A challenge study is a lab test that adds the pathogens a food could carry, such as Listeria, Salmonella or Staphylococcus, holds the food the way you plan to sell it, and measures whether they grow. You need one when the Food Code's pH and water activity tables mark your food "PA", product assessment required. A PA food is treated as time/temperature control for safety (TCS): kept cold, kept hot, or sold under time as a public health control, until a study shows it doesn't need to be. The study goes to the health department with a variance request, and if accepted, the food can sit out as long as the study supports. Before paying for one, check the cheaper ways out: time control covers up to 4 hours, or 6 from cold; wrapping a baked food right after baking moves it to the Food Code's other table, where more foods come out non-TCS; and some foods can be reformulated, though adding vinegar or another ingredient to make a food non-TCS needs a variance too. The protocols retail studies follow come from a national advisory committee's parameters, through the Conference for Food Protection; a university or private lab designs and runs the study. In the example below, a Waco kolache shop gets a study for its cream cheese kolaches.
The short version
- A challenge study adds pathogens to a food, holds it as you'd sell it, and checks for growth.
- You need one when the Food Code tables say PA, product assessment required.
- Until then a PA food is TCS: cold, hot, or time control.
- The study supports a variance from the health department, for a set holding time.
- Cheaper options first: 4 hours of time control, wrapping right after baking, or a recipe change.
- Making a food non-TCS with vinegar or an additive needs a variance too.
- TaroStack keeps each recipe by weight, so the study's recipe stays the recipe. More below.
When you need one
| Food Code result | What it means | Your options |
|---|---|---|
| Non-TCS | No time or temperature control needed | None needed |
| PA, product assessment required | Treated as TCS until shown otherwise | Keep cold or hot, time control, change the food, or a study |
| Named TCS food, such as cooked meat | TCS | Keep cold or hot, or time control |
The tables themselves, and which foods are named TCS, are in TCS foods list; measuring the numbers is in water activity for food makers.
The rules
| Rule | Where |
|---|---|
| The tables | Table A for food heat-treated and then packaged, table B for food not heat-treated or heat-treated but not packaged; PA means product assessment required (Food Code 2022, 1-201.10) |
| Product assessment | A PA food shown to preclude pathogen growth, by its own makeup, its packaging, storage or use, isn't TCS (1-201.10) |
| The variance | A PA food is TCS until studies show otherwise, with a variance request to the regulatory authority; a challenge study can set the time at room temperature (Annex 3) |
| Time control | Up to 4 hours, marked and then discarded; up to 6 hours from 41°F or less, staying at or below 70°F (3-501.19) |
| Additives and vinegar | A variance before using them to preserve a food or make it non-TCS (3-502.11(C)) |
This is general information, not legal advice; states adopt the Food Code with their own changes.
An example: the cream cheese kolaches
Brazos Kolache Shop, the made-up kolache shop in Waco, Texas, I use in these examples, bakes at 5 a.m., opens at 6 and sells from an open case until about 1. A health inspector asked which kolaches could sit there unrefrigerated. A lab measured each filling on three batches:
| Kolache | pH | Water activity | Table | Result |
|---|---|---|---|---|
| Apricot | 3.8 | 0.84 | B | Non-TCS |
| Poppy seed | 6.2 | 0.86 | B | Non-TCS |
| Cream cheese, open case | 4.9 | 0.94 | B | Product assessment required |
| Cream cheese, wrapped warm | 4.9 | 0.94 | A | Non-TCS |
| Sausage klobasnek | 6.0 | 0.96 | B | TCS: it's meat |
The sausage klobasniky went into a hot case at 135°F. For the cream cheese, four hours of time control ran out before lunch, and wrapping each one warm would have taken them out of the open case. So the shop sent the recipe and three batches to a university food science lab for a challenge study of eight hours at room temperature. The study supported eight hours, and the health department granted a variance on the condition that each tray is marked with its baking time and pulled at eight hours. The kolaches' recipe can't change without a new look. How long baked goods keep past the day is in shelf life testing.
Get the workbook
Download the TCS check and lab list. Two sheets. TCS check: each food's heat treatment, packaging, pH and water activity; the table and whether it's non-TCS or needs a product assessment fill in. For the lab: what to give a lab for a challenge study, with a status for each. It's an ordinary Excel file with no macros, and it works in Google Sheets, LibreOffice and Numbers.
Where this stops working
The variance is for the recipe the lab tested. A filling made with a different cream cheese, or with less sugar, can have a different water activity, and nothing on the tray shows it. Only the batch record does.
How TaroStack does it
TaroStack keeps each recipe by weight, so the study's recipe stays the recipe.
Recipes by weight. The cream cheese filling is its own recipe, with its cream cheese, sugar and egg by weight.
Receiving by supplier and lot. Each delivery of cream cheese is received from its supplier with its lot, so a switch of supplier is on record.
Batches by lot. Each morning's filling is a batch recording which lots it used.
| The job | Notebook | In TaroStack |
|---|---|---|
| Which recipe the filling followed | Remembered | Each batch from its recipe |
| A new cream cheese supplier | Noticed later | Each delivery by supplier |
| Which lots went into a morning's filling | Not recorded | Batches by lot |
Recipes, batches and lots are on every plan, from $49 a month. The first 30 days are free, with no credit card. If you'd like a hand setting up, ask, and we'll do it with you.