by Sherida Phibbs, UCCE Master Food Preserver
Question: I know what I am about to ask is not safe canning, and I am not planning on doing it. I just want to know the science behind it. If I make relish from fresh cucumbers with vinegar and sugar, and put lemon in it to increase the acidity – what is the difference between water bath canning versus using a lid sealer hand pump?
Answer: Thank you for your thoughtful question—and for being clear that you’re not planning to try this method but are simply looking to understand the science. That’s exactly the kind of curiosity we love to encourage!
The role of water bath canning is to kill spoilage organisms (like yeasts, molds, and some bacteria) that may be present in the jar or on the food, and to ensure a strong vacuum seal by heating both the product and the jar. For low acid foods, pressure canning is required to destroy clostridium botulinum.
Now, regarding the hand-pump lid sealer: these devices create a vacuum without heat. While they may remove some air and "pull" the lid down, they do not kill any microorganisms. Without heat, any yeast, mold, or bacteria that might be in the relish—or introduced by the utensils, jars, or environment—can still thrive, even in an acidic environment. Some molds and yeasts are acid-tolerant, and even if they don’t cause illness, they can still spoil the food or affect flavor, color, or texture.
Here’s a summary of the key differences:
| Process | What It Does | What It Doesn't Do |
| Water Bath Canning | Kills spoilage organisms, heats contents to ensure a vacuum seal, removes air | Does not sterilize like pressure canning, not suitable for low-acid foods |
| Hand Pump Sealer | Removes air to create a vacuum (sometimes) | Does not kill microorganisms or heat the product, so spoilage risk remains high |
Also, while you’re adding vinegar and lemon juice to increase acidity—which is great—the ratio and tested recipe matter. That’s why we always encourage using tested recipes: they’ve been developed to balance pH, density, and heat penetration to ensure safety.
Thanks again for asking a smart question. Understanding the “why” helps all of us become better and safer preservers!