THE SANITARIAN’S FILE
By Robert W. Powitz, Ph.D., MPH
Sampling, Part I:
The Basics
Sampling is part of inspection; sampling and inspection cannot be separated. In the context in which we use it, sampling
is a process or technique used in food
safety to select a representative part of
a food or foods, or things and conditions having to do with food for the purpose of determining parameters or characteristics of the whole. That is a long-winded way of
saying that we select a small part of the whole as a sample for inspection or analysis. This may include time and temperature measurements; measurements of cleanliness; evaluations of handwashing;
and taking light, water activity and chemical concentration readings—
just to touch upon a few of the things at which we routinely look.
Sampling is not a difficult concept until we realize that in producing a set of
samples that are representative of the source under investigation (and possibly suitable for subsequent analysis), the axiom “garbage in equals garbage out” takes on a
whole new dimension.
Sampling Objectives
To give some clarity to this concept, sampling has several interrelated objectives
when it comes to the sanitarian’s role in the field. First, there are numerous regulations that border on shades of gray. Their endpoints are blurry at best, and in many
instances, one regulation is dependent upon another for an intended outcome. The
act of sampling helps us to define an endpoint. More often than not, it provides a
defined target for the operator in an otherwise nebulous world.
Second, sampling validates objective
measurements. These measurements are
clearly articulated in the regulations
through some finite numbers, generally
given as minimum values. Sampling lets
us know how and to what extent our target meets these values. There is probably
more abuse associated with this objective than any other. These minimum
values do not have ranges associated
with them, and yet we tend to measure
them with instruments that do. Additionally, we know that the more finite a
value, the more variables can be identified that affect that value.
Third, a good sampling strategy refines subjective observations. People
often see the same thing differently and
each of us ascribes our own interpretation to subjective parameters. For instance, the phrases “clean to sight and
touch,” “adequate” and “as necessary”
are quite open-ended. Whenever possible, sampling can give some objectivity
to these seemingly meaningless requirements.
While these objectives are all well
and good, samples that are not representative of the source are of little use. Likewise, poor collection or detection
procedures yield unrepresentative samples and contribute to the uncertainty of
the analytical results. All too often, I see
this among my peers, but also with
third-party providers such as independent auditors, as well as with in-house
quality control personnel. We are all
guilty to some extent and yet we wonder
“why?” when something goes wrong.
To put this in some perspective, I was
recently retained as an expert witness for
the defendant in an alleged foodborne
outbreak. What gave me pause and
prompted this article was a simple entry
on an official inspection form that
stated, “Gravy was at 81 °F.” This was
listed as a critical violation. In explaining the entry, the inspector wrote,
“Gravy should be kept at 140 °F.” Wow.
Taken at face value, the explanation
doesn’t seem that far afield, except when
a lawsuit hangs in the balance. There
was no time given for the sample; the
