Beyond the Bottle: Understanding Essential Oils
2nd Edition

Do you ever wonder if judging an essential oil’s quality or purity must involve some kind of superpower? Biologist Dr. Petra Ratajc is going to uncloak this mystery and pass this specialized ability on to you. 

Also offered as a part of Diploma in Aromatic Science


This five-part online certification course is a deep dive into how essential oils are made from the soil up.

UPDATED in 2023, this is the complete journey from cultivation to cracking the lid on the bottle in your hand, with highlights on production, sustainability and quality control.

Where do essential oils come from and why do plants create them? Should you grow your own lavender for home distillation? How do you really know what you’re getting when buying essential oils? How do you know if an essential oil has been adulterated, or has oxidized? And how can you make sensible, sustainable choices?

In this groundbreaking course, you’ll no longer be at the mercy of marketing that may not be accurate, or doesn’t address what you really need to know. Instead, you’ll learn about analyzing essential oils by decoding their growing conditions and plant biology, as well as their composition.

What You Get in the Course

Join Petra on five 60-minute live lessons over 5 weeks.

Extra time to ask anything you may want to know about essential oils, immediately following each live lesson.

Every session is recorded if you are unable to attend live.

Downloadable handouts and course notes with links to additional resources.

Online forum for your questions and interaction with Petra, the TI team and classmates.

A signed Certificate of Completion from the Tisserand Institute.

Ongoing access extended access for 8 weeks after the last lesson, and 6 months of view-only review access.

Plus, Get These Extra Bonuses

A valuable infographic that leads you through the decision process for making smart, environmentally friendly essential oil purchases.

A handy chart of botanical and common names for easy reference, with an extra column to add names in your language.

Petra Ratajc, PhD

Biologist | Researcher | Educator

On her myth-busting plant biology blog, The PhytoVolatilome, Petra refers to herself as an aromatic plants enthusiast. But click through to just one of her posts, and it’s obvious that she’s so much more than that – and backed by some serious credentials.

Petra Ratajc has a post-graduate degree in Biological and Biotechnical Sciences from the University of Ljubljana. Her PhD extends from fieldwork to molecular research in the quality, safety and efficacy of aromatic herbs and their essential oils. Petra specializes in medicinal and aromatic plants, secondary plant metabolites, pharmacognosy and pharmacology – specifically focused on plant volatile constituents.

Besides bringing an unequivocal depth of knowledge to this course, Petra is an experienced lecturer and presenter at various seminars and workshops.

Course Breakdown

Here is what you will learn with us this year.


Lesson 1 - The Plant
  • What is an essential oil? Defining it in scientific terms
  • Plant volatiles and their roles in plants and the environment
  • Where and how plants produce EO constituents/plant volatiles
  • Demystifying botanical names and why we shouldn’t be afraid of them
Lesson 2 - The Grower
  • How cultivation and environmental factors influence essential oil composition
  • Chemotypes: the interplay between genetics and the environment
  • The pros and cons of wildcrafting and cultivation
  • Conventional vs. organic cultivation: standards, certifications and sustainability
  • How climate change affects aromatic plants and essential oil production
Lesson 3 - The Extraction
  • Different methods of extraction lead to different resulting  extracts, even from the same plant material
  • Distillation and mechanical expression
  • Steam-distilled oils, expressed oils and hydrolats
  • Solvent extraction, absolutes, concretes and flower waxes
  • CO2 extraction and different types of CO2 extracts
  • A global look at essential oil production
Lesson 4 - The Product
  • Why a ‘pure’ oil is not necessarily a ‘quality’ oil
  • Understanding physical properties: specific gravity, optical rotation, refractive index
  • How to read a gas chromatography-mass spectrometry report
  • Olfactory evaluation
  • Adulteration, contamination and their consequences
  • The pros and cons of essential oil standardization
NEW Lesson 5 - The Customer
  • What is Certificate of Analysis (CoA) and why is it important
  • How to find good quality information about essential oils
  • How to evaluate an essential oil in terms of quality, composition, sustainability and price
  • How essential oils are traded and who are the users of essential oils

When You Complete the Course

Essential Oil Creation, Purpose and Sustainability Certification
Upon completion, your certificate – issued by the leaders of evidence-based instruction – shows your deep knowledge of essential oil production and sustainable practices.

What previous students say about our courses:

The material provided data that is important to me. It was presented in a way that I found mentally digestible. Instructors are pleasant; all interaction was very good. ~ Nada Fifonja

Fantastic course. I can always be sure that the quality and content of courses from Tisserand Institute will be exceptional! ~ Barbara Carlson

Getting most recent information on all the important aspects of essential oils. It was really BEYOND the bottle. Thank you, I really enjoyed it!

The wealth of information that was provided was excellent.

Very interesting and thorough. Thank you to Dr Petra for sharing her knowledge. ~ Jo Pownall

Discover how to evaluate essential oils from the soil up to ensure that you know what’s in the bottle, and that you get the quality you need.


Will there be notes for me to review?
Yes. Each lesson comes with printable handouts of the slides used in the lesson, and additional lesson notes. These are sent to you before each lesson and are for you to keep and refer to at any time.
I am a certified aromatherapist. Will I learn anything new?
Many of our students have commented that our courses helped them grasp what they learned elsewhere in more detail, or complemented their previous education. Some of our students are lifelong learners, and some are teachers.
I am new to essential oils. Is this course for me?
We will let one of our previous students answer this one:

“The information presented is appropriate for all levels, and although I am just beginning my aromatherapy journey it all makes sense.”

Will there be assessments or exams? What kind?

Each weekly lesson is followed by a multiple choice quiz, and there is a summary test at the end of each course. Passing both the weekly quizzes and the final tests is a requirement for certification.

You will be given enough time to prepare for the test as well as three attempts to pass. 

Will I be able to ask questions?

Absolutely! In addition to the live Q&A sessions, you can post your questions in the dedicated student forums where the tutor and the TI team will address them. 

What if I cannot participate on a live session?

All of our live sessions are recorded and are posted on the learning platform within 24 hours so you can watch them, or rewatch as needed during the course. 

How long will I have access to the recordings?

You will have access to all the videos for at least four weeks after the last lesson (see course description for clarification as this changes for individual courses). All the printable materials (notes, handouts, charts, etc.) are of course yours to keep for reference forever.

Do you offer continuing education credits?

Because we have students from all over the world and of many professions we are not able to offer credits for specific organizations – there are simply too many. However, we issue a confirmation of CE hours gained on the course that you can apply with your professional organization and will be happy to assist with any additional documentation.

At the moment, we are an Approved Continuing Education Provider with NAHA. 

What if I fall behind or cannot attend classes?
We have found that running classes on specific dates works best to help you finish a program. You join a class of students, and learn along with them. Many students help each other with queries, and of course our tutors are there too. That said, if you miss a few classes you should be still able to comfortably jump right back in and if you do fall behind you can request extra time. Of course this cannot be indefinite, but we do our best to help you get your certificate.