Shared Equipment: What Actually Transfers

Almost every plant runs more than one thing on the same equipment, and almost every kashrus question in a plant comes back to the same principle: heat moves status, contact does not.

Getting that one idea straight resolves most changeover questions before they reach anyone.

The principle

Taste absorbed into equipment moves into the next product when heat drives it. Cold contact, on its own, does not transfer.

So the questions that matter about any piece of shared equipment are:

• How hot does it get, and at what stage?
• Is there liquid involved, and is anything under pressure?
• How long does product sit in contact with it?
• When did it last run the other product?

Notice what is not on that list: how well it was cleaned. Cleaning is necessary and it is not the same question. Cleaning removes food; it does not remove what the walls absorbed.

Cold is genuinely different

Equipment that only ever handles cold product is a much lighter question, and plants often do not realise how much lighter.

Two qualifications keep it honest.

Soaking. Cold contact over a long enough period does transfer — kavush, reckoned at twenty-four hours. Product sitting in a tank, a tanker or a line overnight is not the same as product passing through.

There is a neat consequence worth knowing: because transfer by soaking only completes at twenty-four hours, and a vessel's absorbed taste has deteriorated by that same point, the two effects arrive together. That is why the analysis of long cold holds is more forgiving than people expect — but it is also exactly the kind of reasoning to have confirmed for your situation rather than applied yourself.

Regular use is treated differently from occasional use. The Rema holds that one should not regularly use a vessel of prohibited material even cold. Occasional use is a different matter. A production line running your product every week is regular use by any reading.

The twenty-four hour rule in a plant

Equipment used within the last twenty-four hours is ben yomo — the absorbed taste is still considered good. After that it is aino ben yomo, and the taste has deteriorated.

This matters commercially because it is often the cheapest variable you control. A changeover scheduled after a gap is a different proposition from one scheduled immediately, and scheduling is free where kashering is not.

Two cautions. The practice is not to kasher equipment while it is still ben yomo, so a kashering usually needs the gap anyway. And a rabbinic requirement to kasher may still apply even to aino ben yomo equipment — the deterioration is not a general exemption.

What this means for your line

The practical shape of a good arrangement is usually one of four:

• Dedicate the equipment. Cleanest, most expensive, and worth it where the product justifies it.
• Sequence production. Run the more restricted product first after a kashering, then the less restricted. Costs scheduling discipline rather than capital.
• Kasher between runs. Real cost and real downtime, and the method depends entirely on the equipment.
• Establish that nothing transfers — where the process is genuinely cold, or the contact genuinely brief. This is the cheapest outcome and the one most worth investigating before assuming you need one of the others.

Which applies to your equipment is a question of temperatures, times and materials, and it is the sort of thing to establish at the design stage rather than after the line is built.

See also steam systems and shared boilers.