Hot fill vs cold fill

Hot fill

The product is cooked, filled hot and capped, and the heat sterilizes the container and its closure. Packaging makers list it for noncarbonated drinks, juices, sauces, sports drinks and teas. The container has to withstand the heat and the vacuum that forms as the product cools¹, which is why hot-fill lines run glass and heat-set plastic.

University of Minnesota Extension publishes hot-fill-hold times for smooth cottage-food products at pH 4.1 or lower, such as barbecue sauce²:

Between pH 4.1 and 4.6 those holds do not apply, and a different thermal process is needed³.

Cold-fill-hold, for shelf-stable products

The product is filled at room temperature and made safe by acid, then held warm so the acid can act before the product is released. Minnesota's guidance requires a final pH of 3.3 or lower. pH 3.5 is acceptable with 2.5% acetic acid, and pH 3.8 with 2.5% acetic acid plus 0.1% benzoic acid. Bottles are held at least 6 days at 50°F or above. It suits products that lose quality under heat, such as mustard or certain sauces⁴.

These processes are validated with challenge studies. Food safety researchers recommend that a study show a 5-log pathogen reduction over four or more sampling times in at least two independent trials, with pH measured each time⁵.

Refrigerated cold fill

Filled cold and kept cold. Foods stored, distributed and sold under refrigeration are excluded from FDA's definition of an acidified food⁶, so the acidified food rules do not apply, but the product needs refrigeration all the way to the shelf and its shelf life is limited.

Which one fits your product

• A smooth sauce at pH 4.1 or lower, sold shelf-stable in glass: hot-fill-hold is the process the guidance describes².
• Heat hurts the flavor or texture, as with mustard or some sauces, and the recipe can reach pH 3.3 to 3.8 with added acid: ask about cold-fill-hold⁴.
• Fresh flavor matters most and you can sell refrigerated: refrigerated cold fill, or HPP.
• Low-acid (above pH 4.6) and shelf-stable: neither one. That product needs retort or aseptic processing⁷.

The figures above come from cottage-food guidance. A commercial plant runs the process your process authority sets for your exact recipe and container.

In this directory, 50 plants state hot fill and 41 state cold fill on their own websites; 32 state both. Cold fill here means the plant names cold filling, so ask which kind it runs.

Sources

1. Graham Packaging, Product Fill Types (Company; read through a search summary, the page itself was not opened in full)
2. University of Minnesota Extension, Preserving food using hot-fill hold (University)
3. Breidt et al., Thermal Processing of Acidified Foods with pH 4.1 to pH 4.6, Food Protection Trends (2014) (Standards body)
4. University of Minnesota Extension, Preserving food using cold-fill hold (University)
5. IAFP, Recommendations for Designing and Conducting Cold-fill Hold Challenge Studies (Standards body; read through a search summary, the page itself was not opened in full)
6. 21 CFR 114.3, definitions for acidified foods (Cornell LII) (Government)
7. 21 CFR 113.3, definitions for low-acid canned foods (Cornell LII) (Government)