a window shows you what a rinse actually accomplished.
Straws sit in the same category as every other narrow, enclosed kitchen item -- the fix is always mechanical contact plus prompt drying, which is the through line of the guide to cleaning kitchen tools without damaging them.
Cleaning drinkware reduces residue and odor. It is not a food safety program on its own.
Source: USDA Food Safety and Inspection Service guidance on cleaning food contact surfaces
FAQ
How do you clean the inside of a reusable straw?
Rinse it with warm water immediately after use, then push a straw brush through with a drop of dish soap, working from both ends because straws are often tapered or bent. Rinse through with hot water until it no longer feels slippery, then stand it upright to drain and dry.
Can reusable straws go in the dishwasher?
Metal, glass, and silicone straws generally can, in a straw basket or the cutlery tray, but a dishwasher does not reliably clean the inside of a narrow tube. Brush the straw first and treat the machine as the wash rather than the whole job. Hand wash bamboo straws.
How do you clean a straw cleaning brush?
Rinse it under hot running water, work a drop of dish soap into the bristles with your fingers, and rinse until the water runs clear. Squeeze out the excess and stand it bristles up to dry. A brush left damp in a drawer develops a smell within days.
When should you replace a straw brush?
When the bristles splay outward and stop contacting the tube wall, when the wire core has rusted, or when the brush keeps a smell after washing. A splayed brush passes through the straw without cleaning it, which makes the whole routine pointless.
Why does my metal straw smell?
Usually a film of milk fat or smoothie residue left on the interior wall, or moisture trapped inside from being stored flat. Soak it in hot water with degreasing dish soap for thirty minutes, brush from both ends, rinse thoroughly, and dry it standing upright.
Are silicone straws harder to clean than metal ones?
Yes. Silicone attracts oil and holds a greasy film, and it absorbs strong odors, which stainless steel and glass do not. Wash silicone straws in water as hot as your hands can comfortably stand with a degreasing dish soap, and air them uncovered if a smell lingers.
Reusable drinkware takes a minute a day. The kitchen around it takes longer. If you would rather hand that off, get a quote or read more about house cleaning services.