I often like to make smoothies where I among other things add frozen berries. I boil some water in my tea-boiler and pour it over the berries before I add them to the smoothie mix. Is this enough to get rid of the dangerous bacteria, especially found in raspberries?

Ps. Recipe is: Vanilla soy-milk . Banana . Berries . Orange (to keep the banana from turning brown)

Blend until smooth.

  • 15
    What dangerous bacteria?
    – Aaronut
    Aug 1, 2011 at 21:53
  • 3
    Hard to say without knowing what kind of bacteria, and how much. Cooking almost never kills every single individual bacterium, it's a question of safety thresholds. If you have reason to believe that the fruit is contaminated, but don't know any more details, then nothing short of boiling it into purée is truly safe. On the other hand, if it's safe to eat right out of the bag (which is normally guaranteed and enforced by government food agencies) then boiling water is just a waste of time, water, and perfectly good fruit.
    – Aaronut
    Aug 1, 2011 at 23:07
  • 1
    What do you do when you get fresh berries? Presumably you wash them and eat them, right? Are you assuming that these frozen berries are somehow more contaminated?
    – Cascabel
    Aug 1, 2011 at 23:46
  • 1
    I'd also suggest that, in general, NO, pouring boiling water over them wouldn't kill the bacteria (if present) for the following reasons: 1) would be surface-only, 2) would rapidly chill below the kill zone due to the temperature of the berries, and 3) would not be in contact long enough at a high enough temperature. Look at pasteurization (which doesn't actually sterilize, it only kills off enough pathogens to make the food "safe") - it requires a temperature of 275 degrees F (135C) for at least one second. That's well above the boiling point. At 160F (71C) you need at least 15-20 sec. Aug 2, 2011 at 3:00
  • 2
    Recently in Sweden there has been a lot of talk about the parasite "Dvärgbandmask" (sorry, don't know the English name). It is a small worm carried by foxes and such. Berries picked in the woods can be contaminated, even though it is highly unusual. The disease that this parasite can cause in humans is extremely dangerous, and there is no cure. In the past these worms did not exist in Sweden, only further south in Europe (Denmark?) but last year they started appearing in Sweden too. Anyway, if you want to be 100% safe from these guys you have to cook the berries properly. Aug 2, 2011 at 8:17

4 Answers 4


From the comments, Henrik noted that there is a parasite in Sweden (called "Dvärgbandmask" in Swedish) that contaminates wild fruit. This is a type of tapeworm called "Echinococcus" in English. Its eggs can cause a parasitic disease called Echinococcosis or hydatid disease. According to this article, freezing the eggs to very low temperatures and/or freezing the eggs very rapidly is fatal to them. Given that modern "IQF" freezing methods for berries bring the fruit very quickly to below -20°C, I'd say that the danger from echinococcosis is very low (much lower than eating unwashed fresh fruit).

As for risks from bacteria, these are also very low because the process of preparing the fruit for freezing and then subsequently freezing them kills the majority of any present bacteria.

  • 1
    It should be noted that most parasites are killed by freezing for more than 7 days - hence the only real requirement for "sushi-grade fish."
    – Matthew
    Jun 27, 2013 at 1:30
  • Could it be what is normally called a fox tapeworm? Known risk with wild berries... Jan 22, 2018 at 15:15
  • @rackandboneman Yes, it looks like it might be the same, or at least related.
    – ESultanik
    Jan 23, 2018 at 23:29

Raspberries seem fairly acidic, and many bacteria don't stand up well to acid. Here's one article that says raspberry juice kills bacteria. If you're worried, then, you might consider pureeing the raspberries in your blender and letting them sit for a minute before adding the yogurt, banana, or whatever else you put in your smoothies.


No, you should boil for at least 1 Minute.

Food Safety Authority of Ireland states the following in May 2017, especially for imported berries:

As a result of outbreaks of norovirus and hepatitis A virus in imported frozen berries across Europe in recent years, the FSAI recommends boiling imported frozen berries for one minute before consumption.

See FSAI : Berries - Advice to boil imported frozen berries (May 2017)


McGee has an article for conserving fresh berries for some days longer. He talks about molds, not bacteria...

Frozen berries should be alright as your country's health regulations will not allow dangerous foods to be imported or produced or sold.

  • 1
    The goal of health regulations is to not allow them ... but many countries have had problems with pathogens that were believed to be in the items (eg, tainted water used to grow spinich in the U.S, the bean sprout incident in Germany where they think it might've been in the seeds). The only advantage to frozen over fresh in this case is that if it's sold frozen, it's packaged with tracking numbers, so it's easier to identify the source if there's a recall.
    – Joe
    Aug 3, 2011 at 14:03
  • The number of cases is so small you should ignore the risk. Tons of food, frozen, fresh, dehydrated, you name it, is sold around the world and less then 100 people have died of one localized incident. Not that that's not serious, but you really should consider food bought in shops as safe. Aug 3, 2011 at 16:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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