Steristar Steam-Air Retort – FDA Guide

Container Machinery has provided machinery for food processing for over 40 years.  The original company (Container Machinery Corporation) was founded in 1974 and manufactured the Truxton Steristar Steam-Air Retort.

Truxton Steristar Steam-Air Retorts
Truxton Steristar Steam-Air Retorts installed in a facility

FDA: Guide to Inspections of Low Acid Canned Food 39 | Steam-Air Retorts

Equipment and procedures for processing in steam-air retorts are not specifically covered in the lacf regulations. These systems are covered by 21CFR 113.40(j), Other Systems. “Other” systems are required to conform to the applicable requirements of the lacf regulations…

…At one time the Container Machinery Corp. built the Truxton Steristar in the U.S….

The steam-air retort uses a mixture of steam and air, which is added to create an over-pressure in the retort. The air over-pressure allows thermal processing of a wide variety of containers including: glass, metal cans, rigid plastic, and flexible pouches. Steam-air mixtures, although in a gaseous state similar to 100% steam, when used as a heating medium behave more like water…

…It is very important to maintain the correct steam-air ratio in this type of retort. The steam-air ratio should be the same as that used during studies to determine temperature distribution in the retort.

Steam-air retorts are normally operated at steam-air ratios ranging from 75% steam/25% air to 95% steam/5% air, depending upon the air over-pressure in the retort. The steam-air ratio is normally determined by the processing temperature and the type of package being processed.

The pressure in a steam-air retort must be maintained at the correct pressure to prevent container distortion and to maintain the correct steam-air ratio…

…The percent steam can be calculated using the following formula:

Steam pressure psia (pounds per sq. inch actual) = % steam

Total system pressure psia

Steam pressure psia is determined by determining the amount of steam pressure generated at a certain temperature [e.g. 240° F generates 10 psig (pounds per sq. inch gauge)] plus 14.7 psi (atmospheric pressure at sea level) equals 24.7 psia. The total system pressure is determined by taking the gauge reading and adding 14.7 psi. A steam air system having a total gauge pressure of 15 lbs operating at 240° F would have a 83% steam, 17% air mixture.

10 psig + 14.7 psi atmospheric = 24.7 = 83% steam

15 psig + 14.7 psi atmospheric    29.7

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