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I will soon receive a few kg of fresh boar bones. From these, I want to make bone broth and preserve them in Weck jars, as I don't have a freezer.

Unfortunately I do not have a pressure cooker of any kind. What's my best bet to minimise the risk of spoilage or botulism? How long can I realistically keep the preserved bone broth?

I've read about some approaches boiling the jars twice with a two day wait at room temperature in-between, killing the C. botulinum bacteria as they leave their spore stage. However, I'm not sure if that'll actually do the trick.

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    You can’t make it shelf stable without a pressure canner. You can put it into sterilized jars while hot with enough animal fat to form a cap when it cools and then store it in the fridge for a week, but that won’t protect against botulism. You can also reduce it to Demi-glacé consistency to reduce the freezer space required
    – Joe
    Commented Nov 19, 2022 at 23:11
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    As there's been a bit of confusion in the answers, should we assume that there is no freezer available to you? That's as opposed to the case where there is a freezer, but it's too full, which is how some people seem to have interpreted the ambiguous "lack of".
    – Chris H
    Commented Nov 21, 2022 at 11:12
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    @ChrisH No freezer available at all. Sorry for the confusion.
    – FUZxxl
    Commented Nov 21, 2022 at 11:18

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You cannot do this safely without a pressure canner (not pressure cooker). Freezing is probably your safest and easiest option, if you don't want to invest in a pressure canner. To save space, cool the broth, then transfer to freezer style zip lock bags and freeze flat. This would also decrease thawing time. Another space saving tip is to reduce your finished stock by 1/2 or more, concentrating your product. Then add water when you use.

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  • I do not have any freezer space at all unfortunately.
    – FUZxxl
    Commented Nov 19, 2022 at 17:25
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When canning to make shelf-stable finished product, you must follow tested recipes directly to ensure proper preservation -- following both the method and processing time carefully.

To preserve stock/broth safely you will need to use a pressure canner. This method of food preservation is used because the food item is meat-based and low in acidity.

I'm not aware of any other method to make stock/broth shelf stable & meet food safety guidelines.

Your options are to either pressure can or to freeze. Any other method will not guarantee that stock/broth will be safe to leave at room temperature.

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  • Funnily enough, the German institute for risk assessment recommends the boil-twice method to prevent botulism. Pressure cookers are not wide spread over here in Germany.
    – FUZxxl
    Commented Nov 21, 2022 at 11:52
  • @FUZxxl, I can't read German, and I'm not familiar with German food safety guidelines. If they provide an additional option, then it very well may be valid. But I'd only consider published canning recipes by trusted sources, backed by food safety guidelines
    – AMtwo
    Commented Nov 21, 2022 at 12:23
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    I've added a translation in another answer - far too large for comments - with a note as to what authority they carry. - & yes, the same in the UK. Home canning is just not a thing here, most equipment you can get is imported from the US, with constant guides & notes on how to convert things to metric ;)
    – Tetsujin
    Commented Nov 21, 2022 at 16:37
  • @Tetsujin Home canning is having a rennaissance in Germany. However, the traditions and practices vary from what they do in the US. For example, pressure canning is largely unheard of for private use. Cans are stored in cold basements, retarding germ growth further.
    – FUZxxl
    Commented Nov 21, 2022 at 17:59
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Using the answer space to provide translation of the German government document.

The document is from the Federal Institute for Risk Assessment -

a body under public law of the German federal government with full legal capacity. The institute comes under the portfolio of the Federal Ministry of Food and Agriculture (German: Bundesministeriums für Ernährung und Landwirtschaft, BMEL) and has the task of providing scientific advice to the federal government on issues relating to food safety, product safety, chemical safety, contaminants in the food chain, animal protection and consumer health protection.

Only the relevant section is below, the rest is background info.

For physical reasons, the maximum heating limit of 100 degrees Celsius (boiling water) cannot be exceeded. The same applies to the so-called cauldron preserves from domestic and rural slaughter, since here too a temperature of 100 degrees Celsius is not exceeded during heating. If you want to preserve meat or vegetables such as beans, you should always heat the food twice to 100 degrees Celsius within a day or two. Between the two heating processes, the preserves should ideally be stored at room temperature. During the first heating, the bacteria capable of reproduction are killed and the spores can germinate and develop into bacteria capable of reproduction. These can be killed with the second heating.

If, despite all precautionary measures, botulinum toxins have formed during storage, they can be inactivated by boiling the preserving goods to 100 degrees Celsius immediately before consumption, as the toxins, unlike the spores, are sensitive to heat. At a heating temperature of just 80 degrees Celsius, several minutes are required for inactivation.

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    Good reminder about the fact that for botulism, specifically, boiling the food before consuming it denatures the toxins - botulism in stored foods is thus easily defeated by cooking the stored food before consuming it.
    – Ecnerwal
    Commented Nov 23, 2022 at 19:38

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