Shelf-stable canned butter is currently available in retail stores, and many home-preservationists promote home-canning of butter. Non-cultured butter is a low-acid canned food, which would presumably require thermal processing. The lack of a thermal process step in canned butter products raises questions of potential safety, because they are hermetically sealed and generally exhibit anaerobic growth conditions, which are optimal for Clostridium botulinum growth. Without thermal processing, low-acid canned foods (LACF) must have inhibitory factors present to prevent C. botulinum growth. Some potential intrinsic inhibitory factors, or "hurdles", within butter include: reduced water activity (aw), acidity (pH) in cultured products, elevated salt content, and the micro-droplet nature of the aqueous phase in the butter emulsion. It was hypothesized that a normal intact butter emulsion would have sufficient "hurdles" to prevent C. botulinum growth, while a broken butter emulsion would result in a larger aqueous phase that would allow for growth. Butter was prepared using a batch churn method with either inoculated or uninoculated cream. Butter samples with four different salt amounts (0, 0.8, 1.6, & 2.4% added NaCl) were prepared and placed in coated aluminum cans for storage. Samples were stored for 1 or 2 week periods at either 22°C or 41°C and then plated for C. sporogenes growth. Samples stored at 41°C showed a significant increase over those stored at 22°C. This growth increase occurred due to incubation near the optimal growth temperature for C. sporogenes and damage to emulsion structure. Furthermore, sodium chloride (NaCl) addition was found to have a significant effect on C. sporogenes growth, with 0.8 % NaCl promoting more growth than 0%, but with decreases in growth beyond 0.8%. Uninoculated control plates were also found to have bacterial growth. This growth was attributed to other anaerobic bacteria present within the cream. It was concluded that removal of the butter structure "hurdle" could result in C. botulinum growth even at elevated salt levels and therefore home preparation of canned butter is not advisable. It is also possible that commercially canned butter, if heat abused, could potentially allow for C. botulinum growth and therefore consumption is not recommended.



College and Department

Life Sciences; Nutrition, Dietetics, and Food Science



Date Submitted


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Canned Butter, Clostridium botulinum, Clostridium sporogenes