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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.

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What dangerous bacteria? –  Aaronut Aug 1 '11 at 21:53
    
I do not know. But I remembered a news program where they warned that raspberries contained some kind of germs/bacteria that could be dangerous. Also I've been raised with the "need to pour boiling water over" frozen berries. The question is an aim to clarify the risk of not fully boiling the berries before blending, if any. –  Stella Aug 1 '11 at 22:06
    
What country are you in. Berry bacteria is not a common problem? Freezing stops bacteria multiplication, and since you normally consume smoothies immediately after making them there should be no problem even IF dangerous bacteria was present? –  TFD Aug 1 '11 at 22:10
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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 '11 at 23:07
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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? –  Jefromi Aug 1 '11 at 23:46
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3 Answers

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.

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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 '13 at 1:30
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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.

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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.

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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 '11 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. –  BaffledCook Aug 3 '11 at 16:13
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