Tag Archives: kashering

Torah, Science & Kashrus in the Classroom

By: Rabbi Dovid Heber

Spring 2025

Over the years, I have been invited on multiple occasions to speak at various girls’ high schools in Lakewood about the impact of astronomy on the Jewish calendar and halachic zmanim. The inherent message I have aimed to give over is that one needs a basic understanding of math and science to fully comprehend certain halachic issues.

For example, the earth’s rotation on its axis is the basis of zmanei hayom (halachic times of the day) that are so much a part of our lives with regard to davening times and knowing when Shabbos and Yom Tov begin and end. One needs to know how the moon rotates around the earth to better understand Rosh Chodesh and the Jewish calendar. Indeed, Chazal had keen insights into scientific topics that were discovered hundreds of years later by researchers.

Investigating how a product is manufactured and analyzing the composition of the raw materials […]

Oven Kashrus 101: Using the Same Oven for Meat, Dairy, Fish and Pareve

By: Rabbi Dovid Heber

Spring 2016

If your kitchen is equipped with four ovens – for meat, dairy, pareve and fish – you don’t need to read this article. However, if you do not have such a luxury, you will find various halachic details enumerated below quite relevant.

There are numerous factors involved in an oven “going back and forth” between meat and dairy or using an oven for fish or pareve.1 They include the following:

The oven: Is it clean? Was it kashered? When was it last used?

The food: Is it liquid? Is it covered? When was it prepared?

Does the question arise to do the action l’chatchila (I can do this) or is it only okay bedi’eved (it already happened)?

NOTE: The halachos addressed are based on the psak of HaRav Moshe Heinemann shlit”a, STAR-K Rabbinic Administrator.2 This article addresses issues only involving regular gas or electric ovens. It does note address […]

Which Materials May Be Kashered (and Which May Not)

By: Rabbi Mordechai Frankel

Kashrus Kurrents Summer 2012

Q: I have a number of utensils which need kashering through hagalah (immersion in boiling water). Which materials may and may not be kashered?

A: A fleishig utensil which comes into contact with hot milchig food or a milchig utensil which comes into contact with hot fleishig food needs to be kashered before further use. There are a number of methods for kashering, dependent upon the manner of contact between the utensil and the food. Perhaps the most common form of kashering is hagalah, in which the utensil is immersed in boiling water.

Metal
The Torah tells us that a vessel may be kashered if it is made from one of six metals: gold, silver, copper, iron, tin or lead.1 There are other metals and alloys which were not in common use at the time of Matan […]