First of all, I apologize to all members of this forum, red.november included, for my emotional outburst. I also apologize to the member whose quote I lifted from another thread. This is the first forum that I have ever signed up for and didn't realize that removing his name from the quote did not guarantee his anonymity because I didn't know that the quote line was actually a link.
But, also after some thought, I must speak up. Silence is acquiescence.... Please also know that I hold a Bachelor of Science Degree in Horticulture from Oregon State University (1979) and my major course of study was Herbaceous Plants. I also worked for a famous plant geneticist at the OSU research farm full time for 5 summers and PT in the greenhouse ranges during the school year. He was also my major professor. I have studied and worked in the food industry for 32 years. I think those are reasonable credentials.
Oregano, tarragon, mint and other perennial herbs are quite often harvested twice a year. If an herb can bloom more than once a year, it will be harvested more than once a year. Herb cultivators aren't going to just let money sit out there in the fields.
This is partially correct: perennial herbs are often harvested twice a year... but what is misleading about this statement is that normally, all harvests of culinary herbs for the dried herb market occur during THE SAME GROWING SEASON, most usually in mid-summer and early fall before the first frost. Perennial herbs go through a dormant period in the winter when essential oil levels fall and leaf production slows to very little or nothing (the plant puts any energy it has into root production to support the spring flush of growth), making off-season commercial harvest unreasonable from both an economic and quality standpoint. There are some growers, mainly in Southern CA, where there is seldom fear of frost and winter doesn't exist... who harvest year-round, but they generally grow for the organic and fresh herb markets, which IS economically feasible based on the prices paid for these products by the consumer.
Therefore, I stand by the statement that herbs are harvested "once a year". They are then dried, processed and bottled... once a year.
Also, the second sentence of the above quote begs the question of the necessity of flowering for harvest. In actuality, herbs are harvested BEFORE flowering because said flowering causes the levels of the essential oils in the leaves to drop which leads to a decrease in the flavor of the plant materials. Flowering can also cause a decrease in the production of leaves (the energy of the plant is focused on flowering, so that it can reproduce itself before the season is over), and both of these issues are detrimental to crop quality, unless, of course, you're growing culinary lavender or the like.
Also, since my last post on this public forum, I have done a lot of research on the internet, visiting the websites of Tones (spiceadvice.com/usage), mccormick.com, spicebarn.com, spicehouse.com and the website of The Herb Companion magazine and they ALL agree with the Penzey's advice that I originally posted, both the once-a-year purge of your seasonings cupboard as well as the "scratch-n-sniff" freshness test. None of these companies qualified their statements in any way... the natural assumption made by the consumer reading these recommendations is that they have been USING said herbs and spices all along, not leaving them sit unopened in a dark cupboard. I did find one company on the internet who will, for a premium price, grind herbs and spices to order, but they are what's called a "special niche" company.
So, the bottom line for all the folks out there trying to make the tastiest pizza sauce they can: replacement of herbs is based on personal preference and palate sensitivity. Crush some between your fingers... if it doesn't smell strongly of the herb you're using, replace it. Tossing your herbs every 6 months might get you SOMEWHAT fresher (i.e. unopened) herbs. However, if you keep your herbs in tightly-closed jars in a cool, dark cupboard, they may be fresher than those on the grocery store shelves which are exposed to light, often 24 hours/day, and often not rotated by busy employees who also donít have time to check pull dates regularly (Iíve worked in grocery stores for many years!) all of which can also degrade the product. The point is, use your own judgement, but be aware that culinary herbs for the dried herb market are not harvested year-round, and if you replace often, what you replace will probably be the same "age" as what you replace it with.