Salt moves into meat by diffusion, so the time for it to reach the centre of a piece grows with the square of the thickness: a piece twice as thick takes four times as long, and three times as thick takes nine times as long. Rules that count days per pound approximate this, and the parent article’s rules do so inconsistently, so judge a cure by the thickest dimension and keep the parent’s times as a floor you do not go below.
Part of Large-Scale Smoking & Curing
Curing time is the time salt takes to diffuse from the surface to the slowest point inside a piece of meat, controlled mainly by the distance it must travel.
The Law Behind The Rule Of Thumb
Salt spreads through wet muscle by diffusion, which is described by Fick’s second law (Crank, The Mathematics of Diffusion, 1975; recalled). The result needed here is a scaling relation. For a slab of thickness d salted from both faces, the time to bring the centre to a given fraction of the surface salt level is proportional to
t ∝ d² ÷ D
where D is the diffusion coefficient of salt in that tissue. D depends on temperature, on the salt level, and on the structure of the meat: fat and connective tissue slow it, and it is faster along the grain than across it. Measured values exist in the meat-science literature, but I cannot source one here, so no absolute time can be derived from this article. What can be said is the ratio between two pieces of the same meat at the same temperature:
| Thickness ratio | Time ratio (the square) |
|---|---|
| 1.5 times thicker | 2.25 |
| 2 times thicker | 4 |
| 3 times thicker | 9 |
Cold slows diffusion further, because D falls as temperature falls, but the parent’s 35-40°F range is a compromise: warmer cures faster but allows spoilage organisms to beat the salt to the centre.
What The Parent’s Per-Pound Rules Do To This
The parent gives a dry cure of 2 days per pound of the thickest piece, and wet brine times of 3-4 days per pound for large pieces and 1-2 days per pound under 3 lbs. Weight is a poor proxy for thickness. For pieces of the same shape, weight goes as the cube of the linear size, so thickness goes as the cube root of weight, and the ideal time goes as the weight to the power two-thirds. Compare a 3-lb and a 15-lb piece of similar shape:
- weight ratio: 15 ÷ 3 = 5
- thickness ratio: 5^(1/3) = 1.71
- ideal time ratio: 1.71² = 2.92 (equivalently 5^(2/3))
- the parent’s dry rule: 2 days per pound gives 6 and 30 days, a ratio of 5
So the per-pound dry rule is steeper than the idealised law. Which end is wrong depends on the anchor: if the 3-lb figure of 6 days is right, the 15-lb figure is long (the law gives 6 × 2.92 = 17.5 days against 30); if the 15-lb figure of 30 days is right, the 3-lb figure is short (30 ÷ 2.92 = 10.3 days against 6). Since too short is the dangerous direction, do not take the small-piece figure as licence to shorten a cure. But shape changes everything: a 10-lb belly and a 10-lb ham weigh the same and differ greatly in thickness. The belly’s cure should be much faster, and the ham’s slowest point, deep near the bone, is the one that decides the time.
Three Inconsistencies In The Parent’s Wet-Brine Rule
- A cliff at 3 lbs. A 2.9-lb piece at 1-2 days per pound takes 2.9-5.8 days. A 3.1-lb piece at 3-4 days per pound takes 9.3-12.4 days. A weight change of 0.2 lb makes the time jump by 1.6 to 4.3 times (9.3 ÷ 5.8 and 12.4 ÷ 2.9), while the thickness changes by only (3.1 ÷ 2.9)^(1/3) = 1.02 and the ideal time by 1.02² = 1.05.
- Wet is slower for large pieces. The parent recommends wet brine for “faster, more even” curing, yet for a 15-lb piece its brine time is 45-60 days (15 × 3 and 15 × 4) against 30 days dry. Wet is faster only for small pieces: at 2 lbs the dry rule gives 4 days and the wet rule 2-4.
- Weight, not thickness. Neither rule says what to do for a flat piece.
I have not changed the parent’s figures. Until they are reconciled against a tested source, treat the parent’s times as the minimum for the weight, and add time for thick, bone-in or fat-covered pieces.
What You Need
- A ruler or calipers, to measure the thickest dimension through the centre, not the length
- A scale
- A cold space at 35-40°F and a thermometer in it
- A log of each piece’s weight, thickness, temperature, cure type and days, with the result
Method: Cure By Thickness
Step 1: Measure the thickest dimension of each piece and note the bone position.
Step 2: Start from the parent’s time for its weight as a floor. For a piece thicker than the typical shape for that weight (a fat ham, a short thick roast), lengthen it; for a flat piece, do not shorten it below the floor without evidence.
Step 3: Hold the cure at the cold temperature throughout; a warm spell speeds bacterial growth along with diffusion.
Step 4: Record the result in the log: saltiness, firmness through the centre, and any off smell near the bone. Build up your own table of what worked.
Common Mistakes
- Cutting the time for a “small” ham. It may be small by weight and still thick.
- Judging the cure by the surface. The surface is cured first and feels firm while the centre is not.
- Raising the temperature to hurry it. Spoilage near the bone, called bone sour, is what hurries.
- Mixing pieces of different thickness in one batch and timing the batch by the thinnest.
Safety
The centre of a thick piece is where a short cure fails
Salt reaches the centre last. If the cure is stopped early, the interior has not reached a safe salt level, and in dense meat held cold but unprotected, Clostridium botulinum can grow. The parent warns against curing large, dense pieces without saltpetre, which is a poison to be handled by exact weighing (see Cold-smoked sausages and bacon); this article gives no quantity. Never shorten a cure to meet a deadline. If the interior smells sour, sweet or off near the bone, discard the piece.
What’s Next
- Learn next: Shelf life expectations by method — how long finished product keeps
- Combine with: Dry cure ratios and rub formulas — the ratios the times apply to