FSIS formula

Brine concentration

The FSIS measure of how salty the water in a product is, which is the number the S. aureus and dry-cured ham thresholds are stated against.

FSIS gives the formula explicitly in its Trichinella compliance guideline: Percent brine = 100 x [salt] / ([salt] + [water]). The denominator is salt plus water, not the whole product. Fat is excluded, which is why the same cure gives a much higher brine concentration in a lean muscle than in a fatty one.

This is the number two published thresholds are stated against: 10 percent after equalisation to prevent Staphylococcus aureus enterotoxin production during warm drying, and not less than 10 percent for a dry cured ham made without nitrate or nitrite.

The formula, as FSIS states it

Parameters

Percent brine: 100 x [salt] / ([salt] + [water])
Denominator: salt plus water only
Fat: excluded

FSIS Compliance Guideline for the Prevention and Control of Trichinella and Other Parasitic Hazards in Pork and Products Containing Pork, FSIS-GD-2016-0002, Ham and Shoulder Treatment Method 4.

Thresholds stated against this figure

Threshold	Value	Source
Prevents S. aureus enterotoxin production during warm drying, after equalisation	10 %	Reiman et al. 1972, cited in FSIS-GD-2023-0002
Dry cured ham made without nitrate or nitrite	not less than 10 %	9 CFR 319.106(b)(4)
Minimum internal brine concentration by the end of drying, country ham method	6 %	FSIS-GD-2016-0002, Method 4

Calculate

Salt in the product (% by weight)

If you have sodium rather than salt, multiply sodium by 2.542.

Water in the product (% by weight)

Brine concentration

6.25 %

Working

FSIS: Percent brine = 100 x [salt] / ([salt] + [water])

= 100 x 4.00 / (4.00 + 60.00)
= 100 x 4.00 / 64.00
= 6.250 %

Below 10 percent. FSIS cites 10 percent after equalisation as the figure that prevents S. aureus enterotoxin production during a warm drying phase, and 9 CFR 319.106(b)(4) requires not less than 10 percent for a dry cured ham made without nitrate or nitrite.

Worked example

A finished dry-cured product measured at 4.0 percent salt and
52 percent water.

  100 x 4.0 / (4.0 + 52) = 7.14 percent brine

The same 4.0 percent salt in a wetter product, 68 percent water:
  100 x 4.0 / (4.0 + 68) = 5.56 percent brine

What this does not tell you

FoodData Central reports sodium, not salt. Multiply sodium by 2.542 to get sodium chloride: the ratio of the molar masses, 58.44 over 22.99.