How to Keep Coffee From Going Sour in a Thermos

series object on white - thermos bottle image by Aleksandr Ugorenkov from

For many people there is nothing better than a hot, fresh cup of coffee. Whether you are riding a commuter train on your way to work or out for a morning walk, having your favorite cup of java with you can often be the difference between the start of good day, or a bad one. While it may be easy to keep the coffee hot, keeping it fresh is another challenge, one that depends on the type of container you buy and how you maintain it.

Select the right thermos for your coffee. Buy a food-grade, stainless-steel thermos that will stand up to frequent use. According to Fante's Kitchen Wares, food-grade stainless steel "is one of the most hygienic surfaces for the preparation of foods and very easy to clean, as its unique surface has no pores or cracks to harbor dirt, grime or bacteria."

Thoroughly clean your thermos with very hot, soapy water after you buy it, and clean it again just before you use it for the first time. Alternatively, use very hot water and vinegar to clean the thermos. Some thermoses allow to you to remove the bottom for a more thorough cleaning. Depending on your model, there may be breakable materials -- such as ceramic or glass -- inside. Handle it with care; the thermos will shatter if you drop it.

Fill the thermos with boiling water before pouring your coffee into it. Boil a kettle of water and fill the thermos to the brim. Let it sit for three to five minutes, pour it out, then immediately pour your coffee into it. Not only will the boiling water kill any bacteria that may be in the thermos, it will also heat it up so your coffee doesn't cool when it is poured into it.